Symposium Organizers
Weizhong Han, Xi'an Jiaotong University
Ying Chen, Rensselaer Polytechnic Institute
Nan Li, Los Alamos National Laboratory
Christopher Weinberger, Colorado State University
Symposium Support
FEI, part of Thermo Fisher Scientific
NM9.1: <i>In Situ</i> Nanomechanics I
Session Chairs
Weizhong Han
Christopher Weinberger
Tuesday PM, April 18, 2017
PCC West, 100 Level, Room 102 C
11:30 AM - *NM9.1.01
Plasticity in Nano-Scale Heterogeneous Metallic Structures
Amit Misra 1
1 , University of Michigan–Ann Arbor, Ann Arbor, Michigan, United States
Show AbstractThis presentation will review the recent progress in the understanding of plasticity of heterogeneous metal-based composites. Laser-processed Al-based eutectics containing intermetallic phases will be used as model systems to elucidate plastic flow in nanoscale structures comprised of plastically heterogeneous phases. Nanomechanical testing and in situ TEM straining experiments will be used to characterize critical aspects of interface-dominated mechanical behavior in nanoscale composites such as unusually high flow strengths, high strain hardening rates and plastic co-deformability. The experimental results will be analyzed using atomistic modeling, dislocation theory and crystal plasticity. The conditions that lead to plastic co-deformation in soft/hard nano-composites will be highlighted.
12:00 PM - *NM9.1.02
Effects of Hydrogen on the Formation of Blister and the Dislocation Behavior of Al
Zhiwei Shan 1 , Degang Xie 1
1 , Xi'an Jiaotong Univ, Xi'an China
Show AbstractBlistering at metal surfaces after hydrogen attack was usually thought as a simple blown-up deformation process of oxide layer by H2 pressure underneath. By in situ observation of aluminum pillars in an environmental transmission electron microscope, we reveal that before the oxide deformation there exist a multi-step process of nucleation, growth, and coalescence of inward-bulging embryonic voids immediately beneath aluminum/oxide interface. Meanwhile, the detachment of Al metal from oxide layer exposes fresh metal surfaces, for which the blistering propensity are consistent with their surface diffusivities and are orientation dependent, i.e. {111}>{100}>{110}. This phenomenon could be a guidance to peeling off thin film and obtaining naked metal surface (1). In addition, we demonstrate that after exposing aluminum pillars to hydrogen, mobile dislocations can lose mobility, with activating stress more than doubled. Upon degassing, the locked dislocations can be reactivated under cyclic loading to move in a stick-slip manner. However, relocking the dislocations thereafter requires a surprisingly long waiting time of ~103 seconds, much longer than that expected from hydrogen interstitial diffusion. Both the observed slow relocking and strong locking strength can be attributed to superabundant hydrogenated vacancies; the role of hydrogen-vacancy complex is confirmed in our atomistic simulations. These findings provide key insights into plasticity and damage mechanisms underlying hydrogen embrittlement (2).
(1) Xie, D.-G.; Wang, Z.-J.; Sun, J.; Li, J.; Ma, E.; Shan, Z.-W., In situ study of the initiation of hydrogen bubbles at the aluminium metal/oxide interface. Nature Materials, 2015, 14 (9), 899-903.
(2) Xie D.-G.; Li M.; Li S.-Z.; Wang Z.-J., Gumbsch P.; Sun J.; Ma E.; Li J. & Shan Z.-W. Hydrogen effect on mobile dislocations in aluminum. Nature Communications, 2016.
12:30 PM - *NM9.1.03
High Cycle Fatigue Testing at Extremes of Sample Size and Frequency
Jicheng Gong 1 , Arutyun Arutyunyan 1 , Angus Wilkinson 1
1 , University of Oxford, Oxford United Kingdom
Show AbstractWe have developed a methodology for testing small volumes of materials to failure in the (very) high cycle fatigue regime. Focused ion beam (FIB) is used to cut triangular cross-section cantilevers into the surface of a bulk sample block. EBSD analysis is used to select grains and cantilever alignments that target specific slip systems. Cyclic deflections are excited in the cantilevers through vibration of the sample block using a high power ~20 kHz ultrasonic generator. Dynamic, elastic finite element analysis (FEA) simulations are used to design the micro-cantilever shapes so that applied vibration amplitudes (~2-50 µm) generate stress amplitudes of sufficient magnitude to study high cycle fatigue failure. The cantilevers are shaped with wider block of material at the free end so as to increase the inertia and thus stress amplitude. As well as providing the extreme accelerations (105 ms-2) required to generate stresses in the hundreds of MPa range, the high test frequency also allows testing into the extremes of the giga-cycle HCF regime. This ultra-small scale testing is complemented by cantilever tests at the meso scale (50-200 µm wide) using samples cut by laser micro-machining into thin metallic foils. Results from testing campaigns on Ti alloys (commercially pure, and Ti-6Al-4V) will be presented. The samples are monitored in situ using optical microscopy, while for more detail intermittent SEM is undertaken across the entire sample and shows that discrete slip events occur intermittently with significant blocks of cycles giving no detectable change in the sample surface features. Fatigue life responses of the micro-cantilevers will be compared to data for bulk samples taken from the literature, and size effects based on both sample dimensions and grain sizes will be discussed. The sample size effect will also be compared to size effect data for static bend strength in the micro-scale.
NM9.2: <i>In Situ</i> Nanomechanics II
Session Chairs
Tuesday PM, April 18, 2017
PCC West, 100 Level, Room 102 C
2:30 PM - *NM9.2.01
Nanoscale Strain Mapping of Individual Defects during In Situ Deformation
Thomas Pekin 1 2 , Colin Ophus 2 , Christoph Gammer 3 , Jim Ciston 2 , Andrew Minor 1 2
1 , University of California, Berkeley, Berkeley, California, United States, 2 , Lawrence Berkeley National Laboratory, Berkeley, California, United States, 3 , Erich Schmid Institute of Materials Science, Leoben Austria
Show AbstractRecent advances in local strain mapping using nanobeam electron diffraction (NBED) has demonstrated the ability to observe single defects and the strain fields around them at a resolution of single nanometers. In addition to measuring the strength of small-volumes, measuring the evolution of strain during plastic deformation is of great importance for correlating the defect structure with material properties. By observing dislocations, their strain fields, their movement under stress, as well as their interactions with each other, we aim to provide insight into fundamental mechanisms of deformation in metals. This work will highlight our latest results from in situ strain mapping in an Al-Mg alloy and stainless steel using both contact loading methods (such as in situ nanopillar compression and nanoindentation) as well as non-contact methods such as tensile straining. Our method of local strain mapping consists of recording large multidimensional data sets of nanodiffraction patterns during the test. The resulting dataset contains diffraction data for every point of the STEM image, from which strain maps can be extrapolated on a scale not previously possible during in situ deformation.
3:00 PM - *NM9.2.02
Spatiotemporal Slip Dynamics during Deformation of Microcrystals
Robert Maass 1
1 , University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Show AbstractPlastic deformation in metals proceeds intermittently in both space and time. In crystals these discrete processes are facilitated by collective dislocation rearrangements (dislocation avalanches). The spatiotemporal nature of plastic flow is difficult to assess due to its spatial confinement to the nano-scale and the short time scales. In this talk we will demonstrate how to trace the velocity profiles of dislocation avalanches in deforming fcc and bcc microcrystals. The measurements are supported by modeling and a careful assessment of the response dynamics of the device. We will discuss slip-size magnitude distributions, their involved time scales, slip-velocity distributions, slip-velocity profiles, and how loading modes affect these parameters. The experimental findings are used to test mean-field predictions for avalanches near the depinning transition. In particular, we will discuss differences of slip velocities in fcc and bcc crystals, how to rationalize the low valued slip velocities, and how they compare to known behavior of slip-band formation. It is further shown how intermittency may be tuned by the externally applied deformation rate and what implications this may have for macroscopic bulk plasticity.
3:30 PM - NM9.2.03
Small-Volume Aluminum Alloys with Native Oxide Shell Deliver Unprecedented Strength and Toughness
Shihao Li 1 , Weizhong Han 1
1 , Xi'an Jiaotong University, Xi'an China
Show AbstractMechanically robust nanoscale metallic materials are highly desirable in many miniaturized devices. However, the lack of strain hardening and controllable plasticity plagues such small-volume metals. Using Al-4Cu alloy as an example, here we show that a submicron-sized metallic material with ultrathin native oxide shell exhibits a high degree of deformation controllability, unprecedented strain hardening, size strengthening and toughness, in uniaxial tensile deformation. The metal/native oxide “composite” is easy to make, and the emergent properties extend well beyond the benchmark range known for metals in a normalized (i.e., dimensionless) strength-toughness plot. The origin of the combination of strengthening and plastic stability is that an intact ultrathin native oxide shell exerts a strong confinement on dislocation movement and annihilation, thereby breaking the envelope on dislocation storage and strain hardening achievable in small-volume metals.
3:45 PM - NM9.2.04
Microscale Fracture Experiments of Chevron-Notched Tungsten Cantilevers up to 700 °C
Bo-Shiuan Li 1 , David Armstrong 1 , James Marrow 1 , Steve Roberts 1 2
1 Department of Materials, University of Oxford, Oxford United Kingdom, 2 , Culham Centre for Fusion Energy, Abingdon, Oxon, United Kingdom
Show AbstractMicroscale fracture experiments are of great interest to the nuclear materials community, as it allows direct measurements of fracture toughness within thin ion-irradiated layers and significantly reduces the volume of radioactive samples required as compared to working with neutron irradiated samples.
Microscale chevron-notched tungsten cantilevers, fabricated and notched via focused-ion beam (Zeiss Auriga®), were tested using a variable temperature nanoindenter (Micro Materials NanoTest Xtreme®) under high vacuum environment (10-6 mbar) to prevent oxidation of specimen. Sample and tip temperature were carefully matched prior every test, as thermal drift must be minimised (<0.05 nm/s) to maintain good stability during the microscale fracture tests.
Tests at elevated temperatures (>300 °C) revealed the deformation mode of tungsten undergoes a brittle-to-ductile transition (BDT), with significant plastic deformation and stable crack growth as compared to room temperature tests. This is due to the thermally activated dislocation process; mobile dislocations shield the crack tip, hence making the brittle tungsten ductile. Given the stress intensity factor and crack length, the conditional fracture toughness (KQ) can be calculated using an elastic-plastic fracture mechanics (EPFM) approach. This is in good agreement with previous literature values in the same temperature regime, using macroscale four point bending experiments (5~40 MPam0.5).
