Symposium Organizers
Amit Misra Los Alamos National Laboratory
John P. Sullivan Sandia National Laboratories
Hanchen Huang Rensselaer Polytechnic Institute
Ke Lu Chinese Academy of Sciences
Syed Asif Hysitron, Inc.
Z1: Nanoscale Films
Session Chairs
Robert Cammarata
Amit Misra
Tuesday PM, April 18, 2006
Room 2003 (Moscone West)
9:00 AM - **Z1.1
Hierarchical Modeling of Grain Boundary Diffusion and Dislocation Mechanisms in Thin Films and Nanocrystalline Materials.
Huajian Gao 1 , Markus Buehler 2 , Alexander Hartmaier 1 , Shuyu Wei 3 1 , Ji Chen 3 1 , Ke Lu 3
1 -, Max Planck Institute for Metals Research, Stuttgart Germany, 2 Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 3 Shenyang National Laboratory for Materials Science, Chinese Academy of Sciences, Institute of Metal Research, Shenyang, -, China
Show AbstractIn studies of diffusional creep in polycrystalline thin films deposited on substrates, a new class of defects called the grain boundary diffusion wedge has been discovered. The diffusion wedges can be formed either by mass transport between free surfaces and grain boundaries or by absorption of dislocations into grain boundaries. In thin films on substrates, the diffusion wedge induces crack-like singular stress field and as a result, dislocations moving on glide planes parallel to the substrate can be nucleated at the root of the grain boundary, which is unexpected because the biaxial stress field of a thin film does not create a resolved shear stress parallel to the substrate to cause parallel glide motion. This has been verified by recent in-situ TEM experiments conducted at the Max Planck Institute. In nanocrystalline materials, diffusion wedges can lead to brittle crack propagation as the plastic deformation mechanisms are exhausted. In order to fully understand this phenomenon, we have developed a hierarchical modeling scheme in which semi-empirical interatomic EAM potentials derived from quantum mechanical calculations are used in large-scale classical molecular dynamics simulations to clarify the atomic mechanisms of grain boundary diffusion and the associated dislocation mechanisms. The results of molecular dynamics simulations are then fed into a mesoscopic discrete dislocation model to simulate the complex interaction mechanisms between dislocations and grain boundaries at larger length and time scales. The results of these studies compare favorably with relevant experimental data, which has led, for example, to a deformation mechanism map for thin film plasticity.
9:30 AM - Z1.2
Linking the Mechanical Behavior and Deformation Microstructure of Nanoporous Gold Thin Films
Ye Sun 1 , T. John Balk 1
1 Chemical and Materials Engineering, University of Kentucky, Lexington, Kentucky, United States
Show AbstractWhile the chemical properties of nanoporous gold (NPG) have been investigated for years, its mechanical behavior has received relatively little attention. Given its high surface-to-volume ratio and noble metal chemistry, NPG holds potential for sensor and catalysis applications, but its mechanical properties must be better understood. Recently, other researchers have studied the compressive response of NPG during indentation experiments and have found elevated strength levels that greatly exceed that of bulk gold. Nonetheless, an understanding of the deformation mechanisms at the microstructural level is still needed.This presentation will focus on stress evolution in NPG during dealloying from gold-silver precursor films and during subsequent thermal cycling. The measured mechanical behavior of these NPG films will be compared to in-situ transmission electron microscopy observations of the deformation microstructure that develops within NPG during low-temperature thermal cycling and during tensile experiments. NPG films with thicknesses of 100 nm or less were deposited on single-crystal silicon substrates for thermal cycling, or on polyimide substrates for tensile testing.The observations obtained from these experiments will help assess the fundamental deformation behavior of NPG, which has been found to be either brittle or ductile, depending on pore morphology. This study will also shed light on the role of dislocations in the plastic deformation of highly confined metal volumes.
