Symposium Organizers
Ying Chen, Rensselaer Polytechnic Institute
Erik Bitzek, University of Erlangen-Nuremberg
Maria Teresa Perez Prado, IMDEA Materials Institute
David Rowenhorst, U.S. Naval Research Laboratory
PM03.01: Interface Structure and Structural Evolution
Session Chairs
Ying Chen
David Rowenhorst
Monday PM, November 27, 2017
Sheraton, 3rd Floor, Commonwealth
8:15 AM - *PM03.01.01
Exploring Models, Mechanisms and Representations for Grain Boundary Properties
Elizabeth Holm 1 , Ian Chesser 1 , Xiaoting Zhong 1 , Gregory Rohrer 1 , Ankita Mangal 1
1 , Carnegie Mellon University, Pittsburgh, Pennsylvania, United States
Show AbstractThe properties of grain boundaries, including energy and mobility, influence the microstructure and performance of polycrystalline materials. As such, boundary properties have been a focus of molecular dynamics (MD) simulations. In addition to directly measuring boundary properties, MD results are often examined for the atomic structures and mechanisms that govern the properties of interest. This approach has generated considerable insight, especially for particular classes of boundaries. However, grain boundaries exist in a vast crystallographic space as well as in diverse environments under varying driving forces. In this work, we explore grain boundary representations based on structure at various length scales in order to parameterize how much structural and physical information is required to create a predictive model. For example, we develop and train a random forest machine learning model to extract the most important crystallographic descriptors for predicting grain boundary energy and mobility; this approach enables us to separate the influence of macroscopic (crystallographic) and microscopic (structural) degrees of freedom. Similarly, for faceted boundaries with the same microscopic structure, we explore the extent to which physical factors, such as bonding and driving force, can affect boundary motion. Finally, for boundaries in motion, we examine how they sample the space of atomic structures and relate that to the mobility. In all cases, the goal is to leverage MD simulations for broader understanding of grain boundary properties.
8:45 AM - PM03.01.02
An Efficient Monte-Carlo Algorithm for Determining the Minimum Energy Structures of Interfaces
Arash Dehghan Banadaki 1 , Mark Tschopp 2 , Srikanth Patala 1
1 , North Carolina State University, Raleigh, North Carolina, United States, 2 , U.S. Army Research Laboratory, Adelphi, Maryland, United States
Show AbstractSampling minimum energy grain boundary (GB) structures in the five-dimensional crystallographic phase space can provide much-needed insight into how GB crystallography affects various interfacial properties. However, the complexity and number of parameters involved often limit the extent of this exploration to a small set of GBs. In this article, we present a fast Monte Carlo scheme, which includes the removal and insertion of GB atoms, for generating zero-Kelvin, minimum energy GB structures. We have validated the robustness of this approach by simulating over 1184 tilt, twist, and mixed character GBs in both fcc and bcc metallic systems.
9:00 AM - *PM03.01.03
Fast Fourier Transform Micromechanical Modeling of Interfacial Defects Mechanical Fields and Applications
Stephane Berbenni 1
1 , LEM3, UMR CNRS 7239, Université de Lorraine, Metz France
Show AbstractInterfaces play a critical role on the mechanical properties of many engineering materials. Continuum mechanics based modeling of interfacial defects is a fundamental issue to predict the mechanical behavior of nanocrystalline materials and to understand the mechanical interactions between bulk and interfacial defects. Here, a numerical spectral approach based on the efficient Fast Fourier Transform (FFT) algorithm is developed to solve both dislocation and disclination mechanical fields in heterogeneous media like bi-crystals, laminates, polycrystals, inclusion-based composite materials. Given a spatial distribution of dislocation and disclination densities in such materials, which can be obtained from experimental data, the incompatible and compatible elastic strains, elastic curvatures as well as the stress fields are obtained without singularities at defect cores from the solutions of Poisson and Lippmann-Schwinger equations in the Fourier space. The defect mechanical fields in the vicinity of the defects are accurately solved by the proposed Discrete Fourier Transform method, devoid of spurious numerical oscillations inherent to classic spectral approaches. The numerical applications include the mechanical fields of different interfacial defects: (i) grain boundaries seen as DSUM (i.e. Disclination Structural Unit Model), (ii) twin tips present in internally twinned lamellae (i.e. intersections between primary and internal secondary twins), (iii) disconnections in grain boundaries, and, (iv) solute segregation at grain boundaries.
9:30 AM - PM03.01.04
Polymorphism of Asymmetric Σ9{111}/{115} Interfaces in Silicon
Yutaka Ohno 1 , Kentaro Kutsukake 1 , Hideto Yoshida 2 , Seiji Takeda 2 , Tatsuya Yokoi 3 , Katsuyuki Matsunaga 3
1 , Tohoku University, Sendai Japan, 2 , Osaka University, Osaka Japan, 3 , Nagoya University, Nagoya Japan
Show AbstractGrain boundaries are inevitably introduced in polycrystalline silicon (Si) ingots for solar cells, and they have substantial influences on electronic properties such as minority carrier lifetime, via the segregation of impurity atoms. Especially, asymmetric GBs with higher-Σ value of the associated coincident site lattice (CSL) are frequently introduced in Si ingots even though their GB energy is fairly high, and they severely affect the overall material properties even when their density is low. A comprehensive knowledge of the structural properties of the GBs is, therefore, indispensable to produce cost-effective high-efficiency solar cells by controlling the introduction of those detrimental GBs.
In the present study, we discuss the structural stability of asymmetric Σ9{111}/{115} GBs with the <110> tilt axis. In a cast-Si ingot, a GB has a periodic interface structure with a period of 2 nm along the GB, composed of 10 Si dumbbells which cannot be assigned to one of the two grains and 4 single-atomic columns with the stretched <110> reconstructed bonds [1]. The distorted dumbbells are oriented such that they form nano-Σ3{111} sub-boundaries, suggesting a low GB energy in the range of the highly symmetric low-Σ GBs [1]. Meanwhile, we have found a different interface structure with the similar period length in Czochralski (CZ)-grown Si ingots: one GB unit is composed of 4 distorted dumbbells forming nano-Σ3{111} sub-boundaries and 2 single-atomic columns, revealed by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) [2]. Unlike in the former GB unit, the HAADF signal of the atomic columns do not drop in the latter GB unit, indicating that the latter GB unit would not involve partial site occupancies and static atomic displacements. Considering the small number of the stretched <110> reconstructed bonds and small atomic strains, the latter GB unit would be more stable than the former one. The formation process and stability of the polymorphs will be discussed by using simulated annealing in the tight-binding approximation.
[1] A. Stoffers, et al., Phys. Rev. Lett. 115 (2015) 235502.
[2] Y. Ohno, et al., Appl. Phys. Lett. 110 (2017) 062105.
10:15 AM - *PM03.01.05
Energy States During Thermally Driven Grain Growth
Mukul Kumar 1 , Jonathan Lind 1 , Shiu Fai Li 1
1 , Lawrence Livermore National Lab, Livermore, California, United States
Show AbstractPolycrystalline microstructures in metals and ceramics are composed of grain boundaries, where most of the excess free energy of the system resides. Because of the metastable nature of polycrystalline microstructures, the grain boundary population dictates the thermodynamics and the kinetics of the system. Recent experimental studies show significant levels of reduction in thermally-driven coarsening rates in microstructures with a high frequency of low energy (or so-called special boundaries). Grain growth is considered to be driven by the reduction of curvature of the individual interfaces. Consequently, a grain boundary with a higher degree of disorder, or higher energy, would have greater impetus to reduce its surface area (by straightening or reducing curvature) thereby reducing its contribution to the overall energy content. An understanding of the relationship between the grain boundary energy and population distributions is a critical step in our understanding of this phenomenon. Characterization of the grain boundary energy distribution (GBED) is challenging, as it involves combining the difficult problems of measuring energies of individual boundaries with statistically significant sampling of the population. Advances in the experimental realm combined with development of a universal model for grain boundary energies in FCC symmetry crystals enables us now to robustly map the GBED in polycrystalline microstructures. The result is a description of the boundary energy as a function of all 5 macroscopic degrees of freedom. Armed with these two tools we have quantified the evolution of GBED in microstructures during thermal grain growth. As a comparison two microstructures with significantly different starting boundary populations in high purity copper are considered. Microstructural evolution in these two states will be discussed in the context of our traditional understanding of steady state grain growth.
This work was performed under the auspices of the US Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344, and the authors were supported by US DOE Office of Basic Energy Sciences, Division of Materials Science and Engineering.
10:45 AM - *PM03.01.06
Measuring Changes in Grain Shapes and Sizes in Polycrystalline Ni During Grain Growth
Aditi Bhattacharya 1 , Chris Hefferan 1 , Shiu Fai Li 1 , Jonathan Lind 1 , Robert Suter 1 , Gregory Rohrer 1
1 , Carnegie Mellon University, Pittsburgh, Pennsylvania, United States
Show AbstractThe three-dimensional structure of polycrystalline Ni was measured at five points in time separated by 30 min anneals at 800 °C. The locations, orientations, and shapes of roughly 2000 grains were determined at each time step by near field high-energy diffraction microscopy. The data make it possible to determine the grain boundary character distribution, the relative grain boundary energies, and the grain boundary curvature distribution at each time during the interrupted thermal annealing. Although there are some changes in the grain boundary character distribution with time (for example, the concentration of grain boundaries with a 60°/[111] disorientation increases) the changes in these statistically averaged quantities are not dramatic. On the other hand, the shapes and sizes of individual grains do change significantly. Using size, orientation, and location as selection criteria, individual grains were identified and tracked throughout multiple anneal states. These data make it possible to compare the changes in volume with time to a grain’s volume, numbers of faces, integral mean curvature, and the characteristics of its neighbors. We have tracked nearly 500 grains throughout the five anneal states. These are a subset of grains that do not touch the surface of the observed volume in any anneal state and survive for the entire experiment. We find that while accepted growth laws are obeyed (larger grains with more sides grow and smaller grains with fewer sides) on average, the details are far different. For example, approximately 30 % of the grains have a sign of volume change that is different from that predicted based on the size or number of nearest neighbors. The local curvature and the grain neighborhood are thought to be deciding factors in determining whether an individual grain shrinks or grows.
11:15 AM - PM03.01.07
The Anisotropy of Grain Boundary Curvature in Metallic Alloys
David Rowenhorst 1
1 , U.S. Naval Research Laboratory, Washington, District of Columbia, United States
Show AbstractIt has long been understood that grain boundary interfaces demonstrate anisotropies based on the five parameter crystallographic character of the interface, but measurements of grain boundary geometries have been difficult due to the large crystallographic parameter space and the complex 3D geometries that need to be measured. Advances in three-dimensional characterization, especially serial sectioning in combination with Electron Backscattered Diffraction (EBSD), have made it possible to collect datasets that contain tens of thousands of boundaries at high resolutions, making these measurements now possible. In this talk we will present how these 3D techniques can be used to show the populations and curvature of grain boundaries in metallic systems are influenced not only by the interfacial energies, but also the topology of the energy function, and that these affects influence the microstructural evolution of these systems.
11:30 AM - PM03.01.08
A Mesoscale Model of Grain Boundary Faceting—The Role of Facet Junction Energetics
Fadi Abdeljawad 1 , Douglas Medlin 2 , Jonathan Zimmerman 2 , Khalid Hattar 1 , Stephen Foiles 1
1 , Sandia National Laboratories, Albuquerque, New Mexico, United States, 2 , Sandia National Laboratories, Livermore, California, United States
Show AbstractInterfaces, free or internal, greatly influence the physical properties and stability of materials microstructures. Of particular interest are the processes that occur due to anisotropic interfacial properties. In the case of grain boundaries (GBs) in metals, an initially flat GB may facet resulting in a “hill-and-valley” morphology with well-defined planes and corners/edges connecting them. In general, dislocation-like defects exist at GB facet junctions due to differences in the translation states at these intersecting facets. Based on a diffuse interface model capable of accounting for strongly anisotropic GB properties, we examine GB faceting and subsequent facet coarsening dynamics. The hallmark of our approach is the ability to independently examine the various factors affecting this interfacial instability. More specifically, our formulation incorporates higher order expansions to account for the excess energy due to facet junctions and their non-local interactions. As a demonstration of the modeling capability, we consider the case of a ∑5 <001> tilt GB in BCC Iron, where faceting along {210} and {310} planes has been experimentally observed. Atomistic calculations are used to construct the GB energy-inclination phase diagram, which is then used as an input in our model. Linear stability analysis and simulation results highlight the role of junction energy and associated non-local interactions on the faceting instability and subsequent facet coarsening. Finally, we discuss extending the model to three dimensions by considering the interfacial stiffness tensor in polar coordinates, where the ∑3 GB in Nickel is used as an example.
This work is supported by the Laboratory Directed Research and Development program at Sandia National Laboratories, a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.
11:45 AM - PM03.01.09
Multiscale Thermodynamic and Kinetic Modeling of Interfaces for Solid-State Hydrogen Storage Materials
Tae Wook Heo 1 , Shinyoung Kang 1 , Xiaowang Zhou 2 , Keith Ray 1 , Tadashi Ogitsu 1 , Mark Allendorf 2 , Brandon Wood 1
1 , Lawrence Livermore National Laboratory, Livermore, California, United States, 2 , Sandia National Laboratories, Livermore, California, United States
Show AbstractHydrogen is an excellent, efficient, and clean energy carrier. Solid-state inorganic materials such as complex metal hydrides are promising solutions for lightweight, compact, and low-pressure onboard hydrogen storage. Many of the biggest challenges in the hydrogen storage research arise from the fact that the operating mechanisms often involve the complicated coupling of various interfacial processes. The associated chemical and materials processes including gas-surface reaction, surface/bulk/interface mass transport, structural modification, and intermediate phase nucleation-and-growth occur over wide ranges of length and time scales, which in turn play key roles in determining the overall performance of hydrogen storage processes. Essentially, these are collective and concurrent dynamic processes of atomic/molecular species that determine the thermodynamics and kinetics of nano- or micro-level characteristics. However, the lack of foundational understanding of relevant interfacial mechanisms and their impacts on hydrogen storage reactions has hampered the acceleration of storage materials development and deployment. In this talk, we present our collaborative effort as part of the DOE Hydrogen Storage Materials—Advanced Research Consortium (HyMARC) under the Energy Materials Network (EMN) towards the multiscale modeling of solid-state hydrogen storage. In particular, we will discuss our recent efforts on establishing the integrated interfacial modeling framework for investigating several types of interfaces and coupled processes. Examples will include modeling studies of (i) the kinetic interface and phase evolution in simple interstitial hydrides (e.g., Pd-H); (ii) roles of interface-induced chemical and mechanical strain energies and their impacts on the thermodynamics and kinetic reaction pathways in simple and complex hydrides (e.g., Mg-H, Li-N-H); and (iii) beyond-ideal kinetic and morphological behaviors of reactive and/or defective interfaces of complex hydrides (e.g., Mg-B-H) during (de/re)hydrogenation processes.
This work of was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 (T.W. Heo, S. Kang, K.G. Ray, T. Ogitsu, and B.C. Wood) and by Sandia National Laboratories under contract DE-AC04-94AL85000 (X.W. Zhou and M.D. Allendorf).
Symposium Organizers
Ying Chen, Rensselaer Polytechnic Institute
Erik Bitzek, University of Erlangen-Nuremberg
Maria Teresa Perez Prado, IMDEA Materials Institute
David Rowenhorst, U.S. Naval Research Laboratory
PM03.04: Deformation Mechanisms at Grain Boundaries
Session Chairs
Erik Bitzek
Rebecca Janisch
Tuesday AM, November 28, 2017
Sheraton, 3rd Floor, Commonwealth
8:15 AM - *PM03.04.01
Plastic Deformation by Grain Boundary Motion—Experiments on Bicrystals and Evaluation of Boundary Migration-Shear Coupling
Konstantin Molodov 1 , Dmitri Molodov 1
1 , RWTH Aachen University, Aachen Germany
Show AbstractThe results of experimental measurements of grain boundary migration coupled to shear deformation will be reviewed. For many symmetric tilt grain boundaries, which were studied experimentally as well as examined in computer simulations, the boundary motion coupled to shear can be evaluated using the geometric model of coupling by Cahn et al. [Acta Mater 54 (2006) 4953]. However, there are a number of interesting and important exceptions. In particular, the relations derived based on this model cannot directly predict the correct amount of shear produced by <110> tilt boundaries with misorientations in the range between 35° and 55°, for example Σ11 {113} and Σ9 {221} symmetric tilt boundaries, for which the amount of shear is known from experiments on Al and zirconia bicrystals and atomistic simulations for Al, Cu and Ni. Furthermore, these relations fail to reveal the coupling behavior associated with a number of deformation twins in various crystalline structures including well-known and comprehensively studied Σ3 (111) and (112) twins in cubic, (10-12), (10-11) and other twins in hexagonal and other crystalline systems.