NM9.3: High Entropy Alloy
Session Chairs
Tuesday PM, April 18, 2017
PCC West, 100 Level, Room 102 C
4:30 PM - *NM9.3.01
Understanding Solid Solution Strengthening in a High-Entropy Alloy by Micropillar Compression and Dislocation Analysis
Norihiko Okamoto 3 4 , Haruyuki Inui 3 4 , Easo George 1 2
3 , Kyoto University MSE Department, Kyoto Japan, 4 , Kyoto University ESISM, Kyoto Japan, 1 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 , University of Tennessee, Knoxville, Tennessee, United States
Show AbstractHigh-entropy alloys (HEAs) comprise a novel class of scientifically and technologically interesting materials. Among these, equiatomic CrMnFeCoNi, which forms a single-phase solid solution with the face-centered cubic (FCC) structure is noteworthy because it violates the strength-ductility and strength-toughness trade-offs. It is also of interest because of extreme compositional complexity and the difficulty of defining solvent and solute atoms in the conventional sense. In this talk we present results of single-crystal micropillar compression tests, polycrystalline compression tests, and post-compression dislocation analyses. The critical resolved shear stress (CRSS) depends on pillar size with inverse power-law scaling near the lower bound of FCC metals. Extrapolation to 20-30 µm pillar size yields a bulk CRSS of 33-43 MPa, which is 10 times that of pure nickel. We demonstrate a way to rationalize this high CRSS in terms of the calculated size misfits of the constituent atoms and the measured elastic constants of the HEA. After deformation, dislocations are smoothly curved without any preferred line orientation indicating no significant anisotropy in the mobilities of edge and screw segments. Planar ½<110>{111} dislocations dissociate into Shockley partials whose separations range from ~3.5-4.5 nm near the screw orientation to ~5-8 nm near the edge, from which we calculate stacking fault energy of 30 ± 5 mJ/m2. These microstructural aspects are used to gain a better understanding of the measured mechanical properties.
5:00 PM - *NM9.3.02
Dislocation Mechanisms and 3-D Twin Architectures Generate the Exceptional Strength, Ductility and Toughness of CrCoNi Medium-Entropy Alloy
Qian Yu 1 , Howard Sheng 3 , Easo George 4 , Scott Mao 5 , Robert Ritchie 2
1 , Zhejiang University, Hangzhou China, 3 , George Mason University, Fairfax, Virginia, United States, 4 , Ruhr University, Bochum Germany, 5 , University of Pittsburgh, Pittsburgh, Pennsylvania, United States, 2 , University of California, Berkeley, Berkeley, California, United States
Show AbstractThe combination of high strength and high ductility is hard to attain in metallic materials. Exceptions include materials that show twinning-induced plasticity. We apply quantitative in situ transmission electron microscopy (TEM) and aberration-corrected scanning TEM, to examine deformation twinning and dislocation behavior in an equiatomic solid solution CrCoNi medium-entropy alloy with coarse grains that exhibits one of the highest combinations of strength, ductility and toughness on record. From ab initio modeling, we show that it has a negative stacking fault energy and extremely high propensity for twinning. We find that a three-dimensional (3D) hierarchical twin network with the activation of three twinning systems is formed in individual coarse grains when this alloy is deformed that serves a dual function: conventional twin boundary (TB) strengthening involving blockage of dislocations impinging on the TB, coupled with the 3D high-density network of twins which offers additional pathways for dislocation motion by gliding along and cross-slip between the intersected TB-matrix interfacesinterfaces. Importantly, the twin architecture is stable and is not disrupted by such interfacial dislocation glide, such that it continuously serves as the source of both high strength and high ductility. As a result, strength, ductility and toughness are enhanced simultaneously.
5:30 PM - NM9.3.03
Atomic Scale Study of Twinning in Zirconium
Olivier MacKain 1 , Emmanuel Clouet 1
1 , CEA Saclay, Gif Sur Yvette France
Show AbstractPlasticity in zirconium, as well as in many other hexagonal close-packed metals, is controlled by the glide of dislocations with
Burgers vectors. Those dislocations can however not explain any deformation along the axis and at low temperatures twinning is activated to accommodate such a strain. In this work, we focus on the mechanisms controlling twin growth using atomistic simulations relying either on an empirical interatomic potential of the EAM type or on ab initio calculations. The four different twinning systems, which can be activated in zirconium depending on the temperature or the applied strain, are modeled. We first study the perfect twin boundaries showing the ability of the EAM potential to predict their structures and relative energies taking the ab initio calculations as a reference. We then focus on the disconnections, i.e. the twinning dislocations which are responsible of the twin growth. For a given twinning system, several disconnections of different Burgers vectors, different heights and different core structures exist. Considering all these disconnections, we calculate their formation and migration energies using the NEB method. The elastic interactions between the defects and their periodic images are computed using linear inhomogeneous anisotropic elasticity, allowing to extract disconnection core energies that are intrinsic properties of the disconnections, independent of the cell dimensions. We use this information to develop a kinetic model of twin growth and study the competition between the different growth modes under various stress states.5:45 PM - NM9.3.04
Understanding the Deformation Mechanism of the Individual Phases of Al0.7CoCrFeNi High Entropy Alloy (HEA) at Cryogenic Temperature
Adenike Giwa 1 , Karin Dahmen 2 , P.K. Liaw 3 , Julia Greer 1
1 Division of Engineering and Applied Sciences, California Inst of Technology, Pasadena, California, United States, 2 Department of Physics, University of Illinois Urbana-Champaign, Urbana, Illinois, United States, 3 Department of Materials Science and Engineering , The University of Tennessee, Knoxville, Knoxville, Tennessee, United States
Show AbstractThe uniaxial compression of nanopillars fabricated from single crystals of the 2 phases (FCC and BCC) present in Al0.7CoCrFeNi High Entropy Alloy (HEA) was carried out at 138 K. High yield strengths were observed in both phases with extensive plasticity. The “smaller is stronger” effect exists at 138 K which has also been observed at room temperature. The 700 nm-sized pillars of the FCC have a yield strength of 1.20 GPa in comparison to the 2 µm-sized pillars with a yield strength of 0.74 GPa while the 700 nm-sized pillars of the BCC have a yield strength of 2.16 GPa and the 2 µm-sized pillars has a yield strength of 1.54 GPa. The pronounced plasticity observed in the compression of the FCC phase pillars at 138 K is contrary to the discrete burst obtained at the room temperature experiments.
The deformation mechanism of the two phases differ at 138 K. The FCC phase is explained in terms of the activation of multiple slip systems as a result of dislocation motion and nanotwinning. This is further investigated by TEM analysis to show the twinning elements and the slip sizes of the serrations obtained from the stress strain signature during compression. The deformation mechanism of the BCC phase is explained by suppressed dislocation motion at low temperatures.
Symposium Organizers
Weizhong Han, Xi'an Jiaotong University
Ying Chen, Rensselaer Polytechnic Institute
Nan Li, Los Alamos National Laboratory
Christopher Weinberger, Colorado State University
Symposium Support
FEI, part of Thermo Fisher Scientific
NM9.4: Radiation Damage
Session Chairs
Wednesday AM, April 19, 2017
PCC West, 100 Level, Room 102 C
9:00 AM - *NM9.4.01
Radiation Response of Nanoporous and Nanotwinned Metals
Xinghang Zhang 1 , Jin Li 2 , Youxing Chen 3 , Haiyan Wang 1 , Mark Kirk 4 , Meimei Li 4 , Cheng Sun 5 , Kaiyuan Yu 6
1 , Purdue University, West Lafayette, Indiana, United States, 2 , Texas A&M University, College Station, Texas, United States, 3 , Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 4 , Argonne National Laboratory, Argonne, Illinois, United States, 5 , Idaho National Laboratory, Idaho Falls, Idaho, United States, 6 Department of Materials Science and Engineering, China University of Petroleum-Beijing, Beijing China
Show AbstractSevere high energy particle (neutron) and ion irradiation environment can introduce significant microstructural damage and consequent degradation of mechanical properties in irradiated metallic materials. It remains a scientific challenge to design advanced radiation tolerant materials. Numerous approaches have been applied to alleviate radiation damage. Here we will present some recent studies on enhanced radiation tolerance of nanostructured metallic materials, in particular nanoporous and nanotwinned metals. In situ heavy ion irradiation studies reveal direct evidence of defect-free surface interactions in nanoporous metals. Meanwhile high density twin boundaries prominently reduce the density of radiation induced defect clusters in nanotwinned Ag and Cu compared with their bulk counterparts. Defect migration kinetics (diffusivity of defect clusters) was compared between coarse grained and nanoporous metals. These studies provide insight towards understanding on the role of free surface and twin boundaries on alleviation of radiation damage in metallic materials. This research is funded by NSF-DMR- Metallic Materials and Nanostructures Program under contract no. 1643915.
9:30 AM - *NM9.4.02
Elastic Interaction between Nano-scale Defects in Irradiated Materials—Implications for Microstructural Evolution
Sergei Dudarev 1 , Adrian Sutton 2
1 , UK Atomic Energy Authority, Abingdon United Kingdom, 2 Department of Physics, Blackett Laboratory, Imperial College London, London United Kingdom
Show AbstractElastic interactions between defects formed in materials under irradiation play a subtle but
highly significant part in the dynamics of microstructural evolution. There are two statistical
aspects that make the problem particularly challenging: the scale-free size distribution of defects
generated by irradiation, with no clear transition between the point defect and mesoscopic dislocation
populations; and mobility laws highly sensitive to temperature and defect configuration, where diffusion
of point defects accompanied by growth and coalescence of mesoscopic dislocations occur as a result
of interaction between them. We derive expressions for the energy of elastic interaction between
nano-scale defects, such as crowdions, vacancies and vacancy clusters, and dislocation loops produced
in materials by irradiation. These equations are well suited to real-space simulations of dynamic
evolution of populations of interacting defects in an elastic continuum, where elastic interaction
between defects plays a part analogous to interatomic potentials in a molecular dynamics simulation.
We investigate the fundamental relation between elastic relaxation volumes of defects and dislocations,
determining the strength of elastic interactions, and radiation-induced swelling of materials.