9:45 AM - Z1.3
Mechanical Properties and Failure Mechanisms of Free-Standing Nanoporous Gold
Dongyun Lee 1 , Jeffrey Kysar 1 , Xi Chen 2
1 Mechanical Engineering, Columbia University, New York, New York, United States, 2 Civil Engineering and Engineering Mechanics, Columbia University, New York, New York, United States
Show AbstractNanoporous materials have many potential applications such as for catalysis, sensing of chemical and biological species, and as a component of actuators. In this work, free-standing nanoporous gold is synthesized from “white gold” leaf (50% Au and 50% Ag by weight) and also from the simultaneous deposition of Au and Ag by magnetron sputtering. Both types of films are initially deposited onto silicon substrate and standard lithographic techniques are employed to fabricate mechanical testing specimens of a dog-bone shape. The silicon substrate under the gauge section of the specimens is then etched away via reactive ion etching (RIE) in order to obtain free-standing specimens which are suspended by two anchors of the original silicon substrate which are not removed. The gauge length of each specimen is 7 micrometers in length and the cross-sectional dimensions of the gauge length are in the range of 100 to 150 nm by 100 to 500 nm. The specimen is then dealloyed using nitric acid, which dissolved the silver and leaves random open-pored media of gold. The sizes of the ligaments and the voids are of the order of tens of nanometers and can be tuned with processing parameters. In this study, the mechanical properties of the nanoporous Au obtained by both synthesis methods are contrasted. In addition, the dealloying parameters for each of the two synthesis methods are systematically varied in order to be able to determine the effect on the mechanical properties of changing the sizes of the voids and ligaments. The mechanical properties of the nanoporous gold are probed by deflecting the gauge section of the free-standing specimen with a nanoindenter. Results demonstrate the nanoporous gold may deform elastically up to a stress of approximately 400 MPa, after which failure occurs in what is apparently a brittle manner, although it may be accompanied by plastic deformation in some of the ligaments.
10:00 AM - **Z1.4
The Mechanisms of Small-scale Plasticity as Revealed by in-situ Nanoindentation.
Andrew Minor 1 , Zhiwei Shan 1 , Eric Stach 2 , Miao Jin 3 , J.W. Morris, Jr. 3 , Syed Asif 4 , Oden Warren 4
1 NCEM, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 2 School of Materials Engineering, Purdue University, West Lafayette, Indiana, United States, 3 Department of Materials Science and Engineering, University of California, Berkeley, Berkeley, California, United States, 4 , Hysitron, Inc., Minneapolis, Minnesota, United States
Show AbstractThe experimental technique of in situ nanoindentation in a TEM allows for real time imaging of the initial stages of plasticity in materials, including the observation of dislocation nucleation and phase transformation events. Over the past 5 years, this technique has provided significant insight into the mechanical behavior of nanocrystalline materials and nano-scale volumes. This talk will highlight the most important findings regarding the mechanical behavior of metals and ceramics that were revealed with this technique. The findings will include observations of (1) dislocation nucleation events in Al thin films, (2) grain boundary movement in sub-micron and nanocrystalline Al thin films, (3) indentation behavior of ceramic nanoparticles, and (4) dislocation plasticity and phase transformation behavior in silicon. In all cases the in situ observations and measurements will be compared to ex situ nanoindentation tests and discussed in terms of the mechanisms that determine strength in nanoscale volumes.
10:30 AM - Z1.5
Thermodynamics and Mechanics of Solid Surfaces Applied to Modeling of Nanoscale Materials and Devices
Robert Cammarata 1 2
1 Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland, United States, 2 Mechanical Engineering, Johns Hopkins University, Baltimore, Maryland, United States
Show AbstractA major characteristic of nanoscale materials and devices is the large surface to volume ratio, and this ratio can have a large affect on the behavior of the materials. A complete thermodynamic understanding of solid surfaces in nanoscale materials is therefore important when attempting to model and understand the mechanics of these systems. Gibbs developed a general and rigorous treatment of fluid interfaces that has become the standard treatment of surface thermodynamics. However, in the case of interfaces involving solids, Gibbs recognized that there were certain difficulties that required his analysis to be restricted to single component systems under special constraints (and was formulated without any reference to lattice sites in a crystal). However, his unrestricted approach to fluid systems has often been applied to solids without justification and has sometimes resulted in a confusing and often misleading description of solid surfaces. For example, the concept of chemical potential, which is well-defined for fluid systems, becomes problematic for solid surfaces (even under hydrostatic stress), leading to difficulties in defining quantities such as surface energy that are central to the mechanics of surfaces and nanoscale materials. It will be shown that many of these issues can be addressed by reformulating the thermodynamics of surfaces in terms of “surface availability" that is consistent with the standard thermodynamics of fluid surfaces but allows for a complete and rigorous description of interfaces involving crystals. Applications of this approach will be given to certain model nanoscale systems that show the errors introduced by using the methodology of conventional fluid thermodynamics and how the new approach gives an unambiguous and proper description of the mechanics of small solids.