In the current work the solutions of the Frank-Bilby equation for the dislocation content of symmetric tilt grain boundaries were analyzed for a number of grain and twin boundaries. Based on this analysis, the geometrical model of grain boundary migration - shear coupling was extended to evaluate the coupling factor (amount of shear) for twin and grain boundaries in various crystal structures. The coupling factors calculated according to the proposed general formula are in excellent agreement with respective experimental and simulation data known from literature. For a given grain/twin boundary the coupling factor was found to result from a combination of two elementary coupling modes, the balance between which is constituted by an introduced weight factor. Hence, the coupling factor (or the twinning shear) depends not only on the tilt angle of the grain/twin boundary, but also on the weight factor, which may vary for crystallographically equivalent boundaries. With respect to deformation twinning, the weight factor is intimately linked to the amount and direction of twinning shear produced by the boundary. A variation of the weight factor for the same boundary can be interpreted as a result of a structural change of the grain/twin boundary, i.e. grain boundary phase transformation.
8:45 AM - PM03.04.02
Coupling between Grain Boundary Sliding and Migration—Misorientation Dependence
Askar Sheikh-Ali 1
1 , Institute of Rheotechnologies LLC, Almaty Kazakhstan
Show AbstractGrain boundary sliding behavior has been studied in zinc bicrystals with symmetric tilt boundaries slightly deviated from 123.75°<10-10>Σ=9 coincidence misorientation. The boundaries span a narrow range of misorientation of 123.6° ≤θ≤131.7°. All investigated boundaries except 131.7°<10-10> boundary demonstrate coupling between grain boundary sliding and migration predicted by DSC-dislocation model. The ratio between boundary sliding and migration is almost the same for all boundaries experiencing coupling between these processes. Sliding along 131.7°<10-10> boundary is not accompanied by regular boundary migration. The transition from coupling to migration free sliding occurred at deviation angle determined by Brandon criterion and was interpreted as a transition from special to general boundaries. Within the accuracy of the experiment, the transition angle remains constant up to the maximum investigated temperature of 673K (0.97Tm, where Tm is the melting point).
9:00 AM - *PM03.04.03
Deformation Mechanisms at Grain Boundaries in Al and TiAl—Atomistic Mechanisms and Their Effective Description
Rebecca Janisch 1 , Mansour Kanani 2 , Alexander Hartmaier 1
1 , Ruhr-University Bochum, Bochum Germany, 2 , Shiraz University, Shiraz Iran (the Islamic Republic of)
Show AbstractSystematic relationships between a limited number of fundamental material properties and the observable behaviour of a material are needed for successful design of new materials. On the continuum level advanced hierarchical models exist, which describe the microstructure-property relationships even in complex multiphase microstructures very well. However, usually such models still have to make assumptions about the relative importance of different deformation mechanisms on the atomic scale. In our work we investigate such mechanisms by means of molecular dynamics simulations and ab initio density functional theory calculations, with a focus on grain boundaries in metallic microstructures.
Interfaces in metallic micro- and nanostructures play a role during plastic deformation in many respects. Besides accomodating part of the plastic strain by means of grain boundary sliding and migration they can act as sources, sinks, or barriers for dislocations, as well as as crack nucleation sites. Especially in interface dominated microstructures such as lamellar TiAl, they thus can rule the overall mechanical behaviour. High resolution experimental methods can visulize the underlying atomistic processes. However, since these processes are not independent, usually several of them occur at the same time. To isolate the intrinsic deformation mechanisms of grain boundaries we have carried out molecular statics and molecular dynamics simlations of bicrystal shear at different interfaces in Al and TiAl. Four distinct mechanisms could be identified, namely rigid grain sliding, grain boundary migration, coupled sliding and migration, and dislocation nucleation and emission. Depending on the loading direction different mechanisms can occur at one and the same grain boundary, i.e. there is a pronounced anisotropy in the interfacial shear behaviour.
Nevertheless, a link can be established between the deformation mechanisms and fundamental properties that can be obtained by quantum mechanics based electronic structure methods and at interfaces can be established. We introduce the shear instability energy, which can be determined from a generalized stacking fault energy surface calculation, and it is characteristic for the dynamic deformation mechanisms obtained via molecular dynamics simulations of bicrystal shear. Furthermore the shear instability energy can be used to scale between the results of calculations with different interatomic potentials, i.e. also to evaluate trends in deformation mechanisms across different elements. In this the concept of the shear instability energy is more comprehensive than models which rely only on the ratio of unstable and stable stacking fault energy. This makes it a promising tool for enhancing high-throughput characterization of materials.
10:30 AM - *PM03.04.05
Assessment of Damage Behavior of Aluminum Using Diffraction-Amalgamated Grain-Boundary Tracking Technique
Hiroyuki Toda 1 , Kyosuke Hirayama 1 , Masakazu Kobayashi 2 , Akihisa Takeuchi 3 , Kentaro Uesugi 3
1 , Kyushu University, Fukuoka Japan, 2 , Toyohashi University of Technology, Toyohashi Japan, 3 , Japan Synchrotron Radiation Institute, Mikazuki cho Japan
Show AbstractA novel experimental method has been developed by amalgamating a pencil beam X-Ray diffraction (XRD) technique with the recently developed grain boundary tracking (GBT) technique. XRD and GBT are both non-destructive in-situ analysis techniques for characterizing bulk materials, which can be carried close to the point of fracture. DAGT provides information about individual grain orientations and 1-micron-level grain morphologies in 3-dimensions together with high-density local strain mapping. An Al-3 mass % Cu model alloy was used to investigate its deformation behavior under tension. The morphology of the grains was determined by the X-ray microtomography imaging and the liquid metal wetting technique, after which GBT provided an accurate description of the position and morphology of all the grains in a region of interests. Diffraction spots in the XRD experiments were related to grains, making it possible to describe crystallographic orientation of all the grains. It has been revealed that deformation is localized at both microscopic and meso-scopic levels. Inhomogeneous deformation was observed in each individual grain. In addition, a group of a few grains coordinately interacts and specific grain boundaries thereby exhibit intense strain localization. Hydrostatic tension was also observed at quadruple junction points and its mechanism was analyzed.
11:00 AM - PM03.04.06
Contribution of Different Types of Interfaces to Strain-Hardening Behavior of Ti-6Al-4V Alloy with Bimodal Microstructure
Yan Chong 1 , Masatoshi Mitsuhara 2 , Tilak Bhattacharjee 1 , Shigeto Yamasaki 2 , Akinobu Shibata 1 , Hideharu Nakashima 2 , Nobuhiro Tsuji 1
1 , Kyoto University, Kyoto Japan, 2 , Kyushu University, Fukuoka Japan
Show AbstractTi-6Al-4V alloy comprised of α phase with HCP structure and β phase with BCC structure has been used in wide applications in aerospace industries due to its high specific strength and good corrosion/oxidation resistance. So-called bimodal microstructure of Ti-6Al-4V alloy is composed of equiaxed primary α grains and the transformed β areas which are mixtures of fine secondary α-lamellae and retained β-lamellae between the a-lamellae. The co-existence of different types of interfaces, including grain boundaries between equiaxed α grains, interfaces between equiaxed α grains and transformed β areas as well as inter-phase boundaries between secondary α-lamellae and β-lamellae complicates the relationship between microstructural parameters and mechanical properties, while at the same time such interfaces provide a variety of combinations of desired mechanical properties in the bimodal microstructure. In this study, deformation responses of the different types of interfaces in a Ti-6Al-4V alloy with a bimodal microstructure were investigated in detail by means of strain field analysis using digital image correlation (DIC) method, stress field analysis coupling high resolution EBSD with cross-correlation method, and dislocation analysis by both conventional TEM and 3-dimenional dislocation tomography technique. It was found that the interfaces between equiaxed α grains and transformed β areas played a critical role in determining the strain-hardening behavior of the bimodal microstructure during tensile deformation. Due to different nano-hardness of equiaxed α grains and transformed β areas, strain incompatibility occurred near the interfaces during tensile deformation, which in turn led to stress concentration near the interfaces. The stress concentration was believed to activate a large number of dislocations with components on {11-22} slip plane in the adjacent equiaxed α grains, as confirmed by TEM analysis. The activation of dislocations was believed to be the main reason for the superior strain-hardening ability of the bimodal microstructure in Ti-6Al-4V alloy.
11:15 AM - PM03.04.07
Deformation at Triple Junctions in Columnar-Grained Nickel
Mingjie Li 1 , David Duquette 1 , Ying Chen 1
1 , Rensselaer Polytechnic Inst, Troy, New York, United States
Show AbstractGrain boundaries play an important role in plastic deformation of polycrystalline metals. This study aims to gain better understanding of plastic strain accommodation near triple junctions where three grain boundaries/three grains meet. In the literature, triple junctions are often found to be stress concentration sites or crack nucleation sites, which might be related to how plastic strain is accommodated in triple junction regions. To minimize three-dimensional grain constraints, we perform uniaxial tensile testing of nickel specimens with a columnar grain structure. In-plane strain fields were measured by the digital image correlation technique, and slip trace analysis was carried out by electron microscopy and atomic force microscopy. Triple junction regions generally exhibit a high degree of strain heterogeneity as well as spatial heterogeneity in lattice rotation. Interestingly, in the present columnar grain structure where out-of-plane grain constraint was relieved, triple junctions that were studied generally exhibit lower strain than adjacent area, and in-plane geometrical constraint for deformation at the triple junction was accommodated by a large degree of local out-of-plane lattice rotation. There are also significant changes in dislocation slip activities when approaching a triple junction. Effect of triple junction character will also be discussed.
11:30 AM - *PM03.04.08
An Almost Unifying Theory for Grain Boundary-Based Plasticity
Marc Legros 1 , Frederic Mompiou 1 , Nicolas Combe 1 , Sylvie Lartigue-Korinek 2 , Dmitri Molodov 3 , Armin Rajabzadeh 1
1 , CEMES CNRS, Toulouse France, 2 , Institut de Chimie et des Matériaux Paris-Est, Thiais France, 3 Institute of Physical Metallurgy and Metal Physics , RWTH Aachen University, Aachen Germany
Show AbstractRevealed in metallic nanocrystals, grain boundary (GB)-based plasticity has been studied for many years under various names: stress-assisted grain growth, grain rotation, grain boundary sliding or shear-coupled grain boundary migration. Based on MD simulations, TEM and in-situ TEM approaches, we will show that a key player in these mechanisms is the disconnexion, a defect that combines a step and a Burgers vector character, and that belongs to GBs, and especially real GBs. The motion of these defects can explain most of the above-mentioned mechanisms depending on the amplitude of both its step and dislocation components. But not all of them. Some observations suggest that some local atomic shuffling also plays a role as clear non-conservative behaviours are detected, probably postponing the expected happy ending of a complete GB-based plasticity understanding.
PM03.05: Interface Engineering for Functional Applications
Session Chairs
Erik Bitzek
Michelle Johannes
Tuesday PM, November 28, 2017
Sheraton, 3rd Floor, Commonwealth
1:30 PM - *PM03.05.01
Understanding Electronic and Ionic Conduction through Engineered Interfaces for Li-Ion Batteries
Michelle Johannes 1 , Corey Love 1 , Noam Bernstein 1 , Sharka Prokes 1 , Mark Twigg 1 , Kyle Crompton 2 , Collin Becker 3
1 , Naval Research Laboratory, Washington, District of Columbia, United States, 2 , Rochester Institute of Technology, Rochester, New York, United States, 3 , U.S. Army Research Laboratory, Adelphi, Maryland, United States
Show AbstractThe interface between the liquid electrolyte and the electrode in a Li-ion battery is inherently
unstable and frequently dangerous (recent high profile battery-induced fires in phones and on
planes have been traced to this region). In the presence of voltage, both the electrolyte and
anode suffer decomposition towards an SEI (solid electrolyte interphase). This new interface is
heterogeneous both chemically and morphologically and consequently poorly understood and
essentially uncontrollable. Our work attempts to circumvent this problem by engineering a
stable, intentional interface to inhibit the SEI. Our optimized engineered interfaces provide not
only electrochemical, but also structural stability. However, this stability is often at odds
with performance since the same processes (electronic and ionic conduction) that are necessary
for good battery cycling are responsible for SEI growth.
In this work, combined computational and experimental studies of alumina (Al2O3) coatings on
battery electrodes are presented to understand how fundamental processes, such as ionic and
electronic conduction, correlate to the structure and character of the interface. We use ALD to
tightly control the thickness of our interface deposition, characterize the resulting structures
using SEM and TEM, and construct coin cells to measure electrochemical performance.
Additionally, we employ two in-situ techniques to visualize the interface stability and properties:
a custom optical camera allows temperature dependent visualization of the growth (or lack
of growth) of the SEI in-operando and atomic force microscopy (AFM) measures degradation of
the system as a function of charge/discharge . In parallel, we employ Density Functional Theory
(DFT) andMolecular Dynamics (MD) simulations to understand the underlying fundamental processes,
ionic and electronic conduction, that govern interface performance and correlate them to interface
structure. We find an interesting concentration-dependent ionic conduction mechanism as well as
an advantageous restriction, but not elimination, of electronic conduction.
2:00 PM - *PM03.05.02
High-Performance Device Layers via Grain-Boundary and/or Interface Engineering and Controlled Self-Assembly of Nanostructures and Interfaces within Device Layers for Wide-Ranging Energy and Electronic Applications
Amit Goyal 1
1 , SUNY-Buffalo, Buffalo, New York, United States
Show AbstractFor many energy and electronic applications, single-crystal-like materials offer the best performance. However, in almost all cases, fabrication of single-crystal form of the relevant material is too expensive. In addition, for many applications, very long or wide materials are required, a regime not accessible by conventional single-crystal growth. This necessitates the use of artificially fabricated, large-area, polycrystalline, single-crystal-like substrates suitable for heteroepitaxial growth of the relevant advanced material for the electronic or energy application in question. These substrates are fabricated via large-scale grain-boundary and interface engineering. Heteroepitaxial growth of nanolaminate multilayers and devices on such substrates with engineered interfaces using a variety of deposition techniques such as pulsed laser ablation, sputtering, e-beam evaporation, MBE, MOCVD, and chemical solution deposition will be reported upon. Application areas that have been demonstrated via the use of such large-scale, artificial substrates include – high-performance devices based on oxide high-temperature superconductors, semiconductor materials (Si, Ge, GaAs, CdTe, Cu2O), ferroelectrics (BaTiO3), multiferroics (BiFeO3), etc. In addition, strain-driven self-assembly of second phase nanomaterials at nanoscale spacings has been demonstrated within device layers. Control of heteroepitaxy in lattice-mismatched systems and the effects of strain on self-assembly will be discussed. Such heteroepitaxial device layers on large-area, single-crystal-like artificial substrates are quite promising for a range of electrical and electronic applications.
2:30 PM - PM03.05.03
Engineering Super Thermal Insulation by Minimizing Interfacial Phonon Transmissions
Sumanjeet Kaur 1 , Sean Lubner 1 , Ravi Prasher 1
1 , Lawrence Berkeley National Lab, Berkeley, California, United States
Show AbstractHeating and cooling of buildings consumes ~15% of the total primary energy used by the United States. High-performance and cost-effective thermal insulation can significantly reduce cooling and heating loads, but currently all advanced insulation materials are too expensive for widespread commercial use and tend to be very mechanically weak. We are using nanoparticles and engineered nanoscale interfaces to manipulate heat transport to create economical and robust super thermal insulation.
Interfaces between materials disrupt heat flow by scattering phonons and reducing their mean free path (MFP). This effect is amplified in nanostructured materials due to their high interface densities, enabling them to achieve super low thermal conductivities while still retaining high solid volume fractions (>50%) that provide high mechanical strength. More generally, it was theoretically shown by Prasher et al.((R. Prasher et al. Physical Review B 74, 165413, 2006)) that phonon effective MFPs (and hence bulk nanoparticle bed thermal conductivity) can be reduced by 1) reducing the surface energy of contacting nanoparticles, 2) reducing the size of nanoparticles, and 3) increasing the degree of acoustic property mismatch among adjacent contacting nanoparticles. We are independently maximizing the effect of each of these parameters simultaneously to minimize thermal conductivity without destroying mechanical strength and while keeping manufacturing costs low.