10:00 AM - NM9.4.03
Microstructural Evolution and Self-Ion Damage in Nanocrystalline Tungsten Alloys
Olivia Donaldson 1 , Khalid Hattar 2 , Jason Trelewicz 1
1 , Stony Brook University, Stony Brook, New York, United States, 2 , Sandia National Laboratories, Albuquerque, New Mexico, United States
Show AbstractAt the core of designing advanced materials for harsh environments involving high temperatures, extreme stresses, and aggressive irradiation conditions lies unprecedented thermal stability. Refractory metals are inherently suited for extreme temperature applications due to their high melting points, and recent focus has been placed on engineering nanocrystalline structures into these materials to enhance other key properties such as strength and radiation tolerance. Significant insights into the underlying mechanisms have been gained through advanced in situ transmission electron microscopy (TEM) techniques, which enable precise probing of nanoscale grain and defect structures under extreme conditions. In this study, in situ TEM was employed to characterize microstructural evolution in nanocrystalline tungsten, tungsten-chromium, and tungsten-titanium thin films. Samples were prepared by magnetron sputtering and deposited to a nominal thickness of 20 nm with a mean grain size of 10 nm. Nanocrystalline structures in all three systems were evolved at temperatures over the range of 300 – 1000°C, and bright-field imaging was coupled with precession electron diffraction to ascertain detailed microstructural data in addition to grain size distributions. The nominally pure nanocrystalline tungsten films exhibited bimodal grain growth at intermediate annealing temperatures, which ultimately succumbed to the formation of an equiaxed nanocrystalline structure at a temperature of approximately 650°C. Coincident site lattice boundary fractions were mapped as a function of annealing temperature across both the abnormal and normal grain growth regimes. The addition of solute (Cr and Ti) stabilized nanocrystalline grain structures in the tungsten thin films, which was attributed to solute enrichment of the grain boundaries through scanning transmission electron microscopy. Self-ion irradiation damage was characterized through bombardment of the nanocrystalline films using 3 MeV W4+ ions in the in situ ion irradiation TEM at Sandia National Laboratories. Collective analysis of the resulting defect densities and microstructural characteristics revealed that the stabilization of nanocrystalline tungsten via grain boundary segregation has important implications for the design of radiation-tolerant alloy configurations.
10:15 AM - NM9.4.04
Quantification of the Role of Interfaces and Grain Boundaries in the Development of Radiation Tolerant Nuclear Materials
Pranav Suri 1 , James Nathaniel 1 , Bernard Gaskey 2 , Ian McCue 3 , Khalid Hattar 4 , Jonah Erlebacher 2 , Mitra Taheri 1
1 Materials Science and Engineering, Drexel University, Philadelphia, Pennsylvania, United States, 2 Materials Science and Engineering, John Hopkins University, Baltimore, Maryland, United States, 3 Materials Science and Engineering, Texas A&M University, College Station, Texas, United States, 4 , Sandia National Lab, Albuquerque, New Mexico, United States
Show AbstractGrain boundaries (GBs) are known as effective sinks for point defects created under irradiation, making them an attractive tuning parameter in order to engineer materials with superior radiation tolerance. Therefore, in the quest of advanced nuclear materials which are self-healing under irradiation and have longevity, nanocrystalline and ultrafine grain materials have gained much traction over the past decade, but it is not clearly understood yet how the defects manifest and annihilate themselves at the grain boundaries. Here, we describe through in situ ion irradiation TEM experiments the role of sinks in damage mitigation at the atomic-level by understanding the interaction of irradiation induced defect clusters and dislocation loops with GBs. We show the damage mitigation mechanism at the GBs and interfaces in BCC, FCC and BCC-FCC hetero-phase materials of varying grain sizes and quantify the efficiency of the various sinks. Using a combination of precision electron diffraction (PED) and in situ ion irradiation TEM experiments, we also examine the influence of local intrinsic and applied strain across the GBs and interfaces on the damage mitigation mechanism. Extension of such studies to understand the role of GB character in determining their sink efficiency will also be discussed. In summary, these studies are aimed to develop a clear and quantitative understanding of the efficiency of the defect sinks towards the absorption of irradiation induced defects and reveal the mechanism of the defect absorption at the sinks using the atomic-resolution TEM characterization.
10:30 AM - NM9.4.05
Effects of Annealing and Heavy Ion Irradiation on the Mechanical Properties of AlSc Alloys
Nisha Verma 1 , Sezer Ozerinc 2 , Sungeun Kim 1 , Robert Averback 1
1 Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 2 Mechanical Engineering, Middle East Technical University, Ankara Turkey
Show AbstractScandium additions to aluminum are known to increase its strength, stability and creep resistance. Sc has low solubility in Al, (0.38 at.% at eutectic temperature of ≈660°C), and Sc and Al forms an Al3Sc phase which readily precipitates from the supersaturated solid solution of Al and Sc. These hard precipitates are coherent with Al matrix due to small lattice mismatch of 1.2%. The high strength and high temperature stability of the AlSc microstructure possibly can be exploited for radiation resistance, where the fine precipitates provide the stable sinks for radiation-induced defects. However, the behavior of AlSc alloys under irradiation and associated mechanical behavior have not been much studied to date. In this work, we investigated the mechanical and microstructural properties of thin films of dilute Al-based Sc alloys. 600 nm thick, pure Al and Al-1.1%Sc films were prepared by magnetron sputtering for this work. The films were annealed in the range 25 °C – 250 °C and irradiated with 1.8 MeV Kr+ ions to doses up to 40 displacements per atom. The microstructure has been investigated with TEM and hardness was measured using nanoindentation. The addition of 1.1% Sc increases the hardness of nanocrystalline pure Al from 650 MPa to 2 GPa. Microstructural characterization by TEM reveals that the as-grown samples are homogeneous solid solutions of Sc in Al with grain size of ~100 nm. Subsequent heat treatment at 250°C induces precipitation of Al3Sc phase uniformly distributed with a size of ~20 nm. This precipitation is accompanied by a reduction in hardness to 830 MPa. The large increase in hardness upon the addition of Sc and its decrease upon precipitation suggests that in the nanocrystalline regime, solid solution strengthening is much more pronounced than precipitation strengthening, in agreement with previous work on dilute Cu alloys including Nb, Fe and Ta. The as-grown and annealed samples were further exposed to Kr irradiation at various temperatures to explore the competing effects of solute precipitation and irradiation induced mixing. Sc in the as grown sample remains in solid solution under irradiation at temperatures up to 150°C with a slight reduction in hardness to about 1.7 GPa (from 2.0 GPa), whereas the annealed samples show a reduced density of precipitates upon irradiation, due to radiation induced-mixing; the hardness is then increased to ≈1.5 GPa. In summary, Sc tends to form precipitates upon annealing and irradiation reverses this process through irradiation induced mixing. Hardness increases with increasing content of Sc in solid solution and can enhance the hardness of pure Al by a factor of 3.
NM9.5: Defect Microstructure
Session Chairs
Wednesday PM, April 19, 2017
PCC West, 100 Level, Room 102 C
11:15 AM - *NM9.5.01
Atomistic Study of Dislocations in Intermetallic Compounds
Jian Wang 1
1 , University of Nebraska–Lincoln, Lincoln, Nebraska, United States
Show AbstractPrecipitation-hardening mechanisms have been widely applied for the development of high strength and ductile metal-based alloys. Al-based structural alloys that contain Al-based intermetallic precipitates are potential candidates for structural applications at ambient and elevated temperatures because of their lightweight, four times lower density as compared to steel. Understanding characters of dislocations and their interactions and roles in mechanical behaviors is essential for developing and advancing the application of Al-based structural alloys in industry. Using atomistic simulations, we studied seven potential slip systems (110)<001>, (010)<001>, (310)<001>, (010)<100>, (110)<1-10>, (110)1/2<1-1 1> and (112)1/2<-1-11> in Al2Cu with body centered tetragonal structure. We found that three edge dislocations with Burgers vector <001> on glide planes (110), (010), and (310), show an extended core and are predicted to be glissile at room and moderate temperatures. Other four edge dislocations and screw dislocations show a condensed core, and exhibit significantly higher Peierls barrier for glide at room temperature. Furthermore, the interaction of dislocation dipole associated with slip system (110)<001> results in the climb of the extended-core dislocation at room temperature.
11:45 AM - *NM9.5.02
The Role of Interfaces on Plasticity in Dislocation Nucleation-Mediated Nanostructures
Jungho Shin 2 , Gunther Richter 3 , Thomas Cornelius 4 , Olivier Thomas 4 , Daniel Gianola 1
2 , University of Pennsylvania, Philadelphia, Pennsylvania, United States, 3 , Max Planck Institute for Intelligent Systems, Stuttgart Germany, 4 , Aix-Marseille University, Marseille France, 1 , University of California Santa Barbara, Philadelphia, Pennsylvania, United States
Show AbstractA straightforward strategy for reaching the ideal strength of crystalline metallic materials is to synthesize materials with a scarcity of defects. Bottom-up synthesis of nanostructures is an ideal means of approaching this limit, where nucleation of dislocations is a requirement in otherwise perfect crystals to facilitate plastic flow and mitigate brittle fracture. In this deformation mechanism regime where thermal fluctuations assist in the nucleation process, deterministic mechanical response gives way to probabilistic yielding with a strong temperature dependence and activation energies suggestive of surface self-diffusion as the rate-limiting step needed to promote displacive activity. We show mechanical deformation experiments using various in situ electron and X-ray probes on high quality single crystalline noble metal nanowhiskers and interrogate a new means of controlling mechanical response – by control of both external (free surfaces) and internal (planar defects) interfaces to mediate dislocation nucleation and ensuing plasticity.