11:15 AM - Z1.6
Understanding the Mechanical Properties of Nanoporous Au
Juergen Biener 1 , Luis Zepeda-Ruiz 1 , Andrea Hodge 1 , Joel Hayes 1 , Peter Bythrow 1 , Yinmin Wang 1 , Farid Abraham 1 , Alex Hamza 1
1 Nanoscale Synthesis and Characterization Laboratory, Lawrence Livermore National Laboratory, Livermore, California, United States
Show AbstractRecent mechanical studies on nanoporous gold (np-Au) have revealed that the yield strength of this material is approximately one order of magnitude higher than predicted by scaling equations developed for open-cell foams. The higher-than-expected yield strength seems to be linked to the nanoscale morphology of np-Au which can be described as an open sponge-like network of interconnecting ligaments on the nanometer length scale. However, even though np-Au is a prototype nanoporous metal, the mechanical properties are not well understood yet. Here, we compare experimental results with molecular dynamics simulations to elucidate the nature of the high yield strength of nanoporous gold. This work was performed under the auspices of the U.S. Department of Energy by University of California, Lawrence Livermore National Laboratory under contract of No.W-7405-Eng-48.
11:30 AM - **Z1.7
Mechanisms of Slip Transmission in Nanolayered fcc/bcc Composites.
Richard Hoagland 1 , Srinivasan Srivilliputhur 1 , Amit Misra 1 , Michael Demkowicz 1
1 MST-08, Los Alamos National Laboratory, Santa Fe, New Mexico, United States
Show AbstractThe theoretical strength is nearly achieved in layered metallic composites when the layer thicknesses are reduced to about 5 nm or less. In cases where the constituents have the same phase and are coherent or even semicoherent, high strengths are attributable to coherency stresses. However, coherency stresses cannot be important in incoherent systems when the phases of the components are dissimilar. Nevertheless, composites that contain incoherent interfaces also achieve very high strength levels. We describe the results of atomistic simulations that reveal some of the features of fcc/bcc composite materials that are important to strength. One feature of considerable importance is the in-plane shear strength. When the interfacial shear strength is substantially lower than typical theoretical strength estimates, glide dislocations within either component may be attracted to interfaces and, on entering, dissociate via core spreading. Once this occurs, continued transmission of slip, in the absence of thermal activation, becomes very difficult. However, we find that some unusual mechanisms are available to such systems that can make slip transmission easier. These mechanisms involve cooperative interaction between small groups of dislocations. We will also reflect on the relations between the properties of the system that are important to strength.This research supported by OBES of the U. S. Dept. of Energy.
12:00 PM - **Z1.8
Fatigue of Thin Metal Films at the Submicron and Nano Scale.
Dong Wang 1 , Cynthia Volkert 1 , Sophie Eve 1 , Norbert Huber 1 , Guangping Zhang 2 , Oliver Kraft 1 3
1 Institut fuer Materialforschung II, Forschungszentrum Karlsruhe, Karlsruhe Germany, 2 Institute of Metal Research, Chinese Academy of Sciences, Shenyang China, 3 IZBS, Universitaet Karlsruhe, Karlsruhe Germany
Show AbstractOne current trend in microelectronics and MEMS/NEMS is to develop devices based on plastic substrates. For such thin film devices, cyclic mechanical or thermal loading conditions with typical strain ranges up to 1% may lead to fatigue damage formation such as cracking, surface roughening and delamination. It is well known that fatigue of metallic materials at the macro-scale is often related to the formation of long-range dislocation structures, which lead to surface roughening of a component or specimen, and subsequent crack formation starting from the roughened surface. In the light of this damage evolution, it is not obvious how materials fatigue when dimensions are reduced to the sub-micron and nano regime, as in thin films or nanostructures with grain sizes of similar magnitude. On the one hand, the ratio of surface to volume is strongly increased, which may promote crack formation, while on the other hand, the available material volume is reduced preventing long range dislocation ordering.In order to elucidate these mechanisms, we have developed a number of methods to characterize the fatigue behavior of thin metal films. These methods include uniaxial and equi-biaxial loading of Cu and Au films on polymer substrates. In both tests, the substrate material is expected to deform elastically while the film may undergo plastic deformation in both tension and compression. A study on the effect of length scale, both film thickness and grain size, on fatigue-induced damage morphology in Cu films revealed that the amount of surface roughening decreases with decreasing film thickness and that long range dislocation structures were only found in films and grains larger than 1.0 µm. Furthermore, the damage morphology changes from intra- to inter-granular cracking with decreasing dimensions. In addition other changes in surface damage are observed which suggest that diffusion is active during fatigue of the thinnest films. Currently, a more detailed investigation of the influence of film thickness in the regime of 50 to 3000 nm on the fatigue mechanisms is being performed.