2:45 PM - PM03.05.04
Manipulation of Bimetallic Nanoparticle Surfaces through Peptide-Enabled Synthetic Strategies
Nicholas Bedford 1
1 , Air Force Research Laboratory, Wright-Patterson AFB, Ohio, United States
Show AbstractThe catalytic properties of bimetallic nanoparticles can be directly correlated to the structure and composition at the nanoparticle surface. As such, considerable research efforts are focused on understanding bimetallic surface segregation and structure as a function of elemental composition, nanoparticle size, synthetic parameters and surface-ligand interactions. Similarly, interface interactions that occur during catalytic reactions have been shown to have profound effects on the resulting structure and composition, signifying the importance of in-situ characterization to better understand such phenomena. Clearly, a more thorough understanding of atomic-scale structure at the nanoparticle surface is paramount to elucidating structure/function relationships at the interface, which could be leveraged using rational synthetic routes if better understood.
To this end, peptide-enabled synthesis of nanoparticles has attracted much attention due to the capability to rationally optimize reactivity. This is accomplished through the complexity of functional chemistries found in peptides and their associated binding motifs to nanoparticle surfaces. Yet to fully understand relationships between the biotic/abiotic interface and resulting properties, a throughout understanding of structure/function relationships are required. Our group has demonstrated that sequence modification can be used to tune inorganic surface disorder using atomic-scale synchrotron characterization tools. More recently, we have leveraged peptide binding to manipulate bimetallic miscibility as well, with the goal of eventually using peptide-enabled synthetic methods to rationally design catalytic materials with optimal reactivity. This talk with summarize our work in this area, wherein X-ray absorption spectroscopy, high-energy X-ray diffraction, atomic pair distribution function analysis, and reverse Monte Carlo simulations are used in tandem to construct atomic-scale nanoparticle models, which can be used to assess sequence-dependent structure/function relationships at the bimetallic nanoparticle surface.
PM03.06/TC06.09: Joint Session I: Grain Boundaries
Session Chairs
Tuesday PM, November 28, 2017
Hynes, Level 2, Room 210
3:30 PM - *PM03.06.01/TC06.09.01
Quantifying the Commonalities in Structure and Plastic Deformation in Disordered Materials
Glenn Balbus 1 , Daniel Strickland 2 , Daniel Magagnosc 2 , Robert Ivancic 3 , Andrea J. Liu 3 , Dan Gianola 1
1 Materials Department, University of California, Santa Barbara, Santa Barbara, California, United States, 2 Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States, 3 Department of Physics, University of Pennsylvania, Philadelphia, Pennsylvania, United States
Show AbstractThe nonequilibrium nature of kinetically frozen solids such as metallic glasses (MGs) is at once responsible for their unusual properties, complex and cooperative deformation mechanisms, and their ability to explore various metastable states in the rugged potential energy landscape. These features coupled with the presence of a glass transition temperature, above which the solid flows like a supercooled liquid, open the door to thermoplastic forming operations at low thermal budget as well as thermomechanical treatments that can either age (structurally relax) or rejuvenate the glass. Thus, glasses can exist in various structural states depending on their synthesis method and thermomechanical history. Nanocrystalline (NC) metals, also considered to be far-from-equilibrium materials owing to the large fraction of atoms residing near grain boundaries (GBs), share many commonalities with MGs both in terms of plastic deformation and its dependence on processing history. Despite these similarities, the disorder intrinsic to both classes of materials has precluded the development of structure-property relationships that can capture the multiplicity of energetic states that glasses and GBs may possess.
Here, we report on experimental studies of MG and NC materials and novel synthesis and processing routes for controlling the structural state – and as a consequence, the mechanical properties. A particular focus will be on strategies for rejuvenation of disorder with the goal of suppressing shear localization and endowing damage tolerance. We also describe a microscopic structural quantity designed by machine learning to be maximally predictive of plastic rearrangements and further demonstrate a causal link between this measure and both the size of rearrangements and the macroscopic yield strain. We find remarkable commonality in all of these quantities in disordered materials with vastly different inter-particle interactions and spanning a large range of elastic modulus and particle size.
4:00 PM - *PM03.06.02/TC09.06.02
Predictive Equations of Motion for Grain Boundaries and Triple Junctions in Polycrystals
David Srolovitz 1 2 , Jian Han 1 , Luchan Zhang 1 3 , Spencer Thomas 1 , Kongtao Chen 1 , Prashant Purohit 2 , Yang Xiang 3
1 Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States, 2 Department of Mechanical Engineering and Applied Mechanics, University of Pennsylvania, Philadelphia, Pennsylvania, United States, 3 Department of Mathematics, University of Science and Technology, Hong Kong Hong Kong
Show AbstractThe equation of motion for grain boundaries (GB) and triple junctions (TJ) are commonly stated as the velocity is equal to the product of mobility and driving force, where the driving force may be associated with capillarity, jumps in the stored defect concentrations across the GB, etc. This class of equations of motion does not account for the microscopic mechanisms by which, we now know, GBs move; i.e., through the motion of disconnections (line defects within the GB). We first present a discrete disconnection model of GB migration; including how different classes of driving forces combine and how mobility depends on temperature and GB crystallography. We quantitatively validate this understanding through a series of atomistic simulations. Next, we derive a continuum equation of motion for GBs that is based on the underlying discrete disconnection dynamics mechanism. Finally, we provide a model for how TJs moves within the continuum disconnection dynamics framework, including several numerical examples of the motion of GBs delimited by TJs.
4:30 PM - PM03.06.03/TC06.09.03
Generalized Discrete Defect Dynamics—Application to Interfacial Defect Motion
Laurent Capolungo 1
1 , Los Alamos National Laboratory, Atlanta, Georgia, United States
Show AbstractInterfacial Defects (ID) refer to atomic arrangements delimiting the boundaries between distinct phases or material domains. IDs are found in bulk polycrystals in which diffusion-less transformations (twinning, phase changes) can be activated as an alternative or complement to dislocation glide mediated plasticity. This is the case of hexagonal close packed (hcp), face centered cubic (fcc), body centered cubic (bcc) and lower crystal symmetry materials in which such transformations can be activated depending on temperature, composition, and loading conditions. Twinning corresponds to a shear transformation while phase transformation is usually also dilatational. The work to be presented aims to study the effects of collective nucleation, motion and interaction of ID on the evolution of transformed domains (twins, transformed phase), associated internal stresses, and mechanical response. To this end a novel generalized discrete defect dynamics model, capable of simultaneously describing both dislocations and disclination, is proposed. Further, a series of didactive simulations will illustrate the kinematics of disclination motion and their implication on twin growth.
4:45 PM - PM03.06.04/TC06.09.04
Disconnection Mediated Grain Boundary Motion Explored by Atomistic Simulations
Chuang Deng 1
1 , University of Manitoba, Winnipeg, Manitoba, Canada
Show AbstractThe synthetic driving force method is a widely-used technique in molecular dynamics simulations to investigate the migration of grain boundaries. Its physical essence, however, has been under debate for quite some time for generating the driving force by artificially introducing some energy into the crystals. In this study, the elementary process governing the grain boundary motion under the driven motion method was explored by applying a varying synthetic driving force that increases from zero at a constant rate, which is in contrast to a constant driving force that is usually applied in past studies. With this method, it was found that a rate-controlling process, i.e., disconnection nucleation that has been reported before to dominate the physical grain boundary motion coupled to an applied shear, also operated for grain boundary motion caused by the synthetic driving force. Furthermore, the disconnection nucleation mediated process was also found to cause a strong size dependence and transitions of grain boundary motion modes at different temperatures. It is hoped that with this study, the synthetic driving force method in studying grain boundary motion can be used with more confidence in its physical essence and a universal mechanism can be proposed to explain grain boundary motion in materials despite how it is caused.
PM03.07: Poster Session
Session Chairs
Wednesday AM, November 29, 2017
Hynes, Level 1, Hall B
8:00 PM - PM03.07.01
Copper Segregation Affected Yielding in Nanotwinned Silver
Xing Ke 1 , Frederic Sansoz 1
1 , University of Vermont, Burlington, Vermont, United States
Show AbstractRecent studies have shown that small incoherent kink-like step defects in coherent twin boundaries play major roles on the strength and plasticity of nanotwinned face-centered-cubic metals and alloys. Understanding the small-scale mechanics of twin boundary defects under stress is critical for controlling their overall mechanical behavior; yet, the intrinsic yielding mechanisms associated with twin boundary defects remained unexplored. This poster will present large-scale hybrid Monte Carlo - molecular dynamic simulations used to investigate the effects of solute Cu segregation on the small-scale mechanics of nanotwinned Ag containing defective twin boundaries. Each simulated sample was segregated by annealing at 500 K with trace concentrations of 0.2 at%, 0.4 at%, 0.6 at% and 0.8 at% Cu, and subsequently deformed in pure tension up to 10% strain. Segregation simulations show that Cu atoms are strongly segregated to grain boundaries and kink-like twin boundary defects. Tensile simulations show that both twin stability and yield strength increase dramatically as the Cu content increases. Smaller bicrystal models made of only one kink defect were also segregated and sheared along three different directions. We find strong Cu segregation dependence of yield strength and underlying plastic deformation behavior in Ag bicrystals with a kink-like twin boundary defect. The yielding mechanism is observed to change from kink-step migration to kink-step splitting after segregation. The results offer new clues to further push the limit of strength in nanotwinned alloys.
8:00 PM - PM03.07.03
Characterization and Role of Interfaces in Stochastic Open-Cell Metal Foams
Dongfang Zhao 1 , Jayden Plumb 1 , Kristoffer Matheson 1 , Kory Cross 1 , Jonathan Lind 2 , Joseph Tucker 3 , Matthew Nowell 4 , Ashley Spear 1
1 , University of Utah, Salt Lake City, Utah, United States, 2 , Lawrence Livermore National Laboratory, Livermore, California, United States, 3 , Exponent, Menlo Park, California, United States, 4 , AMETEK, Draper, Utah, United States
Show AbstractCellular metals, or metallic foams, are an interesting example of hierarchical systems that derive their mechanical properties from a complex interaction of interfaces across multiple length scales, including both the grain scale and the topological scale of the foam structure. The vast majority of research on open-cell metal foams has focused on the topological scale (i.e. scale of interconnection among ligaments) and/or the characterization of macroscale mechanical properties. Recent work suggests that the grain scale also plays a crucial role in the mechanical behavior of open-cell metallic foams.
This talk will highlight several efforts to characterize and model the relationship among interfaces at both the grain and topological scale in open-cell aluminum foams. One effort focuses on the comparison of investment cast foam with duplicates produced via laser powder bed fusion. The full-field deformation of each foam is characterized using X-ray computed tomography measurements made in-situ during mechanical crushing. Differences in the macroscale crushing response among the foams are attributed to the type and sequence of ligament failure mechanisms, which are in turn influenced by the grain structure resulting from the two manufacturing methods. The foams produced by investment casting have a more ductile macroscale response than those produced by laser powder bed fusion. This can be explained in part by the fact that the investment-cast foam has a much lower density of grain boundaries per ligament than the foams produced by laser powder bed fusion. A parallel effort involves the development of an experimental procedure to reconstruct, for the first time, the 3D grain structure of open-cell metallic foam using high-energy X-ray diffraction microscopy (HEDM). Because of the sparsity of material, open-cell foams are especially challenging to characterize at the grain scale in 3D. A procedure is described for measuring portions of the foam using far-field HEDM and subsequently reconstructing the foam in a virtual manner. Finally, an ongoing modeling effort is described that will enable further exploration of the relationship among interfaces and mechanical behavior of stochastic open-cell metal foams. A special plug-in has been developed in the open-source software DREAM.3D that allows for generating grain-resolved stochastic open-cell foams. Virtual experiments are performed by varying both the grain structure and ligament structure of the foams and characterizing the influence on mechanical response of the foams.
All of the studies that will be described contribute to a research program that seeks to intelligently tailor the mechanical properties of open-cell metallic foams by understanding the relationships among process parameters and interface interactions across length scales.
8:00 PM - PM03.07.04
High Temperature Cyclic Sealability of Alumina-Containing Sealing Glass for Solid Oxide Fuel Cells
Sueng-Ho Baek 1 , Sung Park 1 , Jae Chun Lee 1 , Hyung Jun Kim 1
1 , Myongji University, Yongin Korea (the Republic of)
Show AbstractGlass–alumina (Al2O3) composites, namely borosilicate glass with alumina, have been studied widely to substrate materials for integrated circuits and microelectronic packaging. Alumina has been the dominant ceramic substrate material mainly due to its moderate strength and thermal conductivity. Solid oxide fuel cell (SOFC) industry requires a reliable seal that works for 40,000 hours at high temperatures above 700°C, and also overcomes the thermal stress problem induced by cyclic heating and cooling. Self-healing glasses, such as those made of compliant alkali-containing silicate glass have been proposed for the SOFC sealing glass. However, thermochemical and thermomechanical properties of self-healing alkali-silicate glasses are usually weaker than those of alkaline-earth silicate glasses. Thus, alumina-containing glass composites have been proposed for long-term cyclic sealing components for solid oxide fuel cells applications by present authors since the trivalent aluminum ions dissolved in alkali aluminosilicate glasses can act as network formers. It has been known that the rate-controlling step governing alumina dissolution is the diffusion of aluminum ions through the glass, so the dissolution of alumina into glass. In this work the dissolution of alumina in an alkali-silicate glass was investigated to improve the cyclic sealing performance. A glass composite seal containing proper amount of Al2O3 filler has survived more than 12,000 hours of leak test at 750°C for 31 consecutive thermal cycles. The long-term high temperature cyclic sealability was explained in terms of the viscosity and electrical conductivity of the sealing component as well as the phase transformation of the sealing glass-filler interface.
8:00 PM - PM03.07.05
Influence of Interfaces on the Efficiency of Thermophotonic Devices
Ivan Radevici 1 , Jonna Tiira 1 , Tuomas Haggren 1 , Toufik Sadi 1 , Jani Oksanen 1
1 , Aalto University, Espoo Finland
Show AbstractIt is commonly known that surfaces and interfaces of semiconductor materials have a significant role in controlling both the electronic and optical properties of semiconductor devices. Thus, the correct treatment of the surface states is very important in reproducible fabrication of appliances [1].
In this communication, we study how surface states affect the thermophotonic energy transport in double diode structures (DDS), which are made of a heterojunction LED grown on top of homo- or heterojunction photodiodes (PDs) [2-3]. The devices are based on epitaxial GaAs structures with AlGaAs or GaInP barriers grown by either MBE or MOCVD and processed by several consecutive lithography and wet etching steps to define DDSs of different sizes and to deposit n- and p-contacts using standard contact metallization schemes. For different material groups and combinations a set of suitable selectively etching acid solutions were used. The main characterization of the devices was done in a 3-point probe setup where the IV characteristics of the LED were measured while simultaneously measuring the IV characteristics of the photodiode. To estimate the photon emission efficiency we use the IV results to determine the coupling quantum efficiency (CQE) defined as the ratio between PD and LED current [2], [3].
In this work three types of interfaces are considered: a) the reflective interfaces and their effect on optical losses and transport, b) interface states and their influence on recombination rate, and c) mesa edge surface states resulting from the native oxides generating undesirable energy levels within GaAs band-gap and reducing performance of the LED and the PD. We report how different metallization schemes and resistivity of the contacts affect the CQE, and fit experimental IV curves obtained for different contact materials to the ABC recombination model. Interface states between the epilayers are studied experimentally by comparing the efficiency of the DDSs with AlGaAs and GaInP barriers, having different interfaces to GaAs. Results on GaAs/AlGaAs and GaAs/GaInP interfaces were also compared to theoretical predictions. Edge surface states are studied by using different passivation techniques allowing to remove surface oxides (e.g., ammonium sulfide passivation), or to protect DDS side walls from contact with air, having an added value of light reflection from the structures edges (e.g. PECVD deposition of silicon nitride). Also, experimental IV curves are analyzed within the Shockley-Read-Hall recombination model, allowing to estimate the influence of interface states and to propose ways to reduce the resulting non-radiative recombination. Possibilities to improve the CQE of the devices and to reach the EL cooling regime by modification of surface properties are discussed.
[1] A. Baca, C. Ashby, Fabrication of GaAs Devices. IET, 2005.
[2] J. Tiira et al., Proc of SPIE 2017, p. 1012109.
[3] A. Olsson et al., IEEE Trans. Electron Devices, v. 63, p. 3567, 2016.
8:00 PM - PM03.07.06
Preparation of Hollow Nanochanneled-Silica Nanospheres by Sacrificial Copolymer Nanospheres and Surfactant Nanocylinders
Myoeum Kim 1 , Yong Ku Kwon 1
1 , Inha University, Incheon Korea (the Republic of)
Show AbstractNovel monodisperse, well-defined hollow nanochanneled-silica nanospheres were prepared using copolymeric template. Positively-charged, monodisperse poly(styrene-co-butyl acrylate-co-[2-(methacryloxy)ethyl]trimethyl ammonium chloride) (PSBM) nanospheres with smooth surfaces and a very narrow size distribution were synthesized by surfactant-free emulsion copolymerization and freeze drying. These PSBM nanospheres were used as a sacrificial core material. The silica shell phase was deposited on the surface of the PSBM core template by using a charge-charge interaction between the negatively-charged silica precursors, associated with a surfactant compound and the positively-charged polymer nanospheres. The polymer core part and the structure-directing surfactant were selectively removed by thermal treatment, and hollow nanochannels in the silica shell phase was simultaneously induced in the solid rearrangement process at high temperature. The unique channel structure and the facile accessibility to the hollow interior space were carefully investigated by many characterization techniques.