12:15 PM - *NM9.5.03
Combining Statistical Electron Microscopy Measurements with Computational Simulations to Understand Twin/Grain Boundary Interactions in Pure Rhenium
Josh Kacher 1 , M. Arul Kumar 2 , Andrew Minor 3 4
1 , Georgia Institute of Technology, Atlanta, Georgia, United States, 2 Materials Science and Technology Division, Los Alamos National Laboratory, Albuquerque, New Mexico, United States, 3 Materials Science and Engineering, University of California, Berkeley, Berkeley, California, United States, 4 National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractOf the refractory metals, rhenium is of interest due to its high-temperature creep resistance and low temperature ductility. It is unusual among HCP materials in that its microstructural evolution during deformation is dominated by {11-21}-type twinning rather than the more commonly seen {10-12} twinning. I will present results combining statistical electron backscatter diffraction (EBSD) measurements, in situ transmission electron microscopy (TEM) deformation, and crystal plasticity Fast Fourier transform (FFT)-based simulations to investigate twin/grain boundary interactions in pure rhenium. Over one thousand twin/grain boundary interactions were isolated in the EBSD data and characterized in terms of shear vector and twin plane alignment across the boundary, revealing that the interactions were primarily dictated by the alignment of the twin plane across the boundary. The grain boundary disorientation angle was also shown to play an important role, with twin transmission across a boundary being significantly more likely in lower-angle grain boundaries than high-angle grain boundaries. In situ TEM nanoindentation experiments captured twin nucleation and propagation events as well as twin/twin interactions. It was seen that twin boundaries can act as either strong or weak barriers to twin propagation. Spatially resolved crystal plasticity based FFT model was employed to understand the local interaction between the twins and the grain boundaries. The accommodation of twinning shear was found to create a local stress concentration around the twin tip in the neighboring grain, acting as the driving force for twin-transmission. In agreement with the experimental observations, this driving force was found to decrease with increasing grain boundary disorientation angle.
12:45 PM - NM9.5.04
Thermally-Induced Microstructure Evolution in Nanocrystalline Metals
Ying Chen 1 , Zhanyang Chen 1
1 Materials Science and Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States
Show AbstractNanocrystalline metals are generally susceptible to microstructure evolution due to the high density of grain boundaries in them. While alloying is known to be able to stabilize nanocrystalline grains, alloying effect on kinetics in segregating systems is not quantitatively understood. Moreover, graded nanocrystalline materials with spatial grain size gradients, such as surface nanocrystalline materials and multilayered structures, are promising to achieve otherwise competing mechanical properties, but are susceptible to microstructure evolution due to the microstructural gradient and the high density of grain boundaries in them. This talk will present our modeling work on microstructure evolution in graded nanocrystalline alloys with spatial grain size gradients. Our study provides quantitative understanding of the concomitant evolution of solute distribution and the spatial grain size gradient.
NM9.6: Severe Plastic Deformation
Session Chairs
Ying Chen
Christopher Weinberger
Wednesday PM, April 19, 2017
PCC West, 100 Level, Room 102 C
3:00 PM - *NM9.6.01
Strength-Ductility Synergy in a Gradient Structure
Xiaolei Wu 1 , Yuntian Zhu 2
1 LNM, Institute of Mechanics, Chinese Aca Sci, Beijing China, 2 Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina, United States
Show AbstractStrong or ductile? For centuries engineers have been forced to choose one of them, not both as they would like to. This is because a material is either strong or ductile but rarely both at the same time. Here we report a grain size gradient structure in IF steel that can produce an unprecedented property combination. It is observed that the gradient structure increases the yield strength and maintain the large uniform elongation comparable to that of the coarse-grained counterpart. These superior mechanical properties were produced by high back stress, load transfer, and strong strain partitioning where the soft layers carried much higher plastic strain than hard layers. The strain hardening due to back stresses makes up for deficiencies of common forest hardening. Even with the presence of the yield-peak, the hardening rate due to back stresses up-turns in the transient to obtain large uniform elongation. Gradient structures exhibit a unique anti-banana-type yield strength vs ductility synergy.
4:30 PM - *NM9.6.02
Severe Microscale Deformation of Pearlite and Cementite
Steffen Brinckmann 1 , Caroline Fink 1 , Gerhard Dehm 1
1 , Max-Planck-Institut (MPIE), Dusseldorf Germany
Show AbstractMacroscale tribology is the interaction and evolution of micrometer asperities and microstructures. Wear resistant surfaces depend on understanding the evolution mechanisms and developing tailored surface layers. We investigate the severe microscale deformation mechanisms of pearlitic steel, i.e. the ferrite and cementite composite. On the one hand, we perform microtribology experiments using a diamond indenter and observe severe irreversible deformation of the cementite lamellae on the order of tens of percent.
On the other hand, we use microcantilever experiments with and without a pre-crack. The pre-cracked samples are used to quantify the fracture toughness and observe the fracture mechanisms. The samples without pre-cracks are used to determine the amount of irreversible deformation. In this overview talk, we will discuss the irreversible mechanisms, i.e. micro-fracture and plasticity, and shed light on the mechanisms that result in severe microscale deformation of single-phase and multi-phase metallic materials.
5:00 PM - *NM9.6.03
Self-Healing and Shape Memory Effects in Gold Microparticles through the Defects-Mediated Diffusion
Oleg Kovalenko 1 , Christian Brandl 2 , Leonid Klinger 1 , Eugen Rabkin 1
1 , Technion, Haifa Israel, 2 Institute for Applied Materials, KIT, Karlsruhe Germany
Show AbstractSome metal alloys subjected to plastic deformation can repair the inflicted damage and/or recover their original shape upon heating. These self-healing and shape memory effects rely on certain types of phase transformations in alloys. We report a new type of self-healing and shape memory in single crystalline faceted nano- and microparticles of pure gold plastically deformed with an atomic force microscope tip. We show that annealing of the deformed particles at elevated temperatures leads to nearly full restoration of their initial asymmetric polyhedral shape, which does not correspond to the global energy minimum. Our atomistic molecular dynamic simulations demonstrate that the shape recovery of the particles is controlled by the self-diffusion of gold atoms along the terrace ledges formed during the particles indentation. This ledge-guided diffusion leads to shape recovery by the irreversible diffusion process. We developed a semi-quantitative model of healing demonstrating a good agreement with the experimental data.
5:30 PM - NM9.6.04
Mechanical Grain Refinement vs Dynamic Recrystallization within Adiabatic Shear Bands in Steel and Copper during Impact
Solomon Boakye-Yiadom 1 , Nabil Bassim 2
1 , University of Waterloo, Waterloo, Ontario, Canada, 2 Mechanical Engineering, University of Manitoba, Winnipeg, Manitoba, Canada
Show AbstractThe manifestation of damage in materials deformed at high strain rates and large strains such as impact is the formation of narrow bands of extreme strains known as Adiabatic Shear Bands (ASBs). These ASBs precede crack nucleation which leads to catastrophic failure during subsequent deformation. It has been shown that the extent of deformation and associated conversion of plastic work to heat during dynamic loading is adequate to produce new recrystallized grains in ASBs. Hence dynamic recovery/recrystallization is widely accepted as a mechanism of formation of ASBs. However, recent studies suggest that the formation of ASBs may be as a result of multiple mechanical grain refinement which starts with the emergence of dislocations depending on the imposed local strain and strain rate. In the current study, pre-deformation and post-deformation microstructure characterization was conducted on tempered 4340 steel and commercial pure copper specimens under impact at room and high temperatures (25°C≤ T ≥ 600°C) to determine the mechanism that results in the final structure observed within ASBs. The microstructure of the ASBs observed in the tempered steel specimens can be considered as a concurrent layering of microstructures initially driven by dislocations. Conversely, the ASBs in the copper specimens evolved by the sequential occurrence of dislocation multiplication, dislocation cell formation and dynamic recovery/recrystallization. It is demonstrated that the observed recrystallized grains within some of the shear bands may be an after-effect of the rise in temperature during impact.
NM9.7: Poster Session
Session Chairs
Thursday AM, April 20, 2017
Sheraton, Third Level, Phoenix Ballroom
9:00 PM - NM9.7.01
Stress Corrosion Cracking and Polarization Test Analysis of Al-Mg-Zn Alloys by Homogenization
InKyu Choi 1 , Sangho Kim 1 , Suho Zo 1
1 , Korea University of Technology and Education, Cheonan Korea (the Republic of)
Show AbstractIn this study, we have investigated the effect of SCC behavior by homogenization. All samples for homogenization were taken from the center of the ingot with the dimensions of 10 cm x 10 cm x 10cm. The samples were homogenized at 400 and 450a'' for 3, 6, 12, 24 and 36h, respectively. Then the samples were observed by optical microscope, scanning electron microscope and transmission electron microscope. The polarization-test of the Al-Mg-Zn alloy was studied using an anodic polarization test in 1M NaCl solution at room temperature. Polarization range condition of the experiment were form −0.3V to −1.3V with a 0.2 mV scanning speed. Also, SCC was studied by slow strain rate test. This showed SCC and polarization test much better result in corrosion after homogenization. The cause of result was mainly attributed to continuous the inter-granular precipitates β phase which could make a galvanic corrosion on the aluminum base. Also, homogenization plays a very important role in the dissolution of the residual phases. Therefore, homogenization can be one of corrosion improvement methods.
9:00 PM - NM9.7.02
Electrodeposition of Ni-Mo Defect-Free Alloy from Ammonium-Citrate Electrolyte in Pulse Current Mode
Dmitry Suvorov 1 , Sergey Karabanov 1 , Yulia Stryuchkova 1 , Evgeny Slivkin 1 , Gennady Gololobov 1 , Dmitry Tarabrin 1 , Nikolay Rybin 1
1 , Ryazan State Radioengineering University, Ryazan Russian Federation
Show AbstractElectrolytic Ni-Mo alloy has broad application due to high erosion resistance, heat resistance, high mechanical strength and durability. Besides, its catalytic properties in relation to hydrogen evolution reaction in acid media are known.
The traditional method of obtaining coatings by nickel-molybdenum alloy is the method of its electrochemical deposition from the solutions containing nickel and molybdenum salts in direct current mode. The electrolyte composition and deposition parameters determine the alloy structure parameters and, accordingly, its functional properties. The main problem is the coating defect formation in the form of cracks considerably worsening coating functional properties and being the reason for its delamination. The search of ways of structure control and obtaining coatings without cracks is important.
The paper presents the results of experimental studies of coating synthesis of Ni-Mo alloy by the electrodeposition from ammonium-citrate electrolyte in pulse current mode. The current density of direct polarity pulse changed within 2-9 A/dm2, the current density of reversed polarity varied within 0.1-0.5 A/ dm2, the pulse duration varied over a wide range of 10-500 ms. Potentiodynamic polarization curves in ammonium-citrate electrolyte for a nickel substrate, the SEM images of Ni-Mo alloy surface deposited on a nickel substrate are received. The data on morphology change of the coating surface at various parameters of deposition current pulses is obtained. It is shown that the most dense and smooth coatings of electrolytic nickel-molybdenum alloy from ammonium-citrate electrolyte are obtained at electrolysis pulse mode. The parameters of electrodeposition mode at which the defect-free structure and minimum coating roughness is reached are determined. It is established that the electrodeposition mode in the studied parameter range does not influence the percentage of components in the deposit.