12:30 PM - Z1.9
Ab initio Study of Surface Stresses of Charged Au films.
Yoshitaka Umeno 1 2 , Joerg Weissmueller 3 4 , Ferdinand Evers 3 , Martina Nothacker 3 , Christian Elsaesser 5 , Bernd Meyer 6 , Peter Gumbsch 2 5
1 Department of Mechanical Engineering and Science, Kyoto University, Kyoto Japan, 2 Institut fuer Zuverlaessigkeit von Bauteilen und Systemen, Universitaet Karlsruhe, Karlsruhe Germany, 3 Institut fuer Nanotechnologie, Forschungszentrum Karlsruhe GmbH, Karlsruhe Germany, 4 Technische Physik, Universitaet des Saarlandes, Saarbruecken Germany, 5 Physikalische Werkstoffmodellierung, Fraunhofer Institut fuer Werkstoffmechanik IWM, Freiburg Germany, 6 Lehrstuhl fuer Theoretische Chemie, Ruhr-Universitaet Bochum, Bochum Germany
Show Abstract12:45 PM - Z1.10
Atomic-Scale Analysis Of Sress-Induced Nanocrystalline Domain Formation In Ultra-Thin Metallic Films And Characterization Of The Resulting Structure And Properties.
M. Rauf Gungor 1 , Dimitrios Maroudas 1
1 Department of Chemical Engineering, University of Massachusetts, Amherst, Massachusetts, United States
Show AbstractReducing the grain size of metallic thin films can have a dramatic influence on material properties such as ductility, hardness, electrical conductivity, and mechanical strength. Furthermore, reduction of the grain size down to a few nanometers can lead to “extreme” material properties with a potentially wide range of nanotechnological applications. Fundamental understanding based on detailed atomic-scale investigation of nanocrystalline domain formation mechanisms and characterization of the resulting material structure and properties is required to assess the application potential of such nanostructured thin-film materials. In this presentation, we report results of a systematic computational analysis of strain relaxation mechanisms due to high levels of applied biaxial tensile strain in ultra-thin Cu films with the film plane oriented normal to the [111] crystallographic direction. The major strain relaxation mechanism observed leads to transformation of an initially single-crystalline structure into a polycrystalline structure with an average grain size of 1.5 nm. The analysis is based on isothermal-isostrain molecular-dynamics simulations using an embedded-atom-method parameterization for Cu and slab supercells with millions of atoms. Under application of high biaxial strain (> 8%) to a free-standing ultra-thin Cu film, a strain relaxation mechanism is activated that leads to formation of a uniformly distributed population of dislocations and point defects. Under such conditions, nanometer-scale domains of fcc crystalline material are formed leading to the transformation of the initially single-crystalline metallic film to a nanocrystalline structure with nanometer-sized grains. We analyze the atomistic mechanisms of strain-induced nanocrystalline domain formation, mainly due to rearrangement of strain-induced defect populations to form low-angle grain boundaries. In addition, we analyze the effects of the loading rate on the mechanism of nanocrystalline phase formation by enabling ductile growth of a centrally located cylindrical void as a competing strain relaxation mechanism, which is activated at a slower loading rate and dominates at lower strain levels. Finally, by relaxing and subsequently reloading biaxially the obtained nanocrystalline structure, we characterize the nanocrystalline film in terms of its ductility, elastic properties, and fracture toughness in comparison with the single-crystalline material. We find that the elastic modulus of the nanocrystalline thin film is several times higher than that of the single-crystalline film.