8:00 PM - PM03.07.07
Analysis of the Interface and Strain for T2SL Depending on the Thickness of the Strain Compensation Layer
Minhyuk Choi 1 2 , Seungwoo Song 1 , In-young Jung 1 , Sang Jun Lee 1 , Jaesuk Kim 2 , Moondeok Kim 2 , Chang Soo Kim 1
1 , Korea Research Institute of Standards and Science, Daejeon Korea (the Republic of), 2 , Chungnam National University, Daejeon Korea (the Republic of)
Show AbstractThe infrared detector using InAs/GaSb Type 2 Superlattice (T2SL) has received widely attention as a high-performance quantum infrared detection material that can replace the well-known infrared detector HgCdTe (MCT), InSb and quantum well infrared detectors (QWIPs). In particular, because the effective mass of the electrons is relatively larger than that of conventional quantum infrared detector, the transmission current between the bands could be reduced. And the lower Auger recombination rates in T2SL detectors lead to higher operating temperature and better detection performance. Also, the T2SL detector can operate in wide wavelength region from a short wavelength to a long wavelength infrared by changing the thickness or composition of the materials in superlattice structure.
The T2SL is synthesized by a well established Molecular Beam Epitaxy (MBE) alternating each InAs and GaSb layers. Although they have ~0.63% of the small lattice mismatch between the layers, a strain from lattice mismatch can be introduced at the interface depending on deposition conditions. Hence, it is difficult to effectively compensate the strain without changing the structure. Indeed, inserting of thin InSb layer, called the strain compensation layer, between InAs and GaSb could effectively compensate the accumulated tensile strain at the interfaces because it makes the lattice constant changed. When the GaSb layer is inserted in-between for strain compensating effect, it could change a cut-off wavelength which we do not want. Thus, In this study, we specifically focus on the strain effect to InAs/GaSb superlattice depending on thickness of the strain compensation layer less than 1 monolayer (ML)
We deposited 4 types of T2SL photodetector with InAs (10ML)/InSb/GaSb (10ML) grown by MBE. Each of them has a different thickness of InSb strain compensation layer 0ML, 0.3ML, 0.6ML and 1ML. To analyze their interface and difference of strain more accurately, high-resolution X-ray diffractometry (HRXRD) equipped 4-bounce Ge(220) monochromator and TEM (Transmission electron microscopy) were used. By comparison the XRD curve with the simulation results, we could observe the change of the interface thickness for each samples. Additionally, through the results of the FWMH (full width half maximum) of 1st order peak and peak separation between the substrate and 0th order peak, the thickness of the strain compensation layer for minimizing the strain was found. PL (photoluminescence) measurements were also used to confirm the change of the optical characteristics and cut off wavelength depending on the thickness of the strain compensation layer.
8:00 PM - PM03.07.09
A Novel Lateral Growth Technique to Deposit SiGe Thin Films on Si with Uniaxial Strain and Low Threading Dislocation Density
Andrew O'Reilly 1 , Nate Quitoriano 1
1 , Materials Engineering, McGill University, Montreal, Quebec, Canada
Show AbstractStrained Si1-xGex and Ge have superior mobilities over traditional, unstrained channels. These strained materials have been proposed as the next evolution to improve CMOS performance. Currently, uniaxially compressive strained Si1-xGex channels are integrated into commercial integrated circuits by substituting SiGe as the source and drain material. Given the larger lattice constant of relaxed SiGe, the source and the drain exert a compressive stress on the channel in between. Techniques to introduce uniaxial strain without the use of external stressors have been proposed by the selective relaxation of a pseudomorphic SiGe layer on Si. These techniques, though successful at fabricating uniaxial-strained SiGe channels, require multiple, and sometimes complicated steps, such as substrate transfer and bonding as well as ion implantation.
A novel lateral liquid-phase epitaxy (LLPE) technique was developed to deposit a blanket epilayer of asymmetrically strained Si97.4Ge2.6 on Si (001) in a single step. Epitaxial growth was initiated by traditional vertical LPE. The thickness of the epilayer was greater than the critical thickness for misfit dislocations, which allowed the misfit strain to be relieved by the nucleation of an orthogonal network of misfit dislocations. The epilayer was then grown laterally in the [110] direction and the film thickness was kept below the critical thickness for dislocation nucleation, and above the critical thickness for dislocation glide. This promoted the glide of misfit dislocations along the [110] growth direction, from the initial growth region into the laterally grown region, which creates an array of parallel misfit dislocations. In this way, the separate critical thicknesses for dislocation nucleation and dislocation glide are observed.
The array of parallel misfit dislocations results in asymmetric strain relaxation, where the film is fully strained in the [110] direction and 31 % strain relaxed in the [11̅0] direction. In addition, the inhibition of dislocation nucleation favours the formation of long misfit dislocations by dislocation glide, which reduces the threading dislocation density from 105/cm2 in the initial growth region to 103/cm2 in the lateral growth region.
8:00 PM - PM03.07.10
High-Throughput Computational Design of Heterojuctions for Electronic Devices
Keith Butler 1 , Aron Walsh 2 3
1 , University of Bath, Bath United Kingdom, 2 Materials Science, Imperial College London, London United Kingdom, 3 , Yonsei University, Seoul Korea (the Republic of)
Show AbstractThe design and control of interface structures is a critical concern in the fabrication of electronic devices in fields as diverse as photovoltaics, solid-state batteries, fuel cells, and non-volatile memory to name but a few. However, rational procedures for choosing optimal combinations of materials are hampered by the complexity of interface structures. Experimentally it is notoriously difficult to characterise interfaces at an atomic level, theoretical modelling of interfaces necessitates the consideration of a large configurational and compositional space, making screening procedures difficult.
The rapid progress in performance of solar cells based on hybrid halide perovskites means that devices based on these materials have reached a stage where research interest can now focus on development of robust technology. One of the key questions relating to these (and indeed any) devices is their lifetime and stability, which in turn is often influenced by the quality of interfaces and junctions within the device.
We present a low-cost, high-throughput methodology, based on parameters that can be accessed experimentally or theoretically, for predicting stable electronically matched interface combinations [1-3]. The simplicity of the approach means that it can be applied to high-throughput screening with minimal computational cost. We develop a figure of merit for interfaces in solar cells and specifically apply the procedure to search for semiconductor contacts for halide perovskites. The screening allows us to predict several new structurally coherent cell architectures. Furthermore, we demonstrate the application of this methodology to design in other important technological fields – porous electronic devices and heterojunction oxide photocatalysts.
[1] KT Butler, Y Kumagai, F Oba, A Walsh Screening procedure for structurally and electronically matched contact layers for high-performance solar cells: hybrid perovskites J. Mater. Chem. C, 6, 1149 (2016)
[2] JK Bristow, KT Butler, KL Svane, JD Gale, A Walsh Chemical bonding at the metal–organic framework/metal oxide interface: simulated epitaxial growth of MOF-5 on rutile TiO2 J. Mater. Chem. A, 5, 6226 (2017)
[3] KT Butler, CH Hendon, A Walsh Designing porous electronic thin-film devices: Band offsets and heteroepitaxy Faraday Dissc. In Press (2017)
8:00 PM - PM03.07.11
Optimizing the ORR Activity in Hetero-Structured LSC-113 and LSC-214 Perovskites via Combinatorial Approach
Dogancan Sari 1 2 , Ziya Torunoglu 1 2 , Yunus Kalay 1 2 , Tayfur Ozturk 1 2
1 Metallurgical and Materials Engineering, Middle East Technical University, Ankara Turkey, 2 , ENDAM, Center for Energy Storage Materials and Devices, Ankara Turkey
Show AbstractPerovskite based mixed conductive oxides are commonly used oxygen catalysts in solid oxide fuel cells, catalytic reforming of carbon dioxide and oxygen separation membranes. In recent years, the introduction of dissimilar interfaces in nanocomposite perovskites resulted in improved activity in ORR/OER. Of these, the dissimilar interfaces between La1-xSrxCoO3-d (LSC-113) and (La1-ySry)2CoO4+d (LSC-214) is particularly noteworthy as they proved to be an efficient catalyst for ORR in intermediate temperature solid oxide fuel cells. Although the beneficial effect of these interfaces is quite well-known, the full potential of these hetero-structures have not yet been explored. There are two critical parameters to explore in such composites, the scale of structure and the volume fractions of phases, both of which influences the density of dissimilar interfaces. In this study, a combinatorial approach was used so as to optimize LSC113-LSC214 nanocomposite for improved ORR activity in the temperature range from 700 - 400 oC. This was achieved in a sputter deposition system where LSC113 and LSC214 were co-sputtered onto substrates spatially distributed on a plane above, each with a different resultant phase mixtures. Impendence spectroscopy measurements in symmetric cells indicate that the phase mixtures close to LSC113:LSC21 = 50:50 give the most favorable results.
8:00 PM - PM03.07.12
Design and Processing of Alumina Mineral Plates Composites for Ballistic Nacre Alumina Structures
Aisha Haynes 1 2 , Calvin Lim 2 , David Rydzewski 1 , Lauren Morris 1
1 , Armaments Graduate School, U.S. Army ARDEC, Picatinny Arsenal, New Jersey, United States, 2 Armaments Engineering Analysis and Manufacturing Directorate, U.S. Army Research Development and Engineering Center, Picatinny Arsenal, New Jersey, United States
Show AbstractNacre is a hierarchical multi-composite matrix consisting of plate-like structures stacked up similar to brick and mortar. When impacted with a projectile this type of structure is expected to reduce the overall shock loading into the system as a consequence of variations in structural stiffness between the composite plates and the organic interlayers. Bio-mimicked Nacre derived from alumina as the base ceramic is also shown to have increased fracture toughness over an alumina monolith. One challenge to building the Nacre alumina structure is the design and processing of the composite mineral plates which should be comprised of 90% alumina nanoparticles and roughly 10% organic binder. In order for these plates to accurately mimic the nacre mineral plates they must also emulate aspect ratios on the order of 1:10 to 1:20. This paper will discuss the design and processing of nacre-alumina plates for studies into the impact behavior of Nacre Alumina composites.
8:00 PM - PM03.07.13
Environmental and Curvature Responsive PE Brushes
Guang Chen 1 , Siddhartha Das 1
1 , University of Maryland, College Park, Maryland, United States
Show AbstractPolyelectrolyte (PE) brush grafting on the solid-liquid interfaces renders tremendous functionalities to nanofluidic systems, ranging from nanoactuator to ion transport manipulation. Therefore it is essential to understand thermodynamics and electrostatics of such PE grafted systems. In this work, we extend our well-established study on planar PE brush systems to PE brushes grafted onto cylindrical and spherical interfaces, and we focus on the stimuli-responsive configuration for such grafted systems. Theoretical models for the monomer density distribution and height of the bent PE brushes are developed as functions of grafting density, curvature, and salt concentration. We show that the PE brush will be shorter for a convex interface with brush facing outward, while it will be taller for a concave interface with brush facing inward. We have determined critical parameter phase spaces for cylindrical and spherical grafted systems where the PE chains attain partial brush partial coil configuration. Reversely the environmental-responsive change in PE brush systems will also lead to an impact on the morphology of the grafted interface. We have also demonstrated with numerical analysis that grafting PE brush can massively enhance the electroosmosis in nanochannels. Understanding these issues will be pivotal in designing optimal salt concentration indicator and developing novel functionalities that can potentially be applied in several disciplines in nanotechnology and biochemical engineering. It will also provide important clues to decipher the behavior of a myriad of biological and chemical systems (e.g., PE-grafted nanoparticles, sheathed bacteria, phage viruses, etc.) that bear certain geometric and physical resemblances to the PE-grafted nanochannel system.
8:00 PM - PM03.07.14
Determination of the Interface Properties for p-CZTSe/n-Si Nanowire Heterojunction Diode
Ozge Bayrakli 1 2 , Makbule Terlemezoglu 1 5 , Hasan Güllü 1 , Dilber Yildiz 3 , Tahir Colakoglu 1 , Emre Coskun 4 , Mehmet Parlak 1
1 , Middle East Technical University , Ankara Turkey, 2 Physics, Ahi Evran University, Kirsehir Turkey, 5 Physics, Namik Kemal University, Tekirdag Turkey, 3 Physics, Hitit University, Corum Turkey, 4 Physics, Canakkale Onsekiz Mart University, Canakkale Turkey
Show AbstractThe one-dimensional semiconductors such as Si-nanowires are very popular materials for the optoelectronic applications due to their noticeable physical properties. The capability of light trapping increases the absorbance of the device surface and enhances the optoelectronic properties. On the other hand, interface state properties of Si-nanowire junction strongly influence the performance of Si nanowire photovoltaic devices. In this work, the interface state density (Dit) of p-CZTSe/n-Si nanowire heterojunction diode was investigated. The fabrication of Si nanowires having 3.0 nm length was performed by AgNO3 and HF solution based metal-assisted etching process on n-type (111) mono-crystalline 600 µm Si wafers with the resistivity value of 1 - 3 (Ω.cm). The heterojunction diodes were constructed by depositing 600 nm p-CZTSe thin film layer using physical vapor deposition technique onto these fabricated Si nanowires. Frequency dependent capacitance-voltage (C-V) measurements were carried out. It was seen that there was a sharp decrease in capacitance when the frequency was increased from 10 kHz to 1MHz. The distribution of localized interface state density (Dit) could be so influential for this observed fluctuation. In order to determine the interface state density (Dit), both high-low frequency capacitance (CHF-CLF) and Hill-Coleman methods were used.
8:00 PM - PM03.07.16
Structure, Chemistry and Properties of CuO-xCu2O Quasi-Liquid Grain Boundary Layer of CaTiO3-NdAlO3 Based Dielectric Ceramics
Li-jin Cheng 1 2 , Zong-lian Huang 2 , Jia-Min Wu 1 , Shaojun Liu 2
1 State Key Laboratory of Material Processing and Die and Mould Technology, Huazhong University of Science and Technology, Wuhan China, 2 State Key Laboratory for Powder Metallurgy, Central South University, Changsha, Hunan, China
Show Abstract0.7CaTiO3-0.3NdAlO3 (CTNA) ceramics are widely used as resonators and filters in the wireless communication technology. However, abnormal grain growth and crystal defects can be induced in CTNA ceramics due to elevated sintering temperature and lengthened soaking time. They are believed to significantly deteriorate the microwave properties. Our recent findings show that a small amount of CuO addition obviously promotes the densification kinetics and decrease the maximum densification rate temperature of CTNA ceramics. Although it is believed that the appearance of quasi-liquid layers during the early sintering stage promotes mass transport by short-circuit diffusion, the formation mechanisms is still not clear.
In the present paper, in a combination with isothermal sintering, aberration-corrected TEM with EDS, and water quench treatment, the structure, chemistry, and properties of CuO-xCu2O grain boundary quasi-liquid layers in 0.7CaTiO3-0.3NdAlO3 microwave ceramics doping with various CuO contents are identified and clarified in detail.It is found that instable eutectic CuO and Cu2O quasi-liquid phase films, which are continuously distributed along the grain boundaries due to the decomposition of CuO at 900°C in the early stage of sintering, lead to the viscous flowing of grains, promote the grains rearrangement, and provide a short-circuit diffusion path for mass transport. Especially, the dominant sintering mechanism is changed from the viscous flow to the grain boundary diffusion as Cu+ is oxidized to Cu2+. As CuO doping content is below 0.25wt%, Cu2+ ions substitute Ca2+ ions, inducing the lattice volume shrinkage. In contrast, excess Cu2+ ions replace Al3+ ions, bringing the lattice volume expansion. The induced crystal structure changes can be related to the dielectric loss in microwave frequency. In summary, dense CTNA ceramics (>97%) doped 0.05-0.1wt% CuO that are successfully sintered at a significantly shortened soaking time exhibit significantly enhanced microwave properties: εr = 44.6 ~ 45, Qf = ~ 40000 GHz, and τf = 5 ~ 6 ppm/°C.