The obtained results are of considerable practical importance for synthesis of Ni-Mo functional coatings.
9:00 PM - NM9.7.03
Failure of Granular Boron Carbide under Extreme Loading
Matthew Serge 2 , Michael Homel 3 , Jason Loiseau 4 , Timothy Walter 5 , Pouyan Motamedi 1 2 , Calvin Lo 2 , Eric Herbold 3 , Andrew Higgins 4 , Tomoko Sano 5 , James Hogan 2
2 , University of Alberta, Edmonton, Alberta, Canada, 3 , Lawrence Livermore National Laboratory, Livermore, California, United States, 4 , McGill University, Montreal, Quebec, Canada, 5 , Army Research Laboratory, Aberdeen Proving Ground, Maryland, United States, 1 , National Institute for Nanotechnology, Edmonton, Alberta, Canada
Show AbstractBoron carbide is a common component of both personal and vehicle composite anti-ballistic armor plating. Plate samples have been well-studied from a ballistics perspective, but further energy dissipation can be achieved by fragment failure. In place of studying penetration response in-situ, a fundamental study was performed on boron carbide powder, first sieved between 125 and 150 um, then tested via the thick-walled cylinder (TWC) technique. These experiments were aimed to determine the effect of high strain rate coupled shear and shock loading on the powder, as well as to establish the granular response and damage under two distinct loading conditions (global strains). Recovered samples were analyzed and characterized via optical and scanning electron microscopy. X-ray computed tomography scans were used in conjunction with steel tracer particles mixed in with the boron carbide powder to capture particle motion over the domain of the experiment, and then compared to detailed mesoscale simulations. The characterizations of boron carbide powder were compared to simulations and experimental geometries to determine dominant granular failure mechanisms.
9:00 PM - NM9.7.04
Radiation Stability of Metal Nanowires
Sergey Bedin 1 , Fedor Makhin'ko 1 , Vladimir Ovchinnikov 1 4 , Nikolay Gerasimenko 2 1 , Dmitri Zagorskiy 3 1
1 , Institute of Electrophysics, Ural Branch, Russian Academy of Sciences, Yekaterinburg Russian Federation, 4 , El'tsin Ural Federal University, Yekaterinburg Russian Federation, 2 , National Research University of Electronic Technology (MIET), Moscow Russian Federation, 3 , Institute of Crystallography, Moscow Russian Federation
Show AbstractThe aim of this work is to investigate the radiation stability of metal nanowires (NWs).For doing this NWs of pure nickel and iron–nickel Fe0.56Ni0.44 alloy were fabricated by the template synthesis technique. Commercial track membranes with a pore diameter from 0.03 to 0.1 μm (JINR, Dubna) were used as template matrixes. A Watts electrolyte was used to prepare nickel NWs, at an electrolyte temperature of 50–60°C. The Fe0.56Ni0.44 alloy was deposited from the composite electrolyte.
After electrodeposition NW arrays were separated from the polymer template matrix. Then these samples were irradiated with continuous Ar+ ion beams using an ILM-1 implanter equipped with a PULSAR-1M technological ion source based on a low-pressure glow discharge with a hollow cold cathode, which can operate in the continious and pulsed-periodic modes (Sbeam ~ 100 cm2; the energy and ion current density in the continuous mode were varied in the following ranges: E = 5–50 keV, j = 10–500 μA/cm2). NWs were also irradiated with Ar+ and Xe+
SEM investigation demonstrated that at a fluence of 1017 cm-2 and an irradiation time of 1 min , melted NW tops are observed. An increase in the fluence to 5×1017 cm-2 (irradiation time of 5 min with a step of 1 min) results in melting of a NW bundle up to its middle. A further increase in the fluence causes subsequent melting and deformation of NWs. Irradiation with heating (5 min) leads to the melting of the all surface of a NW bundle. The wires are less melted inside the bundle.
The dependence of this effect on wires diameter was also found and investigated. Melting of nanowires can be explained by the formation of thermal spikes under irradiation with heavy ions. They are almost spherical regions of dense cascades of atomic displacements with a typical diameter of 5–10 nm (about 10 nm to Ar+ and 7 nm for Xe+, thermalized for 10–12 s (cooling time of ~10-11), reaching temperatures of 3000–5000 K and above. The average depth at which these regions are formed is about 5–10 nm at an ion energy of 20 keV.
Since the energy release per atom of the cascade is significantly higher in the case of Xe+ than that of Ar+ [4], SEM shows more significant bending of nanowires with the formation of knots (buds) and even branches under Xe+ ion irradiation due to the possible splashes of the thermal peak regions out of the nanowires. Covering of adjacent nanowires with molten metal is possible.
As a result, the study showed that under both Ar+ and Xe+ ion irradiation conditions (E = 20 keV, j = 300 μA/cm2, fluences of 1016–1018 cm-2), NWs are deformed and melted even upon slight beam heating (to 150°C). The effect of Xe+ ion irradiation is more pronounced.
The conclusion about the low radiation stability of the NWs under used Ar+ and Xe+ ion irradiation conditions can be drawn.
Acknowledgments. This work was supported by the Russian Scientific Foundation, project no. 15-19-10054. Authors also thank Dr.V.Artemov (IC RAS) for SEM.
9:00 PM - NM9.7.05
Effect of Bx (0 < x < 10) on a Fe50Mn30Co10Cr10 High Entropy Alloy on Wear Resistance Produced by Laser Cladding
Jose Aguilar Hurtado 1 , Alejandro Vargas 1 , Dario Zambrano Mera 1 , Rodrigo Palma 1
1 , Universidad de Chile, Santiago Chile
Show AbstractHigh Entropy Alloy (HEAs) coatings (Fe50Mn30Co10Cr10) were prepared over low carbon steel (ASTM A36) using laser cladding process. The effect of boron (0 < x < 10) over microstructure of the coating was studied. Coating behavior against abrasive wear was evaluated and compared to uncoating substrate low carbon steel (ASTM A36, ≤ 0.26C, 0.8-1.2Mn, ≤0.4Si, ≤0.04P, ≤0.05S, Bal. Fe). The microstructure of the materials was analyzed by optical microscopy, scanning electron microscopy, and X-ray diffraction. The microhardness of the coating was also measured. Wear testing was carried out following a procedure according to the ASTM G65 Standard. The results showed that there was significant effect of the boron content on abrasive wear behavior of the Fe50Mn30Co10Cr10 coating due to the volume fraction of boride precipitates increment as the boron content increases. The Fe50Mn30Co10Cr10 coatings produced by laser cladding process showed better wear resistance compared to the low carbon steel, indicating that this process could be used to generate more resistant surfaces against abrasive wear and reduce these problems preserving the properties of parts under severe abrasive conditions.
9:00 PM - NM9.7.07
Fabrication of Random Nano Crack Assisted Bundled Ag Nanowire Network for Transparent Flexible Conductor
Jinwook Jung 1 , Dongkwan Kim 1 , Habeom Lee 1 , Phillip Won 1 , Jin Hwan Lee 2 , Young Suh 1 3 , Seung Hwan Ko 1
1 , Seoul National University, Seoul Korea (the Republic of), 2 Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, Michigan, United States, 3 , Samsung Electronics Co., Ltd, Gyeonggi-do Korea (the Republic of)
Show AbstractA metallic network based foldable transparent electrode was fabricated by utilizing random nanocrack formed on silicon substrate. Original random patterns are prepared from controlled random cracking of high-stress silicon nitride on the silicon substrate, and employed as repetitively usable master molds with independently controllable pattern density and linewidth. Short silver nanowires are subsequently placed in the random crack channels to form bundled silver nanowire network. The nanowire network are transferred to the polymer substrate with UV curable epoxy resin. The resultant flexible and transparent conductor, spanning over wafer scale at high reproducibility, not only exhibits enhanced mechanical robustness upon repeated bending or scratching, which often occurs when used as touch-screen panel, but also is free from the moire pattern roblem due to the random nature of nanowire bundle patterns.
9:00 PM - NM9.7.08
Nanocrystalline Growth Mechanisms in High Speed Electrodeposition of Ni-Co Films on Untreated Titanium
Mohammad Hussein 1 , Kan Xie 2 , Haozhi Dong 2 , Virginia Ayres 2
1 Faculty of Construction, Engineering and Built Environment, Birmingham City University, Birmingham United Kingdom, 2 Electrical & Computer Engineering, Michigan State University, East Lansing, Michigan, United States
Show AbstractTitanium is a metal that finds use in a wide variety of applications as a structural material in aircrafts, engines, missiles, bicycles and load-bearing bone prostheses. In many applications, it is desirable to electrodeposit a coating with specific properties required for local interactions. As soon as titanium is exposed to the atmosphere, a thin tenacious oxide film forms almost immediately and conventional strategies for successful adhesion involve oxide film removal (surface activation) followed by surface capping with a sacrificial layer. Pretreatment methods are dangerous, time-consuming and environmentally unfriendly. A new and innovative process for direct electrodeposition of Ni-Co alloy on titanium surfaces without any pretreatment or displacement reaction has recently been reported [1]. Deposition of nanocrystalline nickel throughout the entire film growth process plays a critical role. Investigations of the non-columnar growth mechanism(s) that result in high-speed adhesive coating formation are presented.
[1] Hussain, MS. Direct Ni-Co alloy plating of titanium alloy surfaces by high speed electrodeposition. Trans Inst of Metal Finishing 90 (2012) 15. doi: 10.1179/174591911X13188464808876
9:00 PM - NM9.7.09
Modelling and Simulation of Microstructural Evolution in Zr Based Bulk Metallic Glass Matrix Composites during Solidification
Muhammad Musaddique Ali Rafique 1 , Dong Qiu 1 , Mark Easton 1
1 School of Engineering (Aerospace, Mechanical and Manufacturing Engineering), RMIT University, Carlton, Victoria, Australia
Show AbstractBulk metallic glass and their composites are unique new materials which have superior mechanical and structural properties as compared to existing conventional materials. Owing to this, they are potential candidates for tomorrow’s structural applications. However, they suffer from disadvantages of poor ductility and little or no toughness which render them brittle and they manifest catastrophic failure on the application of force. Their behavior is dubious and requires extensive experimentation to draw conclusive results. In present study, an effort has been made to overcome this pitfall by simulation. A quantitative mathematical model based on KGT theory has been developed to describe nucleation and growth of second phase dendrites from melt in glassy matrix during solidification. It yields information about numerical parameters necessary to understand the behavior of each individual element in multicomponent sluggish slurry and their effect on final microstructural evolution. Model is programmed and simulated in MATLAB®. Its validation is done by comparison with identical curves reported in literature previously for similar alloys. Results indicate that the effect of incorporating all heat transfer coefficients at macroscopic level and diffusion coefficients at microscopic level play a vital role in refining the model and bringing it closer to actual experimental observations. Two types of hypo and eutectic systems namely Zr65Cu15Al10Ni10 and Zr47.5Cu45.5Al5Co2 respectively were studied. Simulation results were found to be in good agreement with prior simulated and experimental values.
Symposium Organizers
Weizhong Han, Xi'an Jiaotong University
Ying Chen, Rensselaer Polytechnic Institute
Nan Li, Los Alamos National Laboratory
Christopher Weinberger, Colorado State University
Symposium Support
FEI, part of Thermo Fisher Scientific
NM9.8: Stress Corrosion Cracking
Session Chairs
Thursday AM, April 20, 2017
PCC West, 100 Level, Room 102 C
9:00 AM - *NM9.8.01
New Insights into Processes Driving Irradiation Assisted Stress Corrosion Cracking
Gary Was 1 , Drew Johnson 1 , Ian Robertson 2 , Diana Farkas 3
1 , University of Michigan, Ann Arbor, Michigan, United States, 2 , University of Wisconsin, Madison, Wisconsin, United States, 3 , Virginia Tech, Blacksburg, Virginia, United States
Show AbstractThe combination of radiation and a chemically aggressive environment gives rise to unique deformation modes and equally unique degradation modes such as irradiation assisted stress corrosion cracking. IASCC occurs in austenitic alloys exposed to irradiation while under stress in high temperature water. The mechanism is not well understood, but recent evidence has pointed to the interaction between dislocation channels and grain boundaries as a key factor driving the degradation. More specifically, the high local elastic stress at dislocation channel-grain boundary intersections is believed to be the key factor in crack nucleation. Yet very few sites result in crack nucleation. This talk will examine the response of irradiated austenitic stainless steels to stress in high temperature water. The nature of the dislocation channels and of the grain boundaries themselves on the cracking behavior will also be discussed in an effort to understand the selectivity of crack nucleation.
9:30 AM - *NM9.8.02
Environmentally-Induced Degradation of Coherent Twin Boundaries
Matteo Seita 2 , Michael Demkowicz 1
2 School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore Singapore, 1 , Texas A&M University, College Station, Texas, United States
Show AbstractCoherent twin boundaries (CTBs) are frequently thought to be the grain boundaries most resistant to environmentally-induced degradation in FCC metals. We use in situ tensile testing in a scanning electron microscope to investigate intergranular fracture in hydrogen-charged Ni-base alloys and find that CTBs are in fact preferential sites for crack initiation in these materials. Using a large experimental database of cracked CTBs and a specially-developed statistical inference method, we find that the conditions for fracture along these boundaries involve simultaneous mode-I loading and slip along the CTB plane. Our findings indicate that—far from being universally degradation-resistant—CTBs may be a material’s weakest links under certain environmental conditions.
10:00 AM - NM9.8.03
Fracture Path Analysis of Sodium Induced Embrittlement of 304L Stainless Steel
Bassem Barkia 1 , Samuel Hemery 3 , Jean-Louis Courrouau 2 , Thierry Auger 1
1 , CNRS/CentraleSupélec, Chatenay Malabry France, 3 , Institut P'/ENSMA, Poitiers France, 2 DEN/DANS/DPC/SCCME, CEA, Gif-sur-Yvette France
Show AbstractLiquid metal Embrittlement of austenitic stainless steels presents a challenge to fracture analysis due to their intricate microstructure. This often prevents correlating fracture surface with microstructural features by standard scanning electron microscopy fractographic analysis. Fracture micro-mechanisms and crack path of embrittled austenitic steel 304L by liquid sodium at 573 K are investigated down to the nanoscale. TEM/Fib/orientation mapping analyses below the fracture surface and higher scale EBSD mapping show that abundant martensitic transformation (γ-->α) and twinning occur during deformation of austenite. The preferential crack path is intergranular (γ/γ and α/α interfaces) with some evidence of transgranular fracture. We therefore conclude that these transformations play a major role in the fracture process. We highlight the need to characterize fracture surfaces with the underlying nanostructure.
10:15 AM - NM9.8.04
Oxygen Embrittlement in Niobium
Pingjiong Yang 1 , Jiewen Zhang 1 , Weizhong Han 1
1 , Xi’an Jiaotong University, Xi'an China
Show AbstractOxygen can be easily absorbed by niobium at elevated temperature and leads to severe oxygen embrittlement, which limits it application greatly. However, the origin of oxygen embrittlement in niobium is still unclear. Here, we found that a small amount of oxygen charging can dramatically increase the strength and reduce the plasticity of pure niobium. Pure brittle failure after yielding during tension was found in niobium containing oxygen, in contrast to the dramatic ductility of pure niobium. Dislocation slip localization along {110} plane formed beneath the fracture surface and near the crack tip. Furthermore, in situ tensile tests under TEM reveal that niobium containing oxygen tends to slip localization and failure abruptly along {110} plane. These studies suggest that dislocations can be quickly pinned by oxygen after nucleation, which induces deformation localization on ‘weak’{110} plane, thus causing quasi-brittle fracture under mechanical loading. Our findings are expected to shed new light on how to tailor advanced antioxidant niobium alloy.
10:30 AM - NM9.8.05
Character Dependence of Grain Boundary Corrosion in Aluminum
Ali Sangghaleh 1 , Matteo Seita 2 , Michael Demkowicz 1
1 , Texas A&M University, College Station, Texas, United States, 2 , Nanyang Technological University, Singapore Singapore
Show AbstractGrain boundaries (GBs) are susceptible to corrosion in many materials. However, the dependence of GB corrosion susceptibility on GB crystallographic character is not yet fully understood. We present a joint experimental/modeling study of this dependence in polycrystalline aluminum. We determine the complete crystallographic character of hundreds of individual GBs using a specially developed, non-destructive experimental technique. Upon exposure to acid, certain GBs corrode while others are unaffected. Corrosion appears to preferentially attack GBs formed by joining specific, low-index facets of the neighboring grains. We further analyze the structure of these GBs using the Arrangement of Interface Dislocation Arrays (AIDA) tool, which models GB structure in terms of arrays of intrinsic dislocations and relate the distribution of corroded GBs to the crystallographic texture of our sample. Insights gained from this study enable higher accuracy predictions of corrosion susceptibility in aluminum polycrystals based on their GB character distributions.
10:45 AM - NM9.8.06
Three-Dimensional Maps and Models of Helium Nanobubbles in a Palladium Alloy
Norm Bartelt 1 , Xiaowang Zhou 1 , David Robinson 1 , Suzy Vitale 1 , Joshua Sugar 1 , Kirt Shanahan 2
1 , Sandia National Laboratories, Livermore, California, United States, 2 , Savannah River National Laboratory, Aiken, South Carolina, United States
Show AbstractThe formation of nanoscale helium bubbles in metals is a common effect of exposure to radiation and radioactive substances. The rapid radioactive decay of tritium absorbed in palladium leads to an extreme, well-known example of this. The precise mechanisms by which He bubbles nucleate and grow is still uncertain, however. One way of extracting information about bubble growth is to analyze the configuration of the bubbles observed by electron microscopy. For example, a measurement of the distribution of bubble separations gives information about how bubble nucleation is affected by the presence of previously nucleated bubbles. Unfortunately it is difficult to obtain such distributions from the 2D images that currently exist. In this paper we show how 3D imaging by electron tomography of tritium generated He bubbles in a palladium-nickel alloy can provide detailed information about bubble size and spacing in samples with high bubble density. Our palladium-nickel alloy sample (4.8 atom % Ni) contained tritium for 3.8 years. We removed the tritium to a few tens of microcuries per gram using cycles of exposure to deuterium gas and vacuum without significant heating of the sample. A section of the sample was prepared in a tip geometry using focused ion beam milling, and tomography was performed using an aberration-corrected electron microscope. This has allowed for reconstruction of a three-dimensional image of several thousand cubic nanometers of the sample, and determination of the size and spacing distribution of the bubbles. We have extended previously published theoretical models of bubble nucleation and growth [DF Cowgill, Fusion Sci. Tech. 48 539 (2005)] to three dimensions in order to predict those distributions and compare to experimental results. This comparison suggests that, contrary to prior belief that nucleation ceases shortly after initial exposure to tritium, a significant population of bubbles is nucleated at later times.
Sandia National Laboratories is a multi-mission laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. Work at Savannah River National Laboratory was performed under contract number DE-AC09-08SR22470 with the U.S. Department of Energy (DOE) Office of Environmental Management (EM). We acknowledge the contributions to this work by Lynn Bouknight.
NM9.9: Superalloy
Session Chairs
Nan Li
Christopher Weinberger
Thursday PM, April 20, 2017
PCC West, 100 Level, Room 102 C
11:30 AM - *NM9.9.01
New Insights into Rate Limiting Deformation Processes in Ni-Base Superalloys
Tim Smith 1 , Ashton Egan 1 , Maryam Ghazisaeidi 1 , Steve Niezgoda 1 , Yunzhi Wang 1 , Michael Mills 1
1 , The Ohio State University, Columbus, Ohio, United States
Show AbstractPolycrystalline Ni-based superalloys are vital materials for disks in the hot section of aerospace and land-based turbine engines due to their exceptional microstructural stability and strength at high temperatures. In the drive to increase operating temperatures and hold times in these engines, hence increasing engine efficiency and reduction of carbon emissions, creep properties of these alloys becomes increasingly important. At these higher temperatures, new deformation modes become active. Twinning and stacking fault shearing are important operative mechanisms in the 600-800°C temperature range. Advanced characterization techniques--based on scanning transmission electron microscopy using diffraction contrast imaging, high resolution imaging, and energy dispersive spectroscopy--have been used to gain new insights into these mechanisms and the rate-limiting processes during high temperature deformation. Several alloy compositions and microstructure variants of commercial disk alloys are being explored to enhance creep behavior models and provide insights that can lead to higher temperature capabilities in these alloys.