8:00 PM - PM03.07.17
Assessment of GeSn Surface Wet Treatment Prior to Atomic Layer Deposition of High-k Dielectrics
Mohamed Aymen Mahjoub 1 2 , Thibault Haffner 1 2 , Joris Aubain 3 , Jean Michel Hartmann 3 , Gérard Ghibaudo 4 2 , Sébastien Labau 1 2 , Bernard Pelissier 1 2 , Franck Bassani 1 2 , Thierry Baron 1 2 , Bassem Salem 1 2
1 , LTM/CNRS, Grenoble France, 2 , Université Grenoble Alpes, Grenoble, Rhône-Alpes, France, 3 , CEA/LETI, Grenoble, Rhône-Alpes, France, 4 , IMEP/LAHC, Grenoble France
Show AbstractGermanium−tin (GeSn) alloys are promising for use in nano-electronics. Smaller effective masses for charge carriers in GeSn make it a material of choice for low power devices such as tunnel-FETs and high mobility MOSFETs. Moreover, GeSn exhibits a direct band gap when the Sn concentration exceeds a value of 6.5 at.%, making this material very promising for optical applications. However, the applications of GeSn are limited by the ability to deposit a thin high-k dielectric layer with a well-controlled and high interface quality.
Atomic layer deposition (ALD) is the most appropriate technique for high-k dielectrics layers with a good control of thickness and uniformity. Therefore, the major obstacle in using high-k materials is the high-interface trap density (Dit) caused by rough interfaces, partial and unsatisfied chemical bonds and impurities. Wet treatment of the GeSn surface is crucial to reduce these interfaces states. To our knowledge, no conventional wet treatment of GeSn exists up to now. Thus, in this work, ten different wet-etching protocols using HF, HCl, NH4OH, Pirhana and (NH4)2S were compared. The surface morphology was characterized using atomic force microscopy (AFM). Then, Al2O3 layers were deposited at 250°C. The chemical composition of the Al2O3/GeSn stacks, as well as the interface between the GeSn surface and Al2O3 were investigated by parallel angle-resolved X-ray photoelectron spectroscopy (pARXPS). Then, capacitance-voltage measurements were performed in order to extract the Dit. We conclusively showed that the wet treatment has a considerable influence on the quality of the Al2O3/GeSn interface.
8:00 PM - PM03.07.18
ZnO and ZnS Microstructures as Flame Retardant Coatings on Cotton Fabrics
Yiwei Wang 1 , Ruiqing Shen 2 , Qingheng Wang 2 , Yolanda Vasquez 1
1 Department of Chemistry, Oklahoma State University, Stillwater, Oklahoma, United States, 2 Department of Fire Protection & Safety, Oklahoma State University, Stillwater, Oklahoma, United States
Show AbstractFires cause approximately 1.3 million accidents annually that result in 3,257 deaths, 15,775 injuries and an estimated $11.6 billion in direct property losses. Flame-retardant materials play an important role in reducing or preventing damage caused by fires. In this study, we report that ZnO and ZnS microparticles and rods show promising behavior as flame-retardant materials when coated onto cotton fabrics. ZnO and ZnO/ZnS rods were nucleated and grown onto cotton using a multi-step hydrothermal synthesis. Properties such as heat release rate, total smoke release and mass loss rate of the materials were tested using a cone calorimeter. ZnO and ZnO/ZnS rods were able to reduce the heat release rate and total smoke release from 117.77 kW/m2 and 18.3 m2/m2 to about 70 kW/m2 and 6 m2/m2, respectively. The improved fire growth rate (FIGRA) index of these coatings indicates that there is potential for use these materials as fire-retardants.
8:00 PM - PM03.07.19
On the Role of the Matrix-Precipitate Interface in Precipitate Hardened Mg Alloys—An Atomistic Study
Aviral Vaid 1 , Julien Guénolé 1 , Sandra Korte-Kerzel 2 , Erik Bitzek 1
1 , University of Erlangen-Nuremberg, Erlangen Germany, 2 , RWTH Aachen University, Aachen Germany
Show AbstractThe mechanical properties of Mg-Al alloys are greatly influenced by the complex intermetallic Mg17Al12, which is the most dominant precipitate found in this alloy system. In this work, we present our recent atomistic studies of basal edge and 30 degree dislocations interacting with Mg17Al12 precipitates of different sizes (D), shapes, orientations, and inter-precipitate spacing (L). The critical resolved shear stress to pass an array of precipitates was found to follow the usual (1/D+1/L) dependency, while at the same time not being significantly influenced by matrix-precipitate orientation relationship, or the relative orientation between the slip planes in the matrix and precipitate. The dislocation passes the precipitate in a manner similar to the Orowan mechanism. However, no remaining dislocation loops were observed. More detailed investigation uncovered that the dislocation loop was absorbed at the interface while leaving a step at the matrix-precipitate interface. The findings here are discussed in the context of changes in dislocation stress field after dislocation absorption, dislocation content at the interface, and more generally the importance of interfaces on precipitation strengthening.
8:00 PM - PM03.07.20
Investigating the Local Fatigue Properties of Materials and Interfaces
Benoit Merle 1
1 , Friedrich-Alexander University, Erlangen, Erlangen Germany
Show AbstractFor the first time, the local fatigue properties of ultrafine-grained copper were investigated on the micrometer-scale up to the high cycle fatigue (HCF) range, relying only on widely available nanoindentation hardware. This breakthrough was achieved by combining the widely used micropillar compression method with the fast actuation (40 Hz) provided by the continuous stiffness measurement (CSM) module, originally intended for pyramidal nanoindentation. Cyclic testing was performed at constant nominal stress amplitude for up to several million (3.10^6) cycles. The resulting strain amplitude was directly recorded and the plastic strain was evaluated from the phase angle measured by the lock-in amplifier during testing. Defining a threshold for strain amplitude decrease as failure criterion further enabled the determination of S-N curves. The fatigue behavior of the tested ECAP copper micropillars was found to be dominated by cyclic softening, which is in line with previous macroscopic observations on similar samples. The calculated plastic strain amplitude also matches the literature data closely. Generally, the new method has a great potential for studying the local cyclic effects taking place at interfaces in complex micro-architectured materials.
8:00 PM - PM03.07.21
From Hollowing of Metal Nanoparticles to "Hollowing" of Thin Metal Films
Nimrod Gazit 1 , Leonid Klinger 1 , Gunther Richter 2 , Eugen Rabkin 1
1 Department of Materials Science and Engineering, Technion–Israel Institute of Technology, Haifa Israel, 2 , Max Planck Institute for Intelligent Systems, Stuttgart Germany
Show AbstractHollow metallic nanostructure (nanotubes, nanoparticles, etc.) attract great deal of attention due to their possible applications in various fields of nanotechnology (drug delivery, energy production and storage, catalysis, etc.). One of the synthesis methods of hollow nanostructures relies on Kirkendall effect during interdiffusion in the core-shell nanostructures. This method, however, requires high homological temperatures or high concentration of lattice defects ensuring bulk diffusion distances comparable with the nanostructure’s size.
In this study we report on the synthesis of hollow Au nanoparticles (NPs) on various substrates and at low homological temperatures at which only the short-circuit diffusion is operational. Our method provides higher microstructure stability of the hollow structure and allows “sculpturing” of the size and shape of internal pore.
In order to study the formation kinetics of the hollow structures we used the energy filtered transmission electron microscopy (EFTEM) method. Using this method, combined with other microscopy techniques we were able to characterize the mass transfer mechanism at different stage of the hollowing processes and to develop a quantitative model that shows a good agreement with our experimental data.
Applying our method to the nanoparticles of the Ag-Au alloy resulted in partially agglomerated thin Au films with high area density of holes. The decreased thermal stability of the Au film is attributed to the accelerated thermal grooving process. Based on our latter results we concluded that chemical driving forces have to be taken into account in the analysis of thermal stability of multicomponent thin films.
8:00 PM - PM03.07.22
Hollowing of Al-Au Nanoparticles by Intermetallic Phase Formation
Nimrod Gazit 1 , Gunther Richter 2 , Leonid Klinger 1 , Andriy Gusak 3 , Eugen Rabkin 1
1 Department of Materials Science and Engineering, Technion–Israel Institute of Technology, Haifa Israel, 2 , Max Planck Institute for Intelligent Systems, Stuttgart Germany, 3 Department of Physics, Cherkasy National University, Cherkasy Ukraine
Show AbstractThe Al-Au couples are widely employed in the microelectronic industry in various wire bonding assemblies. During the high temperature working conditions the interdiffusion in the contact zone leads to the formation of intermetallic phases. Formation of such phases has strong implication over the properties and may lead to the bond failure due to void formation. Here we show that voids form in sub-micron Al-Au core-shell particles even at relatively low temperature.
We study the intermetallic phase formation in Al-Au particles. First, we produced an array of Al particles employing the solid state dewetting process of Al film deposited on sapphire substrate in the molecular beam epitaxy tool, followed by in situ annealing. Then, Au layer was deposited on the particles followed by annealing at low homological temperature. During the latter annealing, the intermetallic phases formed in the particle, which resulted in formation of larger irregularly-shaped internal hole. The hollowing process and its kinetics were studied by X ray diffraction, and a combination of scanning and transmission electron microscopies.
Symposium Organizers
Ying Chen, Rensselaer Polytechnic Institute
Erik Bitzek, University of Erlangen-Nuremberg
Maria Teresa Perez Prado, IMDEA Materials Institute
David Rowenhorst, U.S. Naval Research Laboratory
PM03.08: Interface-Mediated Damage Mechanisms
Session Chairs
Wednesday AM, November 29, 2017
Sheraton, 3rd Floor, Commonwealth
8:15 AM - *PM03.08.01
Dislocation Interactions with Grain Boundaries Drive Hydrogen-Induced Intergranular Failure
Kaila Bertsch 1 , Shuai Wang 2 , Ian Robertson 2 3
1 Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 2 Department of Engineering Physics, University of Wisconsin–Madison, Madison, Wisconsin, United States, 3 Department of Materials Science and Engineering, University of Wisconsin–Madison, Madison, Wisconsin, United States
Show AbstractThe presence of hydrogen in Ni and Fe can cause a transition in failure mode from ductile transgranular to brittle intergranular. This transition is generally explained in terms of a hydrogen reduction of the grain boundary cohesive energy. However, this assumes the plasticity that occurs prior to the failure event has no role in the transition. Recent simulations have shown that the hydrogen concentration achievable on grain boundaries under standard thermal charging conditions is insufficient to reduce the grain boundary cohesive energy sufficiently to make it the weakest link in the system. This raises the question of what is the additional driving force behind the transition in failure mode. By taking a holistic approach and considering the dislocation interactions with the grain boundary, the disorder introduced by the accommodation and emission of dislocations in the process of strain transfer, and the transport of hydrogen by the dislocations into and away from the grain boundary, it will be demonstrated that the increased hydrogen accumulated at the grain boundary as well as the deformation-induced disorder associated with the plasticity together make the grain boundary the weak link in the system. That is, the hydrogen-induced transition in the failure mode is driven by the hydrogen-accelerated plasticity processes although the ultimate failure is caused by a decohesion event.
8:45 AM - PM03.08.02
In Situ Stable Fracture of Ceramic and Metal Ceramic Interfaces on the Micron Scale
Giorgio Sernicola 1 , Thomas Britton 1 , Finn Giuliani 1
1 Department of Materials, Imperial College London, London United Kingdom
Show AbstractThe fracture toughness of ceramics is often dominated by the structure of their grain boundaries. Our capacity to improve the performance of ceramic components depends on our ability to investigate the properties of individual grain boundaries. This requires development of new fracture testing methods providing high accuracy and high spatial resolution. Recently, several techniques have been developed using small scaled mechanical testing, based within a nanoindenter, using a variety of tip and sample geometries, including: micropillar compression, microcantilever bending and double-cantilever compression. However, the majority of the published work relies on load-displacement curves for the identification of crack initiation and the geometries can result in a complex analysis of force distribution and stress intensity factor.
Our approach uses a double cantilever geometry to obtain stable crack growth and we calculate the fracture energy under a constant wedging displacement. The tests are carried out within an SEM, this has two benefits: the sample is well aligned for a controlled test and images are recorded during the test for later analysis. Crucially this allows us to use beam deflection and crack length rather than critical load to measure fracture toughness. Our tests have proved it is possible to initiate and stably grow a crack in a controlled manner in ceramic materials for several microns. This approach has been validated on SiC where it gives a good approximation of the surface energy and then extended to SiC bi-crystals along with Ni-Al2O3 interfaces where crack blunting and bridging mechanism can be observed and measured.
9:00 AM - *PM03.08.03
Microscale and Mesoscale Mechanical Testing of Oxidised Grain Boundaries in Nickel Based Alloys
David Armstrong 1 , Angus Wilkinson 1 , Roger Reed 1 , David Collins 1 , David Crudden 1 , Sergio Lozano-Perez 1 , Judith Dohr 1 , Thierry Couvant 2 , Andre Nemeth 1
1 , University of Oxford, Oxfordshire United Kingdom, 2 , EDF, Moert-Sur-Loing France
Show AbstractThe oxidation and subsequent failure of grain boundaries is well known to be component life limiting in a wide range of nickel based alloys for both aerospace and nuclear applications. However understanding both the mechanisms by which oxides grow and fail and the boundaries individual strength is extremely challenging experimentally. Multiscale models informed by experiments are needed to both predict component failure through grain boundary fracture as well as developing new alloys with better oxidation resistance. Here two methods, one at the micro and one at the mesoscale, for studying the effects of oxidation on the mechanical properties of grain boundaries will be reported.
Alloy600 is a widely used material in pressurised water reactors. The mechanical response of oxidized grain boundaries have been investigated by performing microcantilever bend tests. It was found that whilst failure can proceed along the oxide-metal interface not all oxidized grain boundaries exhibit intergranular failure. The presence of an external surface oxide has been identified as playing a crucial role in influencing the mechanical response. By removing the surface oxide, using a focused ion beam, tests were performed on the same grain boundaries with and without a surface oxide layer, and showed that surface oxides can effect fracture behavior. Taking into account the effect of the surface oxide on microcantilever tests, it was possible to predict the experimentally observed behavior via realistic cohesive damage finite element simulations, which further underline the experimental observations For the cohesive law applied along the IG oxide-metal interface, the damage initiation stress σf was found to be 575 MPa and the opening displacement was Δf = 5 nm. This corresponds to an interfacial fracture energy G of 1.44 J m− 2 for the oxide/metal interface and an estimated fracture toughness 0.5 MPa m0.5 which is in good agreement with literature data.
In the second example a mesoscale (1mm x 1mm gauge cross section) electro-thermomechanical testing (ETMT) sample has been used to study the loss of ductility in the high strength polycrystalline superalloy 720Li in air between room temperature and 1000 °C. Tensile ductility is influenced profoundly by the environment, leading to a pronounced minimum at 750 °C. A relationship between tensile ductility and oxidation kinetics is has been identified. The physical factors responsible for the ductility dip are established using SEM EDX and the analysis of electron backscatter diffraction patterns. Embrittlement results from internal intergranular oxidation along the γ -grain boundaries, and in particular, at incoherent interfaces of the primary γ′ precipitates with the matrix phase. These fail under local microstresses arising from the accumulation of dislocations during slip-assisted grain boundary sliding. Above 850 °C, ductility is restored because the accumulation of dislocations at grain boundaries is no longer prevalent.
10:00 AM - *PM03.08.04
On the Interaction of 3D Crack Surfaces with Grain Boundaries in Polycrystalline Materials
Ashley Spear 1 , Brian Phung 1 , Kyle Pierson 1 , Jacob Hochhalter 2 , P. Thomas Fletcher 1
1 , University of Utah, Salt Lake City, Utah, United States, 2 , NASA Langley Research Center, Hampton, Virginia, United States
Show AbstractAdvancing the state of materials design and structural prognosis will inevitably require improved predictive capabilities for the evolution of microstructurally small fatigue cracks (MSFCs). Specifically, such predictive capabilities should be able to simulate the interaction among crack surfaces and grain boundaries, which should essentially be informed by fundamental crack-driving mechanisms. This talk will describe recent efforts to improve understanding of MSFC driving mechanisms in 3D and will then describe a finite-element-based modeling framework that accommodates crack growth based on the driving mechanisms.
In the first part of the talk, we will describe recent efforts to combine synchrotron-based measurements of an evolving MSFC with high-fidelity computational reconstructions and machine learning to elucidate the microstructural and micromechanical features that govern local rate of MSFC propagation. Ex-situ (post mortem) techniques were employed to characterize fatigue-crack propagation within the microstructure of an aluminum alloy. The experimental characterization involved X-ray tomography along with near-field high-energy X-ray diffraction microscopy, which provided a 3D grain map adjacent to fatigue-crack surfaces. The experimental data were then used to digitally reconstruct the measured polycrystalline volume as a way to reproduce, within a computational environment, the heterogeneous micromechanical fields in local neighborhoods along the observed crack fronts.
The second part of the talk will describe a parallel effort to develop a voxel-based meshing framework to simulate the evolution of arbitrarily-shaped discontinuities throughout polycrystalline volumes. The framework allows for explicit representation of crack surfaces and grain boundaries. The meshing framework relies on a voxel-based description of the microstructure of interest, which is iteratively updated to allow for an explicit discontinuity to interact with grain-boundary interfaces by propagating through, near, or along grain boundaries. The framework also allows for multiple discontinuities to coalesce with one another. The new meshing framework, in combination with improved rules for predicting 3D crack-shape evolution, will serve to improve predictive capabilities for MSFC evolution and ultimately for fatigue life of structural components.
10:30 AM - *PM03.08.05
Grain Boundary and Interface Design in Nanostructured Films for Fracture Toughness Enhancement—A Micromechanical Study
Rostislav Daniel 1 , Christian Mitterer 2 , Jozef Keckes 3
1 Christian Doppler Laboratory for Advanced Synthesis of Novel Multifunctional Coatings at the Department of Physical Metallurgy and Materials Testing, Montanuniversität Leoben, Leoben Austria, 2 Department of Physical Metallurgy and Materials Testing, Montanuniversität Leoben, Leoben Austria, 3 Department of Materials Physics, Montanuniversität Leoben and Erich Schmid Institute for Materials Science, Austrian Academy of Sciences, Leoben Austria
Show AbstractAn enhancement of fracture toughness of hard nanostructured materials without compromising the strength is very challenging as the ability of most hard materials to deform inelastically is rather limited. This is given by the activation of dislocation glide on most slip systems in hard nanocrystalline ceramic materials requiring much higher stress than that for brittle fracture along grain boundaries. Though, grain boundaries with weak cohesive energy may be used as a toughening element of brittle nanostructured materials if they are specifically structured and oriented with respect to the expected crack path. In this paper, various innovative design strategies for fracture toughness enhancement of brittle ceramic nanostructured materials will be presented, which rely, on the one hand, on a variation in material microstructure and mechanical property depth-distributions and, on the other hand, on dedicated grain-boundary and interface design. Both these approaches allow for an effective fracture toughness enhancement of hard yet brittle nanostructured materials by multiple crack deflection at weak interfaces or at tilted grain boundaries. In this way, even common nanocrystalline brittle materials such as TiN may exhibit considerably enhanced plasticity and fracture toughness achieving values more than 150% of their monolithic counterparts with columnar microstructure. The results demonstrate that a dedicated design of grain boundaries offers great potential for the development of novel hard fracture resistant materials.
11:00 AM - PM03.08.06
Cohesive Stress Heterogeneities and the Transition from Intrinsic Ductility to Brittleness
Döme Tanguy 1
1 , Institut Lumière Matière, Université Lyon 1, Villeurbanne France
Show AbstractThe influence of nanoscale cavities on the fracture of a grain boundary is studied by atomistic simulations. The crack crystallography is chosen such that dislocation emission is easy. Metropolis Monte Carlo simulations are used to create realistic nanoscale cavities along the Σ33{554}[110] symmetrical tilt grain boundary. Increasing the grain boundary coverage leads to a transition from a ductile behavior of the tip to a brittle one, in good agreement with the recent experiments by Miura et al. (Journal Of Nuclear Materials 457 (2015) p. 279). Even at the highest coverage, the character of the crack is highly sensitive to the initial position of the tip with respect to the smallest cavities. The transition is not sharp. This complexity cannot be accounted for by the Rice and Thomson criterion based on the comparison between the critical stress intensity factors for dislocation emission, at the tip (kIe), and brittle crack propagation (kIc). Indeed, even if there is a drop of the work of separation with the amount of damage in the structure is found, kIc is still in the upper range of the kIe values. Instead of this criterion, it is shown that a cohesive zone model, with parameters extracted from the simulations and enriched with a criterion for plasticity, can describe the transition. It emphasizes the role of cohesive stress heterogeneities along the interface and rationalizes the complexity found in the simulations. A parametric study determined the characteristics of the heterogeneity which constitutes an obstacle to brittle crack propagation. These could be guidelines to designing interfaces more resistant to solute embrittlement, in general.
11:15 AM - PM03.08.07
Hard Amorphous Shell on Core-Shell Nanowire for Governing Dislocation Nucleation—Local versus Homogeneous Plasticity
Julien Godet 1 , Maxime Guillotte 1 , Clarisse Furgeaud 1 , Laurent Pizzagalli 1 , Michael Demkowicz 2
1 Pprime Institut, CNRS, University of Poitiers, Poitiers France, 2 Materials Science and Engineering, Texas A&M University, College station, Texas, United States
Show Abstract
In order to evaluate the role of a hard amorphous silicon (a-Si) shell on the deformation of a soft crystalline gold core, we have investigated the mechanical properties of the Au@a-Si core-shell nanowire (NW) by molecular dynamics simulations. We have first optimized an existing parametrization of the MEAM potential to better reproduce the mechanical properties of gold and silicon as well as the Au-Si interactions. The comparison of the tensile tests performed on pristine Au NW, empty amorphous-Si shell and Au@a-Si core-shell NW reveals that the hard amorphous shell works against the growth of ledges left by localized plasticity. In consequence, the localized plasticity and the expansion of nano-twin are reduced. The confinement of the dislocations in the core due to the hard shell do not lead to an apparent hardening of the nanostructure. But a homogeneous plastic deformation of the core-shell nanowire is observed at almost a constant flow stress equal to the yield stress. This behavior is characteristic of an elastic-perfect plastic mechanical regime.
11:30 AM - *PM03.08.08
Phase Transformation in Superelastic NiTi Alloys During Uniaxial, Multiaxial and Strain Path Change Loading Conditions—In Situ Synchrotron and SEM-DIC Experiments
Helena Van Swygenhoven-Moens 1 , Wei-Neng Hsu 1 , Efthymios Polatidis 2 , Miroslav Smid 2 , Steven Van Petegem 2
1 , Ecole Polytechnique Federale de Lausanne & Paul Scherrer Institute, Switzerland, Villigen Switzerland, 2 , Paul Scherrer Institut, Villigen Switzerland
Show AbstractThe superelastic behavior of NiTi alloys has been studied mainly during uniaxial tension/compression experiments. It is well known that during the forward and backward phase transformation, the moving interfaces between the parent and martensite phases leave behind them some remaining damage (seen as residual strain). This occurs by the imperfect phase-transformation reversibility that results in some retained martensite and in some of the geometrically necessary dislocations to be retained. During operational conditions of stents, some parts of the NiTi alloy component will however undergo complex biaxial stress states and/or experience strain path changes which can lead to a faster degradation of the superelastic properties upon repeated deformation cycles due to the development of dislocation networks and/or remaining martensitic regions creating sub-grain interfaces.
Recently, a novel miniaturized biaxial tensile machine using cruciform shaped samples [1] was developed allowing to apply in-plane biaxial stress states with arbitrary stress ratios and to perform strain path changes on thin-sheet metals. The device can be operated (i) inside a scanning electron microscope (SEM) where combined with High Resolution Digital Image Correlation (HR-DIC) displacements can be followed insitu and mapped with a sub-micron resolution, and (ii) in situ during Laue or powder synchrotron diffraction experiments following the evolution of lattice strains, peak broadening, phase transformations etc.
In the present study we report on in situ experiments performed using cruciform-shaped samples of commercial superelastic polycrystalline NiTi alloys. The microstructure of the material consists of large micron-sized grains containing bands of a nanosized mosaic structure. At the MS beamline of the Swiss Light Source, in situ synchrotron powder diffraction experiments were performed, yielding quantitative information on the martensitic phase transformation and lattice strain evolution during complex loading conditions and changes in strain path. This study is complemented by conventional DIC and in situ HR-DIC experiments inside an SEM to track the localization of the strain associated with the phase transformation. Combined with EBSD and ECCI, the remaining martensitic/austenitic interfaces and dislocation structures after cycling under uniaxial and multiaxial loading conditions are compared.
This research is performed within the ERC Advanced Grant MULTIAX (339245).
[1] S. Van Petegem, A. Guitton, M. Dupraz, A. Bollhalder, K. Sofinowski, M.V. Upadhyay, H. Van Swygenhoven, Experimental Mechanics (2017) 57 p. 569.
PM03.09/EM05.12: Joint Session II: Interfaces in Oxides
Session Chairs
Tor Grande
David Rowenhorst
Wednesday PM, November 29, 2017
Sheraton, 3rd Floor, Commonwealth
1:30 PM - PM03.09.01/EM05.12.01
Metal Diffusion along the Metal-Ceramic Interface in Partially Dewetted Thin Films
Hagit Barda 4 , Dor Amram 2 , Eugen Rabkin 1
4 , Technion–Israel Institute of Technology, Haifa Israel, 2 , Massachusetts Institute of Technology, Boston, Massachusetts, United States, 1 , Technion, Haifa Israel
Show AbstractThe established hierarchy of diffusion paths in crystalline solids, in the order of increasing diffusivities, is bulk diffusion, dislocation core diffusion, grain boundary diffusion, and surface diffusion. The position of diffusion along the interfaces between dissimilar materials in this hierarchy is largely unknown. In this work, we aimed at filling this gap by studying the metal hetero-diffusion along the metal-ceramic interface.
In a recent work [1], an indirect evidence for fast self-diffusion of Ni along the Ni-sapphire interface has been obtained. Based on these results, we propose a new method of measuring the metal heterodiffusion along the Ni-sapphire interface. We prepared a series of samples, starting from a partially dewetted 40 nm-thick Ni film, which consists of holes surrounded by a bi-crystalline film, and covered by a 4 nm thick Au deposited film. Afterwards, a diffusion annealing was performed at the temperature range of 450°C - 600°C, at which the morphology of the Ni film is highly stable. Gold atoms diffused from the edge of the holes along the Ni-sapphire interface, and the concentration decay in the direction from the hole edge to the unperturbed film was quantitatively characterized by high resolution transmission electron microscopy. Based on the suggested method, diffusion coefficient of Au along a film-substrate interface was determined.
[1] D. Amram, L. Klinger, N. Gazit, H. Gluska, E. Rabkin. ”Grain boundary grooving in thin films
revisited: the role of interface diffusion”, Acta mater. 2014; 69:386.
1:45 PM - PM03.09.02/EM05.12.02
Computational Investigations on the Interface Properties to Improve the Stability of Ag Thin Film on Oxide Substrates in Low-Emissivity Glasses
Mingfei Zhang 1 , Liang Qi 1
1 , Univ of Michigan, Ann Arbor, Michigan, United States
Show AbstractTo improve the energy efficiency of windows and buildings, a multilayer thin-film of various metal oxides and a low-emissivity material (such as silver) are often deposited on the architectural glass. However, the interfaces between the Ag thin film (thickness ~ 10 nm ) and its adjacent oxides, usually ZnO or Al-doped ZnO, have relatively weak interfacial bonding strength and often result in dewetting and agglomeration of Ag thin film on the oxide substrate during the thin film processing procedures and the long-time service. Furthermore, hydrogen and other impurities can penetrate the multilayer and intensify the above detrimental effects when the glass is exposed to the external environment. We plan to solve this problem from two aspects by computational modelling. First, first-principles calculations will be applied to explore the possible chemical doping into the oxide substrates to enhance the bonding strength between Ag thin film and the substrates under the co-existence of interfacial impurities. Second, since the agglomeration of Ag thin film usually starts from the grain boundary grooving in the Ag polycrystalline thin film, atomistic simulations and numerical models will be performed to investigate the kinetics of grain boundary grooving in Ag nano thin film and explore the possible strategies to impede the grooving kinetics. The results will provide physical insights on the design of multilayer thin-film processing procedures to improve Ag thin film wettability and stability on oxide substrate to produce low-emissivity glasses with enhanced and enduring performance.
2:00 PM - PM03.09.03/EM05.12.03
Atomistic Simulation of Interface-Driven Self-Alignment of Si-SiO2 Nanostructures
Thomas Pruefer 1 , Karl-Heinz Heinig 1 , W. Moeller 1
1 , Helmholtz Zentrum Dresden Rossendorf, Dresden Germany
Show AbstractSi nanostructures are very promising candidates for optical and electrical applications. Charged nanocluster can be used for data storage [2]; their discrete energy levels can be used for logic operations; sponge nanostructures can be used as the ion conductor in fuel cells. The size-dependency of their energy levels makes them interesting for application in colour displays.
Among a lot of other methods to synthesize nanoclusters or sponges we present an approach which allows a self-alignment of nanostructures at an interface. The basic idea is to bring together Si, SiO2 and SiOx and anneal it to cause phase separation of SiOx. The interfaces between Si/SiOx and SiOx/SiO2 act as driving forces for the self-alignment of the separated Si and SiO2. To create SiOx we consider 2 processes: (i) Deposition of SiOx films by PVD or CVD and (ii) Ion beam Mixing of Si/SiO2 interfaces.
By PVD it’s possible to create arbitrary shapes of Si/SiO2/SiOx layerstacks. The subsequent annealing causes different effects at the interface. Mainly depending on the structure of the layerstack, but also on the annealing time, different reaction pathways can be observed. The system can end up with different numbers of cluster layers or sponge structures, aligned parallel to the interface. Here we show how and why it is possible to control the sizes, densities and distances of these structures.
The ion irradiation through a Si/SiO2 interface causes mixing of both phases and transforms the interface into SiOx. This method is not that flexible as PVD, but it’s easier to be implemented into common industrial technologies, like the production of CMOS compatible devices. The reformation of the Si/SiO2 interface during heat treatment is again acting as a driving force for the self-alignment and forms a zone between the interface and the resulting nanostructures which is denuded of excess Si. In this case, sizes and density can be controlled by irradiation and annealing parameters.
Earlier studies [1] have proven the reliability of dot formations using ion beam mixing technologies for application as memories [2]. Here, we show simulation results for the formation of Si nanostructures at interfaces in layerstacks of Si, SiOx, SiO2 and basic principles of the driving forces for this kind of self-alignment. Computer simulations using the binary collision approximation (TRIDYN [3]) and the kinetic monte carlo method [4] are employed to subsequently describe the ion irradiation and annealing processes, respectively.
This part of the work is being funded by the European Union’s Horizon 2020 research and innovation program under Grant Agreement No 688072 (Project IONS4SET).
[1] T. Müller et al., Appl. Phys. Lett. 81 (2002) 3049; ibid. 85 (2004) 2373.
[2] K.H. Heinig et al., Appl. Phys. A77 (2003)17.
[3] W. Möller, W. Eckstein, Nucl. Instr. and Meth. in Phys. Res. B2 (1984) 814
[4] M. Strobel et al., Phys. Rev. B64 (2001)245422.
2:15 PM - PM03.09.04/EM05.12.04
Phase Field Modeling of Grain Boundary Evolution in Porous Oxides—Grain Growth and Pore Mobility Effects
Anter El-Azab 1 , Karim Ahmed 2
1 , Purdue University, West Lafayette, Indiana, United States, 2 , Idaho National Laboratory, Idaho Falls, Idaho, United States
Show AbstractWe present a phase field model for investigating grain boundary evolution in porous oxides with applications to UO2 and CeO2. The model takes into account the interactions between pores and grain boundaries as well as the pore mobility effects. Using a formal asymptotic analysis, the phase field model was matched to its sharp-interface counterpart and all model parameters were uniquely determined. Therefore, the model is able to obtain accurate growth rates that can be compared with experiments. The model was used to reveal various growth regimes in porous oxides and sort the boundary-controlled versus pore-controlled growth kinetic regimes. The model results showed that the pore breakaway phenomenon can only be observed in 3D simulations. The important features of the model and results will be presented.
2:30 PM - PM03.09/EM05.12
BREAK
3:30 PM - *PM03.09.05/EM05.12.05
Probing the Electrical Potential Distribution at SrTiO3 Hetero-Interfaces through Transient Transport Measurements
Roger De Souza 1
1 Institute of Physical Chemistry, RWTH Aachen University, Aachen Germany
Show AbstractThe combination of 18O/16O exchange and Secondary Ion Mass Spectrometry (SIMS) analysis constitutes a powerful tool for probing the behaviour of oxygen vacancies in oxides. In this contribution, I demonstrate the application of this method to investigating the behaviour of oxygen vacancies in SrTiO3 and at its hetero-interfaces. The diffusion kinetics in single-crystal SrTiO3 from 50 < θ / °C < 1400 will be presented. Non-uniform equilibrium distributions of oxygen vacancies at three hetero-interfaces will be discussed: the O2(g)|SrTiO3 interface, the SrRuO3|SrTiO3 interface and the LaAlO3|SrTiO3 interface. The variation of the electrostatic potential across such interfaces will be extracted and compared with complementary measurements.