12:00 PM - NM9.9.02
Migration of Recrystallization Grain Boundary during High Temperature Creep in a Directionally Solidified Superalloy
Guang Xie 1 2 , Li Wang 1 , Langhong Lou 1 , Jian Zhang 1 2
1 , Institute of Metal Research, Chinese Academy of Sciences, Shenyang China, 2 , Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang China
Show AbstractRecrystallization (RX) caused by residual strains in directionally solidified (DS) Ni-base superalloys is a well-known issue in the investment casting industry. It has been reported that a certain volume of RX may dramatically reduce the creep rupture strength of the DS alloys. However, no microstructural evolution of RX during creep has been carried out so far. The aim of our present paper is therefore to study the migration of RX grain boundary during high temperature creep of DS superalloy, trying to explore the reason about the migration of RX grain boundary during creep and its effect to the creep.
Plates were cut from the DS superalloy slabs and indented on one side using a Brinell hardness tester with different load. Local RX occurred when the plate-like specimens were subject to the standard heat treatment. The indentation was then carefully removed by grinding. Based on our previous experimental data, different volume (depth) of the residual local RX on the plates was obtained by controlling the grinding process. Then the creep rupture tests of specimens with local RX were carried out at 980 oC, 235 MPa.
After creep rupture test, the phenomenon of migration of recrystallization grain boundary was found. The morphology of cellular RX was observed in the region which RX grain boundary passed through. The longer the creep rupture life, the longer the migrating distance of RX grain boundary, and an almost linear relationship between the migration distance and the creep rupture life was found.
The RX grain boundary mainly moved along the normal direction of the applied tensile stress. The reason why the migration of RX grain boundary occurred was discussed. After long term aging at high temperature, only g' coarsening was found along the RX grain boundary, migration of RX grain boundary was not observed. Therefore, applied stress played an important role in the migration of RX grain boundary. The alloying elements diffusion of Al and Cr along the RX grain boundary induced by applied stress and high temperature may be result in the migration of RX grain boundary. Finally, migration of these RX grain boundaries may be beneficial to the propagation of cracks produced at transverse RX grain boundary.
12:15 PM - NM9.9.03
Liquid Metal Embrittlement with Mercury of Austenitic Steels
Thierry Auger 1 , Bassem Barkia 1
1 , CNRS/ECP, Chatenay Malabry France
Show AbstractA comparative study of embrittlement by liquid mercury of stainless steels is carried out with three different steels presenting different content of nickel (304L, 316L and 316L(N)).
A large difference in the sensitivity of these steels to LME is found indicating a key ingredient in the sensitivity. EBSD mapping on transverse cuts from the fracture surface as well as FIB lamella sampling were carried out showing a strong tendency for deformation induced martensitic transformation (γ-->α) as well as twinning. Deformation induced transformations tendency correlates well with the LME sensitivity. At the microstructural scale, fracture proceeds along deformation induced interfaces making it easier to understand the immunity of some steels to LME.
12:30 PM - NM9.9.04
TaC Precipitate Strengthening in Co-Re Alloys for Ultra-High Temperature Applications—Investigated with Neutron Scattering
Lukas Karge 1 , R. Gilles 1 , D. Mukherji 2 , P. Strunz 3 , P. Beran 3 , J. Roesler 2
1 Heinz Maier-Leibnitz Zentrum, Technichal University Munich, Garching Germany, 2 Institut für Werkstoffe, Technical University Braunschweig, Braunschweig Germany, 3 , Nuclear Physics Institute of the CAS, Rez Czech Republic
Show AbstractThere is a need to supplement Ni-base superalloys in future gas turbines for gas entry temperatures > 1500 °C to improve their efficiency. Co-Re alloys are a promising candidate, since they have the required high melting point as well as the required strength. Measurements by means of small-angle neutron scattering (SANS) and neutron diffraction (ND) were an important part of their development in the past several years [1,2]. These methods allow the investigation of the complex interplay between the different phases that are present in nano- and mesoscopic scale in-situ at high temperatures (up to 1500 °C). Especially with SANS, it was possible to observe the size distribution of fine Tantalum mono-carbide precipitates (<30 nm) and their evolution within the matrix of a Co-Re-Cr-Ta-C alloy [3]. In addition, ND shows that the Co-Re alloy matrix undergoes an allotropic transformation hcp → fcc at temperatures > 1200 °C, which is similar to the behavior of pure Co [4].
Alloys a Ta content of 1.2 at% and varying C/Ta ratios from 0.5-1 were studied in order to investigate the TaC phase stability in detail. Currently, the influence of different heat treatments on the TaC precipitate is under investigation. In-situ SANS and microscopic studies show that precipitates coarsen but remain small (< 80 nm) at temperatures up to 1200 °C.
In this contribution, the focus is on the influence of the C/Ta ratio on size, volume fraction and high temperature stability of the fine TaC, measured by means of in-situ SANS and ND which both provide real bulk information of the alloy. It is shown that the size distribution and the volume fraction strongly depend on the C/Ta ratio, and the coarsening kinetics of fine TaC (< 100 nm) is determined at temperatures up to T = 1500 °C. In addition, the strong influence of Co-Re matrix transformation hcp ↔ fcc on TaC precipitate stability is discussed.
References
[1] D. Mukherji, R. Gilles, L. Karge, P. Strunz, P. Beran, H. Eckerlebe, A. Stark, L. Szentmiklosi, Z. Mácsik, G. Schumacher, I. Zizak, M. Hofmann, M. Hoelzel and J. Rösler, J. Appl. Cryst. 47 (2014) 1417-1430.
[2] D. Mukherji, J. Rösler, J. Wehrs, H. Eckerlebe and R. Gilles, Adv. Mater. Res. 1 (2012) 205-219.
[3] R. Gilles, D. Mukherji, L. Karge, P. Strunz, P. Beran, B. Barbier, A. Kriele, M. Hofmann, H. Eckerlebe, J. Rösler, J. Appl. Cryst. 49 (2016) 1253–1265.
[4] P. Beran, D. Mukherji, P. Strunz, R. Gilles, M. Hofmann, L. Karge, O. Dolotko, J. Rösler. Metals and materials International 22 (2016) 562-571.
12:45 PM - NM9.9.05
High Pressure Phase Stability of Transition Metal High-Entropy Alloys
Cameron Tracy 1 , Sulgiye Park 1 , Dylan Rittman 1 , Maik Lang 2 , Rodney Ewing 1 , Wendy Mao 1
1 Department of Geological Sciences, Stanford University, Stanford, California, United States, 2 Department of Nuclear Engineering, University of Tennessee, Knoxville, Tennessee, United States
Show AbstractHigh-entropy alloys, typically defined as near-equiatomic solid solutions of five or more components, possess many properties favorable for a wide range of applications. However, their phase space is constrained, with the vast majority of these alloys exhibiting only face-centered cubic (fcc) or body-centered cubic (bcc) structures. Their phase behavior under extreme conditions, however, is largely unexplored. Using diamond anvil cell and x-ray diffraction techniques, we report the results of a study of the structural stability of the prototypical transition metal, fcc, high-entropy alloy CrMnFeCoNi at pressures of up to 55 GPa. The compression and phase behavior of this material are explained in terms of the effects of pressure on the magnetism of the constituent elements and its role in phase stabilization.
NM9.10: Mechancial Properties
Session Chairs
Thursday PM, April 20, 2017
PCC West, 100 Level, Room 102 C
2:45 PM - NM9.10.01
Toward the Design of Tribocorrosion Resistant Aluminum Alloys
Hesham Mraied 1 , Wenjun Cai 1
1 , University of South Florida, Tampa, Florida, United States
Show AbstractThe increasing demand for materials suitable for complex service conditions requires the design of new engineering materials resistant to both wear damage and corrosion degradation. Tribocorrosion, material degradation caused by the combined effects of wear, corrosion, and their synergy, is most prominent for passive metals such as aluminum and its alloys, which spontaneously form a passive film when in contact with oxygen or water. When mechanical wear takes place during corrosion, the passive film can be locally destroyed, with the ensuing depassivation leading to rapid localized corrosion and early component failure. In this work, the effects of Mn alloying on the tribocorrosion behavior of Al-Mn supersaturated solid solutions were systematically investigated in 0.6 M NaCl aqueous solution. Mn was found to be highly effective in improving the wear, corrosion, and tribocorrosion resistance of Al. Higher Mn concentration improves the protectiveness of passive film, hardness, and repassivation kinetics of the alloy.
3:00 PM - NM9.10.02
Advanced Mechanical Properties of Powder Metallurgy Titanium with a High Concentration of Oxygen and Nitrogen
Jianghua Shen 1 , Biao Chen 1 , Xiaoxin Ye 1 , Hisashi Imai 1 , Junko Umeda 1 , Katsuyoshi Kondoh 1
1 Composite Materials Processing, Osaka University, Ibaraki, Osaka University, Japan
Show AbstractOxygen and nitrogen are highly effective in strengthening α-Ti through interstitial solid solution. However, the strong strengthening effect always comes with a substantial loss of the ductility. Therefore, the amount of oxygen and nitrogen is limited in Ti and its alloys for industrial applications. In this study, the powder metallurgy (PM) technique was used to fabricate advanced Ti materials with relatively high contents of oxygen and nitrogen. The microstructures of the Ti materials with different concentrations of oxygen and nitrogen were characterized by electron backscattered diffraction (EBSD) affiliated to a scanning electron microscopy (SEM), while the distribution of oxygen and nitrogen was examined using an electron probe micro-analyzer (EPMA). The results show that the oxygen and nitrogen are present in solid solution, and with increasing their concentration, the strength of the materials increases dramatically with a merely reduced elongation-to-failure.