4:00 PM - *PM03.09.06/EM05.12.06
The Electrochemical Interface—Progress toward a Unified Continuum Theory for Dilute and Concentrated Systems
David Mebane 1
1 , West Virginia Univ, Morgantown, West Virginia, United States
Show AbstractInterfaces, surfaces and other extended defects often control the properties of ion conducting materials. Interfacial properties are often governed by charge separation. The dominant continuum models for space charge phenomena are decades old and are strictly valid only in the dilute limit; atomistic models are constrained by the inherent multi-scale nature of space charge, wherein a surface is in equilibrium with a macroscopically distant bulk phase. The development of quantitative models for observed phenomena such as co-accumulation of oppositely charged defects in concentrated systems thus relies on the emergence of a continuum theory (or a combination of atomistic and continuum approaches) for space charge in the concentrated case. This talk will detail the development over the past couple of years of the Poisson-Cahn space charge theory, including its success in replicating experiment in both dilute and concentrated systems, and ongoing efforts to define and validate a standard theoretical formalism.
4:30 PM - PM03.09.07/EM05.12.07
Differences in Space-Charge Formation at Grain Boundaries in BaZrO3 and BaCeO3
Anders Lindman 1 , Edit Helgee 1 , Goran Wahnstrom 1
1 , Chalmers University of Technology, Gothenburg Sweden
Show AbstractProton conducting ceramics as electrolytes in solid oxide electrochemical devices are a promising alternative for reducing the operating temperature to the intermediate regime (400-700 °C). Among the best proton conductors are acceptor-doped BaZrO3 and BaCeO3, which both exhibit considerable bulk proton conductivity in humid atmospheres, and a lot of attention has been devoted towards BaZrO3-BaCeO3 solid solutions such as BaZr0.7Ce0.2Y0.1O3-d. In these polycrystalline materials, however, grain boundaries (GBs) display high proton resistivity, which severely limits the overall proton transport. This has been attributed to the presence of space-charges at the GBs that cause a depletion of protonic carriers. This effect is less prominent in BaCeO3, but in contrast to BaZrO3, BaCeO3 has problems with chemical stability as it reacts with CO2. The more resistive nature of GBs in BaZrO3 compared with BaCeO3 is evident in the activation energy for the proton GB conductivity (cf. 0.99 eV with 0.79 eV), while the bulk conductivities are similar (cf. 0.46 eV and 0.45 eV).
We have performed a density-functional theory based computational study in order to elucidate the origin to the differences in space-charge formation at GBs in BaZrO3 and BaCeO3, caused by segregation of charged oxygen vacancies and protons. We consider formation of these defects both in bulk and at GBs, for which a proper comparison of the two materials requires both aligned electronic structures and appropriate GB configurations. For the latter, it is essential that we compare GBs in BaZrO3 and BaCeO3 that are as structurally similar as possible and to this end we have selected four symmetric tilt GBs in BaCeO3 that are analogous to the (111)[-110] and (112)[-110] GBs in BaZrO3.
We find that the oxygen vacancy formation and segregation energy is quite similar in BaZrO3 and BaCeO3. For protons, on the other hand, the segregation energy is systematically more negative in BaZrO3 by about 0.3 to 0.5 eV. This difference is found not to be related to the GBs, where protons have similar formation energies in the two materials, but to the bulk phases where protons are less stable in the cubic environment of BaZrO3. The reason for this is found to be related to hydrogen bond formation, which is facilitated in the distorted lattice structures of the GBs and the orthorhombic bulk phase of BaCeO3. Segregation energies are evaluated in a thermodynamic space-charge model, which yields space-charge potentials that are 0.2-0.3 V lower in BaCeO3 compared with BaZrO3. We conclude that proton segregation is consistently more favourable in BaZrO3 compared with BaCeO3 due to differences in proton stability in the bulk phases, and this may be the reason for the less severe GB effect in BaCeO3.
4:45 PM - PM03.09.08/EM05.12.08
Interfacial La Vacancies Ordering and Stress Relaxation Mechanism of LaMnO3 /DyScO3 System
Alexander Kvit 1 , Jie Feng 1 , Chenyu Zhang 1 , Dane Morgan 1 , Paul Voyles 1
1 , University of Wisconsin-Madison, Madison, Wisconsin, United States
Show AbstractWe report detailed structural analysis of thin LaMnO3 (LMO) films grown on DyScO3 (DSO) substrate. The DSO substrate has nearly perfect epitaxial matching with LMO film, but the difference in coefficients of thermal expansion between LMO and DSO and the onset of the Jahn-Teller distortion in LMO below the growth temperature leads to a quite complex stress relaxation at the interface. The LMO film consists of alternating domains rotated by 90° with respect to each other and the substrate. We observe no interface misfit dislocations. We utilize high precision quantitative STEM imaging with superior signal to noise ratio via non-rigid registration and averaging of a series of STEM images. High-angle annular dark field (HAADF) images obtained by this method reveal periodic changes of the La column intensity at LMO/DSO interface. These images are consistent with ordered La vacancies at the LMO/DSO interface. Atomic-scale chemical imaging of composition and bonding of LMO/DSO interface by electron energy loss spectroscopy (EELS) mapping excludes the possibility of antisite defects formation or residual impurity accumulation at the interface. Using the sub-picometer precision in locating atomic column positions from the high precision STEM images, we can map atomic column shifts near the interface and the stress relaxation inside individual domains in real space. The effect of La vacancy ordering on LMO/DSO interface and individual La vacancies in LMO film on residual strain relaxation will be discussed.
Symposium Organizers
Ying Chen, Rensselaer Polytechnic Institute
Erik Bitzek, University of Erlangen-Nuremberg
Maria Teresa Perez Prado, IMDEA Materials Institute
David Rowenhorst, U.S. Naval Research Laboratory
PM03.10: Grain Boundary Segregation and Nanocrystalline Configuration
Session Chairs
Srikanth Patala
David Rowenhorst
Thursday AM, November 30, 2017
Hynes, Level 2, Room 209
8:15 AM - *PM03.10.01
Interfaces and Defect Composition at the Near-Atomic Scale
Baptiste Gault 1
1 , Max-Planck-Institut für Eisenforschung GmbH, Düsseldorf Germany
Show AbstractUnderstanding the minutiae of the composition and structure of interfaces in materials is crucial to establish relationships with their properties. Modern techniques, such as atom probe tomography, are now able to provide insights into the local composition of interfaces with a high degree of accuracy. In this presentation, I will review the application of APT, often directly correlated with electron microscopy, to reveal the fine structure of grain boundaries and interfaces in a range of metallic alloys, including Al, Fe and Ni-based. Results from these investigations are discussed in relation to the resulting properties of the systems under scrutiny.
8:45 AM - *PM03.10.02
Recent Advances and Open Problems in Interfacial Segregation
Pavel Lejcek 1 , Mojmir Sob 2 3 4
1 , Institute of Physics, Academy of Sciences of the Czech Republic, Praha Czechia, 2 , Central European Institute of Technology, CEITEC MU, Masaryk University, Brno Czechia, 3 , Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Brno Czechia, 4 Department of Chemistry, Faculty of Sciences, Masaryk University, Brno Czechia
Show AbstractSolute segregation at grain boundaries and free surfaces as well as their effect on intergranular cohesion have been intensively studied in the past decades. As a consequence, there are numerous theoretical results as well as experimental data on corresponding characteristic energies and/or enthalpies enabling wide-ranging comparisons and significant generalizations. Recently, significant advances in interfacial segregation were achieved by determining segregation energies of numerous solutes in a number of technologically important materials, introducing segregation volume to describe the pressure effect on grain boundary segregation, and experimental as well as theoretical determination of magnetic moments at the grain boundaries. Nevertheless, some important questions remain still unsolved, for example:
- How can be the experimental results on the grain boundary segregation compared reliably to their theoretical counterparts? Namely, segregation energies for solutes with high solid solubility in the matrix are well comparable with the calculated values whereas those for solutes with low solid solubility exhibit enormous scatter, both in measurement and in calculations.
- Is the segregation site of a solute in the grain boundary core substitutional or interstitial? The answer of this question is mainly important for basic understanding of the grain boundary segregation but also e.g. for calculations the strengthening/embrittling energies which characterize the role of the solute in changing the cohesion energy of the host.
These and other questions will be discussed in detail in the present contribution. We will also show that entropy of grain boundary segregation is a very important quantity which cannot be neglected in thermodynamic considerations as it plays a crucial role in prediction of grain boundary segregation, in classification of grain boundaries and in the preference of the segregation site at the boundary.
9:15 AM - PM03.10.03
Atomistic and Mesoscale Modeling of Grain Boundary Segregation – Part I
Blas Uberuaga 1 , Enrique Martinez 1 , Wolfgang Windl 2 , Logan Ward 2 , Fadi Abdeljawad 3
1 , Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 2 , The Ohio State University, Columbus, Ohio, United States, 3 , Sandia National Laboratories, Albuquerque, New Mexico, United States
Show AbstractUnderstanding the segregation of elements in alloyed nanocrystalline metals is important for understanding, predicting, and designing materials for applications in a range of fields from structural materials to nuclear energy systems. However, how the combined factors of the atomic structure of the interfaces and the nature of the alloying elements impact this segregation are still open questions. A set of interatomic interactions for alloying elements in Ni has recently been derived, describing the behavior of a range of FCC, BCC, and HCP elements in Ni. We use these potentials to examine elemental segregation to a set of grain boundaries with varied grain boundary character. Under the assumption that all of these elements are substitutional, we use molecular statics and limited Monte Carlo simulations to examine two regimes of segregation: that of an isolated solute and a concentrated regime in which the equivalent of multiple monolayers of solute are placed at the grain boundary. We find that both the nature of the grain boundary and the nature of the solute impact the segregation behavior, with some solutes essentially wetting the boundaries with other solutes forming more three-dimensional precipitates at the boundaries. We analyze the behavior in terms of fundamental interactions, such as the free volume at the boundary and the solute-solute interaction in the bulk. These results provide important insight and data for mesoscale models that will be described in Part II of this work.
9:30 AM - PM03.10.04
Atomistic and Mesoscale Modeling of Grain Boundary Segregation – Part II
Fadi Abdeljawad 1 , Stephen Foiles 1 , Blas Uberuaga 2 , Enrique Martinez 2
1 , Sandia National Laboratories, Albuquerque, New Mexico, United States, 2 , Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show AbstractNanocrystalline metals (NCs) exhibit a unique combination of properties that render them an attractive material of choice for many applications. Owing to the large area density of grain boundaries (GBs) in NCs, these systems are unstable against grain growth and other homogenization processes even at low service temperatures. In recent years, GB solute segregation has been proposed as a route to thermally stabilize the grain structure of NCs. Based on a diffuse interface model that accounts for both bulk and GB thermodynamics, solute-GB interactions, and GB migration, we present quantitative analysis of GB segregation and its impact on grain growth dynamics. Analytical treatments and simulation results identify regimes where the reduction in GB energy can be large. Next, GB anisotropy is incorporated in the modeling framework, where the segregation energy is allowed to depend on the GB character (GB geometric degrees of freedom). As a demonstration of the modeling capability, segregation energies are parameterized based on results from atomistic simulations of a wide range of GB types in Ni-based binary alloys. Mesoscale simulation results utilizing such atomistic data highlight the role of GB segregation anisotropy on the solute distribution, grain growth dynamics and overall thermal stability of NCs. On the whole, this modeling framework provides an avenue to explore the role of GB anisotropy on the microstructural evolution, solute transport and thermal stability of NCs.
This work is supported by the Laboratory Directed Research and Development program at Sandia National Laboratories, a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.
9:45 AM - PM03.10.05
Effects of Grain Boundary Segregation on Alloy Thermodynamics in Nanocrystalline Materials
Arvind Kalidindi 1 , Christopher Schuh 1
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractThe large volume fraction of grain boundaries that provides improvements in yield strength and certain functional properties in nanocrystalline materials also affects the equilibrium alloy configuration, where solute can preferentially occupy grain boundary sites. Grain boundary segregation presents a form of ordering that can play a significant role in nanocrystalline materials and thus needs to be accounted for in the alloy configuration space from a thermodynamic perspective. Using Monte Carlo simulations, we explore the interplay between grain boundary segregation and second phase formation in fine-grained alloys. By determining the equilibrium configurations and their free energies with varying enthalpies of grain boundary segregation, we study how the presence of grain boundaries can influence the enthalpic and entropic landscape in nanocrystalline alloys, particularly focusing on effects regarding phase transitions and the thermal stability of nanometer-scale grain sizes.
10:30 AM - *PM03.10.06
Strategies to Control Microstructure and Properties of Nanocrystalline Materials
Martin Harmer 1 , Christopher Marvel 1 , B. Hornbuckle 2 , Kristopher Darling 2
1 , Lehigh University, Bethlehem, Pennsylvania, United States, 2 , U.S. Army Research Laboratory, Aberdeen, Maryland, United States
Show AbstractThe stability and performance of nanocrystalline materials strongly depend on grain boundaries. Because of the fine length scales associated with grain boundaries, there are many practical challenges that must be overcome to fully leverage nanocrystalline materials for new applications; namely, scaling nanostructured powders to bulk components, experimentally characterizing nanocrystalline grain boundaries on the atomic scale, and de-convoluting thermal stability mechanisms. This talk will review alternative strategies, through the utilization of grain boundary complexions, to maximize stability and mechanical properties of nanocrystalline ceramics and metals. First, the concept of complexion time-temperature-transformation diagrams will be presented as an alternative mechanism for two-step sintering. Distinct complexion transitions have been identified in doped-Y2O3 and doped-Al2O3, and processing routes are suggested to avoid high mobility grain boundary complexions. Furthermore, complexion stabilized nanoscale particles in Ni-W and Cu-Ta metallic alloys will be presented. These particles simultaneously stabilize the microstructures and enhance hardness and creep resistance.
11:00 AM - *PM03.10.07
Nanostructure Configurations in Ternary Alloys
Wenting Xing 1 , Arvind Kalidindi 1 , Sebastian Kube 2 , Dor Amram 1 , Jan Schroers 2 , Christopher Schuh 1
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 , Yale University, New Haven, Connecticut, United States
Show AbstractThe stability of nanostructured systems that exhibit grain boundary segregation has been widely studied in binary alloys. Because there is only one solute element in a binary alloy, the range of possible stable nanostructures is limited, with only a handful of morphologically distinct states. In ternary nanocrystalline alloys, on the other hand, many new configurational possibilities can be accessed since the two solute elements can have additional interactions that lead to nontrivial morphologies. Here we lay the groundwork for the computational exploration of this phase space using lattice Monte Carlo simulations, and the experimental exploration of it by combinatorial methods. We exercise this ternary framework in Pt-based nanocrystalline alloys with thermodynamic preferences for both grain boundary segregation and second-phase precipitation.
11:30 AM - PM03.10.08
Thermodynamic Modelling of Precipitate Stabilization through Interface Solute Segregation
Srikanth Patala 1 , Sourabh Kadambi 1
1 , North Carolina State University, Raleigh, North Carolina, United States
Show AbstractA widely used strategy to strengthen alloys is through precipitation of intermetallics from solid-solution. At high temperatures, however, their performance degrades as precipitates coarsen to reduce the overall interfacial energy. In certain multi-component alloys, it has been shown that solute segregation to these interfaces could reduce the interfacial energy and thus the driving force for coarsening. In this talk, I will present a thermodynamic model that describes the Gibbs free-energy of such precipitating systems as a function of region-specific concentrations, volume fractions, and chemical interaction parameters. Results for Mg-Sn-Zn, for favorable interactions of Zn at the interface, show that: (i) Zn segregates to the interface to reduce the interfacial and system energy; and (ii) nano-sized Mg2 Sn precipitates are stabilized through interface Zn segregation. With further extension to include elastic stain energy effects, the model is expected to provide a realistic prediction of segregation and precipitate stabilization and enable identification of such systems.
11:45 AM - PM03.10.09
Grain Boundary Segregation Strengthening in Nanocrystalline Alloys
Jason Trelewicz 1
1 , Stony Brook University, Stony Brook, New York, United States
Show AbstractStable nanocrystalline phases employing solute enriched grain boundaries are being realized in a myriad of alloy systems and driving extraordinary advances in the design, processing, and technological applications of bulk nanocrystalline materials. However, augmenting the grain boundary chemical and structural state for stabilization purposes can also have marked impacts on the mechanical behavior. In this presentation, a new strengthening mechanism is explored in solute-stabilized nanocrystalline alloys – grain boundary segregation strengthening – with a focus on the underlying mechanisms and their dependence on fundamental grain boundary properties. Stable nanocrystalline configurations are first identified through lattice Monte Carlo modeling in binary aluminum alloys, selected due to their technological importance as high specific strength metals. Based on these predictions, we select nanocrystalline Al-Mg for synthesis via mechanical milling and tailor the grain boundary segregation state through annealing. The effect of grain boundary doping on hardness and strength is isolated in these materials and discussed in the context of the interfacial solute excess and grain boundary energies from the predicted equilibrium alloy configurations. Molecular dynamics simulations are finally performed to connect strengthening trends and their scaling with grain boundary properties to the underlying deformation mechanisms. We find that grain boundary plasticity is suppressed by solute enrichment reducing the grain boundary energy, which in turn delays the onset of dislocation plasticity. Strengthening due to grain boundary segregation is thus attributed to more stable interface configurations inhibiting grain boundary mediated plasticity, establishing a new strengthening mechanism that can be exploited in the design of solute-stabilized nanocrystalline alloys.