3:15 PM - NM9.10.04
Effect of Rolling Temperature on Microstructure and Tensile Properties of Nanocrystalline/Microcrystalline 304 Stainless Steel
Pei La 1
1 , Lanzhou University of Technology, Lanzhou China
Show AbstractEffect of rolling temperature on microstructure and tensile properties of nanocrystalline/microcrystalline 304 stainless steel prepared by aluminothermic reaction method was investigated in this paper. The results showed when the steel rolled at 1273K with 40% thickness reduction, most nanocrystalline austenite disappeared and grew up to be sub-microcrystalline phase; when the steel rolled at 1273K and 1073K with 80% thickness reduction, nanocrystalline austenite fully disappeared; when the steel rolled at 973K with 70% thickness reduction after rolling at 1273K with 40% thickness reduction, sub-microcrystalline austenite grains were crushed and nanocrystalline austenite merged together to grow up; when the steel rolled at 873K with 70% thickness reduction after rolling at 1273K with 40% thickness reduction, all of the sub-microcrystalline austenite grains were crushed to smaller grains. The steel strength and ductility were much improved after rolling compared with the original cast steel. When the steel rolled at 1273K with 80% thickness reduction, the steel had the maximum elongation value but the lowest tensile and yield strength; when the steel rolled at 1073K with 80% thickness reduction, the steel had the maximum tensile strength but the smallest elongation; when the steel rolled at 873K and 973K with 70% thickness reduction after rolling at 1273K with 40% thickness reduction, the steel had a good combination of strength and ductility. However, when steel rolled at 873K, the yield strength was the highest in all rolling conditions, the strength and elongation were 965/837 MPa and 18.8%, respectively, the combination of strength and elongation were the optimum value of the test steels.
3:30 PM - NM9.10.05
Microstructure and Mechanical Behavior of a Fe-15Mn Steel under Static and Dynamic Conditions
Xiaoxue Chen 1 , Laszlo Kecskes 2 , Qiuming Wei 1
1 Department of Mechanical Engineering and Engineering Science, University of North Carolina at Charlotte, Charlotte, North Carolina, United States, 2 , US Army Research Laboratory, Aberdeen, Maryland, United States
Show AbstractThe microstructure and mechanical behavior of a Fe-15Mn steel with addition of aluminum, silicon, chromium and nickel have been investigated. It demonstrates remarkable work hardening combined with high toughness and ductility at the expense of density. The strain hardening mechanism under tension, quasi-static and dynamic compression was analyzed along normal (ND), rolling (RD) and transverse directions (TD). This alloy shows isotropic behavior under both tensile and compressive loads. Under tensile load, a constant high strain hardening rate accompanied by high strength and high ductility have been achieved (i.e. yield strength: ~600 MPa, ultimate tensile strength: ~1600 MPa, elongation to fracture: ~50%, strain hardening exponent: ~0.35, pull rate: 0.001/s pull rate). Furthermore, the dimple structure was observed from tensile fracture interface. On the other hand, the quasi-static compression test was conducted with the strain rate of ~0.001/s and the flow strength was determined as ~600 MPa. The dynamic mechanical properties were studied using a Split-Hopkinson pressure bar at room temperature with strain rate ~3500/s and the flow strength was approximated at 800MPa. Based on these results, supplemented by X-ray diffraction and microscopy techniques, a general overview of the hardening behavior will be depicted.
3:45 PM - NM9.10.06
Electrochemical Metal Identification Tool for Light Metal Sorting and Recycling
Jessy Rivest 1 , Divyaraj Desai 1
1 , PARC, A Xerox Company, Palo Alto, California, United States
Show AbstractAs vehicles become increasingly lightweighted to improve fuel economy, there will be greater need for recycling these alloys. Recycling the alloys will save energy (re-melting is far less energy-intensive than primary smelting) while lowering the cost of lightweight alloys. For high-value recycling, it is imperative to sort accurately to maintain the specific properties the material was alloyed to demonstrate. The state-of-the-art sorting methods (XRF) is expensive and has a fundamentally low signal-to-noise ratio for light elements, necessitating integration times of more than a minute. Long measurement times and high costs limit the economic incentive for recycling.
We present a fast, accurate, and inexpensive alloy detection method based on a simple electrochemical mechanism.
4:30 PM - NM9.10.07
Low Temperature Relaxation Mode in Bulk Metallic Glasses
Robert Maass 1 , Stefan Kuechemann 1
1 , University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Show AbstractThe analysis of relaxation mechanisms has played an essential role in the understanding of glasses as they reveal fundamental structural differences to crystals. In general, glassy systems exhibit two relaxations modes: the primary α- and the secondary β-process. Primary excitations near the glass transition temperature, Tg, are associated with large cooperative atomic mobility leading to irreversible viscous flow. The secondary β-relaxation process below Tg is understood as a cooperative rearrangement, but it is energetically reversible and reflects structural transitions on a much smaller length scale. Here we reveal the existence of a third structural relaxation mechanism in metallic glasses, which we observe in a Zr-based metallic glass at around 170 K. This low temperature relaxation is very akin to the long known γ-relaxation in amorphous polymers, where it for example has been reported in co-blockpolymers, epoxy resins, and substituted polystyrenes. Contrary to the previously known relaxation mechanism, this irreversible, low energy excitation causes a significant macroscopic rejuvenation, which we assign to non-affine atomic rearrangements in the matrix that are driven by thermal stress during cooling.
4:45 PM - NM9.10.08
Field Induced Martensitic Phase Transition in Disordered Ni45Mn44Sn9In2 Heusler Alloy
Tanmay Chabri 1 , Venimadhav Adyam 1 , Tapan Nath 1
1 , Indian Institute of Technology Kharagpur, Kharagpur India
Show AbstractMaterials with a coupled magneto-structural first-order phase transition may display different kinds of interesting properties due to the presence of the latent heat of the structural transformation. Metastable states are formed due to the first-order nature of the transition and the fascinating dynamics results from the competition between thermal and magnetic energies. The strong coupling between the magnetism and structure in these kinds of materials results an entropy change, which is the main reason to use these materials as magnetocaloric materials, when magnetic field is applied. The ferromagnetic shape memory alloys (FSMAs) undergo a first-order structural transition from a parent austenitic phase (AP) to a martensitic phase (MP) on cooling, which results a sharp change of magnetization due to different ferromagnetic interactions in both phases. The characteristic temperatures in FSMAs are the martensitic start temperature (MS), martensitic finish temperature (Mf), austenitic start temperature (AS) and austenitic finish temperature (Af). The martensitic transition (MT) can be tuned by application of magnetic field. The driving force for the field induced transformation is Zeeman energy EZeeman = μ0△M H, where H is the strength of applied field and △M is the magnetization difference between the AP and MP. Many efforts have been devoted to increase the △M by enhancing the magnetization of AP while reducing the field for driving the MT.
The temperature dependence of magnetization of Ni45Mn44Sn9In2, M(T), upon cooling and heating (FCC, FCW) is measured at magnetic fields of 500 Oe and 1 T, respectively. It is clearly seen that both the direct MT temperature [TAM=(MS+MF)/2] and the reverse MT temperature [TMA=(AS+AF)/2] decrease by -2 K as the magnetic field changes from 500 Oe to 1 T, thus arresting the ferromagnetic AP to the lower temperature due to application of magnetic field. The magnitude of thermal hysteresis gradually increases as the field is raised from 500 Oe to 1 T magnetic field.
5:00 PM - NM9.10.09
Linking Structure to Fragility in Bulk Metallic Glass-Forming Liquids—Understanding the Structural and Dynamic Transitions in a Deeply Undercooled Levitated Metallic Droplet
Shuai Wei 1 , Moritz Stolpe 2 , Oliver Gross 2 , Zach Evenson 3 , Jamie Kruzic 5 , Isabella Gallino 2 , William Hembree 2 , Isabell Jonas 4 , Jozef Bednarcik 6 , Andreas Meyer 4 , Ralf Busch 2
1 , Arizona State University, Tempe, Arizona, United States, 2 , Saarland University, Saarbruecken Germany, 3 , Technische Universität München, Munich Germany, 5 , Oregon State University, Corvallis, Oregon, United States, 4 , German Aerospace Center (DLR), Cologne Germany, 6 , DESY, Hamburg Germany
Show AbstractUsing in-situ synchrotron X-ray scattering, we show that the structural evolution of various bulk metallic glass-forming liquids can be quantitatively connected to their viscosity behavior in the supercooled liquid near Tg. The structural signature of fragility is identified as the temperature dependence of local dilatation on distinct key atomic length scales. A more fragile behavior results from a more pronounced thermally induced dilatation of the structure on a length scale of about 3 to 4 atomic diameters, coupled with shallower temperature dependence of structural changes in the nearest neighbor environment. These findings shed light on the structural origin of viscous slowdown during undercooling of bulk metallic glass-forming liquids. The quantitative structure-fragility relation can be employed for the in-situ structural analysis for a Zr-based bulk metallic glassforming liquid studied using high-energy synchrotron x-ray radiation combined with electrostatic levitation (ESL). The data, spanning over a wide temperature range from above the liquidus temperature down to the glass transition without interference of crystallization, indicate a liquid-liquid transition(LLT) in the deeply undercooled state at T/Tg ∼1.2 which manifests as a maximum in the heat capacity and an abrupt shift in the first peak position of the total structure factor in the absence of a pronounced density change. Analysis of the corresponding real-space data shows that the LLT involves changes in short- and medium-range order. From the structural changes, the fragility changes can be derived, suggesting a fragile-strong transition in the liquid in agreement with experimental viscosity data.
5:15 PM - NM9.10.10
Characterization of Fiber Laser Welded TC4/SS 304 Joints Using Cu Interlayer
Seyed Reza Elmi Hosseini 1 , Zhuguo Li 1 , Yuan Chen 1 , Da Shu 1
1 Shanghai Key Laboratory of Materials Laser Processing and Modification, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai China
Show AbstractThe fiber laser welding of Ti64 alloy to AISI 304 stainless steel by a pure Cu interlayer was developed. The microstructure and fracture characteristic of the joints were analyzed by OM, SEM, EDS and X-ray diffraction. The accepted joints could be obtained under the optimized laser power. The best value for cross-weld tensile strength of the joints was up to 300 MPa, recovering 45% of titanium alloy strength. The intermetallic compounds were observed in the Ti/weld interface, and the joints all fractured at the Ti/Cu interfaces. The maximum strength observed at the laser power of 3 kW, as with increasing the laser power, the tensile first increased and then decreased. Furthermore, the strong links between the laser power and the intermetallic formation and then with joining mechanism were found and discussed by the experimental results.