PM03.11: Interfaces in Multilayers and Nanocomposites
Session Chairs
Erik Bitzek
Megumi Kawasaki
Thursday PM, November 30, 2017
Hynes, Level 2, Room 209
1:30 PM - *PM03.11.01
Microstructures and Deformation Behavior of Metallic Nanolayered Composites under Cyclic Loading Conditions
Ruth Schwaiger 1
1 , Karlsruhe Institute of Technology, Eggenstein-Leopoldsh Germany
Show AbstractMetallic nanolayered composites have demonstrated a range of superior mechanical properties, including high strength and high strain to failure as well as improved wear resistance and fatigue behavior. Previous investigations have shown that deformation and strength of multilayers depend on the layer thickness and the type of interface between the layers, which directly controls the barrier strength of the interface and the stability of the layered structure under mechanical loading. In this presentation, we will present our recent efforts to understand the role of the interface in deformation and failure under cyclic loads. Different materials combinations were studied by cantilever beam bending, microcompression, and nanoindentation. The microstructures were investigated by scanning and transmission electron microscopy with the goal to link the evolution of the nanolayered structures and interface properties. Interface effects on the cyclic deformation behaviors of nanolayered composites will be discussed.
2:00 PM - PM03.11.02
Deformation Mechanism Map of Cu/Nb Nanoscale Metallic Multilayers as a Function of Temperature and Layer Thickness
Jon Molina-Aldareguia 1 , Jeromy Snel 1 , Miguel Monclus 1 , Nathan Mara 2 , Irene Beyerlein 3 , Javier Llorca 1
1 , IMDEA Materials Institute, Getafe Spain, 2 , Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 3 , University of California, Santa Barbara, California, United States
Show AbstractThe mechanical properties and deformation mechanisms of Cu/Nb nanoscale metallic multilayers (NMMs) manufactured by accumulative roll bonding (ARB) are studied at 25 °C and 400 °C. Cu/Nb NMMs with individual layer thicknesses between 7 and 63 nm were tested by in-situ micropillar compression inside a scanning electron microscope. Yield strength, strain-rate sensitivities and activation volumes were obtained from the pillar compression tests. The deformed micropillars were examined under scanning and transmission electron microscopy in order to examine the deformation mechanisms active for different layer thicknesses and temperatures. The analysis suggests that room temperature deformation was determined by dislocation glide at larger layer thicknesses and dislocation transmission at interfaces at the thinner layer thicknesses. The high temperature compression tests, in contrast, revealed superior thermo-mechanical stability and strength retention for the NMMs with larger layer thicknesses with deformation controlled by dislocation glide. A remarkable transition in deformation mechanism occurred as the layer thickness decreased, to a deformation response controlled by dislocation climb interfaces, which resulted in temperature-induced softening. A deformation mechanism map, in terms of layer thickness and temperature, is proposed from the results obtained in this investigation.
2:15 PM - PM03.11.03
Fractography, Microstructure and Thermal Stability of Multilayer CNx/TiN Composite Films Prepared by DC Reactive Magnetron Sputtering
Gongsheng Song 1 , Guodong Zhang 1 , Chunxu Pan 1
1 , Wuhan University, Wuhan China
Show Abstractβ-C3N4 has been considered as a hypothetical super-hard materials. However, the full crystalline carbon nitride film is not easy to be prepared because of its instability, and in most case, it is in the form of amorphous carbon nitride (α-CNx) with x typically on the order of 0.3-0.4 and the hardness is of only 20-30Gpa. it has been recognized that when a TiN is used as a structure template, the full crystalline CNx/TiN nanocomposite films can be prepared with high hardness over 45 Gpa. The adhesion strength, fracture toughness and failure mechanism of the CNx/TiN film were mostly concerned due to its applications in microelectronics, wear resistant coatings, etc.
In this paper, a multilayer CNx/TiN composite film on high-speed steel substrate was prepared by using a multi-arc assisted dc reactive magnetron sputtering system. The cross-section observation reveals that the multilayer CNx/TiN composite films showed a pure cleavage fracture due to its super-high hardness, and the interfacial strength between the film and substrate is associates with the film thickness. It was found that there exist a critical thickness (2μm) for the deposited multilayer CNx/TiN composite films, that is to say, when the film is thicker than 2μm, a disbonding will appear along the interface due to the large stress concentration. The industrial applications in cutting tools showed that this composite film prolonged the cutting life of drills for almost 10 times.
In addition, thermal stability for the CNx/TiN composite films is of fundamental importance for its applications. Our experimental results indicated that the films transformation temperature was at 400°C during annealing, i.e., below 400°C the microstructures and mechanical properties including hardness and adherence force of the composite films kept stable, while above 400°C they were declined rapidly. The reason was that the CNx layer started to decompose at 400°C and carbon diffused onto surface across the TiN layer, which led to the decrease in mechanical properties. However, corrosion resistance of the degraded film in acid solution increased with annealing temperatures, due to amorphous carbon formation on surface the corrosion resistance.
2:30 PM - PM03.11.04
Shock Response of Cu/Ta Multilayer Systems at the Atomic Scales
Jie Chen 1 , Avinash Dongare 1
1 , University of Connecticut, Storrs, Connecticut, United States
Show AbstractMetallic multilayer systems have gained a great deal of research efforts in recent years due to their extraordinary mechanical properties, thermal stability and radiation damage resistance, as compared to their nanocrystalline counterparts. The complex incoherent interfaces formed between crystallographically dissimilar metals and the relative ease with which they can shear or transform from one metastable state to another and their interaction with dislocations gives rise to unique phenomena under high strain-rate deformation. Such interfaces can also effectively accommodate plasticity when subjected to shock loading conditions. A critical parameter to evaluate the damage tolerance of a material under shock loading conditions is defined as the ‘spall strength’ referred to as the peak tensile failure prior to failure. A better understanding of the role of interface on the predicted shock response requires an atomic scale understanding of the mechanisms of nucleation, evolution and interaction of defects during shock loading and failure of multilayered systems so as to tailor and optimize these nanolayered composites for damage-tolerant applications.
This study uses Cu/Ta laminate microstructures as a model system to investigate the shock deformation and spall failure behavior using molecular dynamics (MD) simulations. The effects of interface structures and crystallography (interface orientation relationship and layer spacing) and loading conditions (impact velocity and direction) on the dislocation evolution and spall failure are investigated. MD simulations suggest that the slip emission and transmission events depend strongly on the interface structure as well as the layer spacing of the laminate structures considered. The variations in defect evolution result in variations in the spall response of the laminates which is attributed to the nucleation, growth and coalescence of voids. The evolution of defect densities, the mechanisms of void nucleation and the links between the interface structure and spacing will be discussed.
2:45 PM - PM03.11.05
Radially Layered Multi-Material Struts for Increased Energy Absorption and Fracture Strain in Stiff Lattice Structures
Jochen Mueller 4 , Jordan Raney 1 , Jennifer Lewis 2 3 , Kristina Shea 4
4 Department of Mechanical and Process Engineering, ETH Zurich, Zurich Switzerland, 1 Department of Mechanical Engineering and Applied Mechanics, University of Pennsylvania, Philadelphia, Pennsylvania, United States, 2 John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States, 3 Wyss Institute for Biologically Inspired Engineering, Harvard University, Cambridge, Massachusetts, United States
Show AbstractHigh stiffness, high toughness, and low density are material properties that are typically mutually exclusive. Nature found ways to simultaneously achieve these properties through the introduction of material and geometric features spanning across multiple length scales. These features have been hard to replicate synthetically and specialized processes, such as freeze casting, yield a high anisotropy that is unsuitable for lightweight lattice structures. In this work, we develop a new, adaptable nozzle for the direct ink writing process that is tailored to lattice structures. The nozzle allows taking advantage of the fourth-order increase of stiffness with diameter by placing a brittle material on the outside and a flexible material on the inside of the struts. An interfacial layer separates the two materials and prevents diffusion and cracks from propagating into the core. The added mechanisms account for an increase in energy absorption of more than 100% when compared to conventional struts, while the stiffness remains mostly unaffected.
3:30 PM - *PM03.11.06
Fabrication of Nanocomposite through Diffusion Bonding under High-Pressure Torsion
Megumi Kawasaki 1 , Jae-il Jang 2
1 Mechanical, Industrial and Manufacturing Engineering, Oregon State University, Corvallis, Oregon, United States, 2 Materials Science and Engineering, Hanyang University, Seoul Korea (the Republic of)
Show AbstractLight-weight metals are conventional structural metals having excellent physical and mechanical properties and with good strength-to-weight ratios in the finished products. However, there may be an upper limit on the enhancement in mechanical properties when the processing is conducted directly on the alloy. Moreover, the fabrication of high-strength metals generally involves long-term processing conducted under extreme conditions using special facilities. Accordingly, this presentation demonstrates a simple and very rapid synthesis of metal matrix nanocomposites (MMNCs) in several Al hybrid systems which are achieved by processing stacked disks of the two pure metals by high-pressure torsion (HPT) at ambient temperature. These synthesized hybrid systems exhibit exceptionally high specific strength through rapid deformation-induced diffusion and the simultaneous formation of a few different intermetallic compounds. Experiments are conducted for demonstrating the essential microstructural changes of these MMNCs with increased straining by HPT and the evolution of small-scale mechanical properties, especially for evaluating the improvement in plasticity, by applying the novel technique of nanoindentation in these hybrid system after HPT. These new experimental findings suggest a potential for simply and expeditiously fabricating a wide range of MMNCs through HPT.
4:00 PM - PM03.11.07
Effect of Interfacial-Strength on Macroscopic Toughness and Strength of CNT-Silica Nanocomposites
Tengyuan Hao 1 , Md Hossain 1
1 , University of Delaware, Newark, Delaware, United States
Show AbstractIn this talk, I will explain the findings on atomistic investigation of mechanical properties (such as macroscopic strength and toughness) of CNT-Silica nanocomposite. We investigate the macroscopic toughness and strength of the nanocomposite collectively by controlling interfacial-strength. We also considered a range of atomistic architectures across different length scales to carry out this study. The results show that different interfacial-strength can extraordinarily change the macroscopic strength and toughness of the nanocomposite. There is a corresponding mathematical relationship between interfacial-strength and macroscopic strength as well as interfacial-strength and macroscopic toughness of CNT-Silica nanocomposite. In a certain range of interfacial-strength, we find that macroscopic toughness increases by 65% and macroscocpic strength increases by 34%. When interfacial-strength is high enough, continuing increase of interfacial-strength will not affect the macroscopic toughness and strength any further. On the other hand, when interfacial-strength is low enough, the macroscopic toughness and strength of CNT-Silica nanocomposite become insensitive to the changing of interfacial-strength.
4:15 PM - PM03.11.08
Graphene/Cu-Nanostructure Composite Based Mechanical Bonding Technology
Haozhe Wang 1 , Fengtian Hu 2 , Longlong Ju 2 , Wei Sun Leong 1 , Cong Su 1 , Ming Li 2 , Anmin Hu 2 , Jing Kong 1
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 , Shanghai Jiao Tong University, Shanghai China
Show AbstractGraphene has shown great potential as a diffusion barrier in many electronic fabrication process due to its chemical stability and high conductivity. Prior studies indicate that graphene can significantly slow down the formation of intermetallic compound (IMC) between two different types of metals, and hence, graphene has been considered as an ideal barrier layer for many electronic applications including 3D packaging. However, owing to graphene’s smooth surface with low friction coefficient, the bonding process cannot be performed by conventional industrial approaches such as vertical thermocompression bonding, thus all previous research efforts rely on metal deposition instead of the standard industrial process. In this work, we develop a mechanical bonding technology based on graphene/Cu-nanostructure composite. We first fabricate Cu nanocone array using a one-step electrochemical method that induces high stress on the Cu tip making its surface rougher. Subsequently, monolayer graphene synthesized via chemical vapor deposition (CVD) technique on was transferred on to the pre-fabricated Cu nanocone array forming the graphene/Cu-nanostructure composite (Gr/NCA). We note that ethylene-vinyl acetate (EVA) assisted transfer technique was adopted in this work to optimize the adhesion between graphene and Cu nanocone array [1]. Comparing to graphene on flat copper, our Gr/NCA technology can achieve effective bonding joint with satisfying shear strength (up to 1000 gf). Furthermore, we proved that the presence of monolayer graphene can effectively retard the growth rate of intermetallic compounds, compared to samples with pure Cu nanocone array. In addition, the shear strength of bonding joint with Gr/NCA is ~50% larger than the samples with pure Cu nanocone array, even after a 96 hours of ageing test. Remarkably, the bonding temperature used in our proposed technology here is 150 degree Celcius, which is much lower compared to the conventional welding approach. In short, we have devised a new mechanical bonding technology using graphene/Cu-nanostructure composite that is cost-effective and environmental friendly, useful for real industrial applications.
*Haozhe Wang, Fengtian Hu and Longlong Ju contributed equally to this work.
References:
[1] Jin-Yong Hong, Yong Cheol Shin, Ahmad Zubair, Yunwei Mao, Tomás Palacios,
Mildred S. Dresselhaus, Sung Hyun Kim, and Jing Kong*. A rational strategy for graphene transfer on substrates with rough features. Adv. Mater. 2016, 28, 2382–2392.
4:30 PM - PM03.11.09
First Principles Study of Adhesion and Mechanical Properties of Ceramic Diffusion Barrier Coatings for Nuclear Applications
Zhi-Gang Mei 1 , Sumit Bhattacharya 1 , Abdellatif Yacout 1
1 , Argonne National Laboratory, Lemont, Illinois, United States
Show AbstractZirconium nitride (ZrN) has been proposed as a diffusion barrier for U-Mo/Al dispersion fuel developed for future high performance research reactors. Atomic layer deposition (ALD) has been successfully used to deposit ZrN on U-Mo substrate. However, it was found that the ZrN coating not only showed signs of cracking right after the deposition process but spalled off with little external manipulation. Deposition of additional layer of alumina as interlayer in between the ZrN coating and the uranium substrate seemed to solve the problem of spallation. So far, it is clear why alumina interlayer can improve the bonding between ZrN coating and U-Mo particle. To this end, we investigated the interfaces formed between the diffusion barrier coatings and U-Mo substrate using first-principles calculations. The adhesion and mechanical properties of ZrN and alumina coatings were evaluated using a combination of first-principles calculations and fracture mechanics. We predicted the atomic structure, bonding, and ideal work of adhesion of the interfaces formed between the diffusion barriers and U-Mo substrate. Calculations show alumina coating produced a much stronger bond with the uranium surface when compared to direct zirconium nitride coating. The predicted elastic properties and ideal work of adhesion were also used to evaluate the interfacial fracture toughness of diffusion barrier coatings along different orientations. This work provides a useful guidance for selecting mechanically stable diffusion barriers and thermodynamically favorable synthesis conditions.
4:45 PM - PM03.11.10
High Strength, Ductile Nanostructured Al Alloys
Qiang Li 1 , Sichuang Xue 1 , Zhe Fan 1 , Jian Wang 2 , Shuai Shao 3 , Julia Greer 4 , Haiyan Wang 1 , Xinghang Zhang 1
1 , Purdue University, West Lafayette, Indiana, United States, 2 , University of Nebraska–Lincoln, Lincoln, Nebraska, United States, 3 , Louisiana State University, Baton Rouge, Louisiana, United States, 4 , California Institute of Technology, Pasadena, California, United States
Show AbstractHigh-strength, light-weight Al alloys have widespread applications for transportation industry. The best commercial Al alloys (typically age hardened) nowadays have a yield strength of ~ 0.7 GPa. In comparison, advanced high strength steels have tensile strength in excess of 1 GPa. In this presentation, we will describe the fabrication of nanostructured Al alloys. These Al alloys have strength exceeding 1 GPa, as revealed by nanoindentation and in-situ uniaxial compression experiments. The high strength of Al alloys derives from unique high-density favorable grain boundaries. The high strength, plasticity and strengthening mechanism have been validated by microscopy and molecular dynamic simulations