Z2: Nanoscale Materials
Session Chairs
Richard Hoagland
Scott Mao
Tuesday PM, April 18, 2006
Room 2003 (Moscone West)
2:30 PM - **Z2.1
Deformation Mechanism in Nanocrystalline fcc metals: Experiments and Simulations.
Helena Van Swygenhoven 1 , Stefan Brandstetter 1 , Zeljka Budrovic 1 , Steven Van Petegem 1 , Peter Derlet 1
1 , Paul Scherrer Institution, Villigen PSI Switzerland
Show AbstractBy combining in-situ x-ray diffraction during mechanical testing, TEM analysis and large scale atomistic computer simulations synergies are created providing a different view on the outcome of the conventional mechanical testing. In-situ profile analysis allows following the XRD footprints of the microstructure during loading and TEM analysis reveals the microstructure before an after load. Atomistic simulations provides, when put in their proper context taking into account possible artefacts from the short time/high stress character of simulations and the use of empirical potentials, invaluable details on deformation mechanism and how these are influenced by external parameters such as temperature. In this talk we report on in-situ and ex-situ load-unload experiments performed as well in tension as in compression, stress relaxations, strain rate jump tests and creep tests all performed at room temperature and some also at lower temperatures. Two materials are compared, a HPT Ni sample with mean grain size of 300nm and an electrodeposited Ni sample with a mean grain size of 30nm. We also present an overview of the suggestions of atomistic simulations concerning dislocation nucleation, propagation and absorption with a particular emphasis on the aspects in terms of thermal activation. Results such as the reversibility of the peak broadening at room temperature which is lost at lower temperatures, the low activation volume at room temperature and its increase with decreasing temperature are discussed in terms of the details of dislocation nucleation and propagation as suggested by simulations.
3:00 PM - **Z2.2
Multiscale Approaches On Modeling Grain-Boundaries In Nanocrystalline Metals.
Vesselin Yamakov 1
1 , National Institute of Aerospace, Hampton, Virginia, United States
Show AbstractIt is already well understood that the mechanical properties of nanocrystalline metals are strongly related to grain-boundary (GB) mediated processes, such as GB sliding, GB diffusion, grain growth, intergranular fracture, etc. Because of this, the accurate simulation of GBs' behavior is becoming a key factor for representing the mechanical properties of nanocrystalline metals. Two mesoscale models for representing GBs in a polycrystalline metal will be discussed. Both models use molecular-dynamics simulation to parameterize and validate their behavior. The first model is based on Pan and Cock's (Pan J, Cocks ACF. 1993, Comp Mater Sci. 1, 95.) technique for evolving a GB network in a polycrystal under deformation and during grain growth. The model is applied for simulating dynamic grain growth during large-strain GB diffusion assisted plastic deformation in nanocrystalline metals at elevated temperatures. The second model is based on Tvergaard and Hutchinson (Tvergaard V, Hutchinson JW, 1992, J. Mech. Phys. Solids 40, 1377) cohesive-zone model. Cohesive zone models (CZMs) approximate traction-displacement relationships along an interface and are frequently used in conjunction with the finite element method (FEM) to study fracture in a wide variety of materials. In the present work, it is shown that CZM can equally well be used to represent GB sliding during deformation. At low temperature, and in the absence of accommodation mechanisms, this GB sliding can cause substantial inhomogeneity in the stress-strain field in the loaded specimen, which can cause material failure through the mechanism of intergranular fracture.
3:30 PM - Z2.3
Structure and Mechanical Properties of Kurdjumov-Sachs Interfaces with Low Shear Resistance.
Michael Demkowicz 1 , Richard Hoagland 1 , Srinivasan Srivilliputhur 1 , Amit Misra 1
1 Michael Demkowicz, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show Abstract3:45 PM - Z2.4
Atomistic Analysis of Small-Scale Crystal Plasticity.
R. McEntire 1 2 , Yu-Lin Shen 1
1 Mechanical Engineering, University of New Mexico, Albuquerque, New Mexico, United States, 2 , Sandia National Laboratories, Albuquerque, New Mexico, United States
Show AbstractPlastic deformation and fracture in FCC crystals are studied using three dimensional atomistic simulations. The primary objective is to gain fundamental insight into nano-scale deformation features in thin films and small structures. An initial defect is utilized in the models to trigger dislocation activities in a controlled manner. Attention is devoted to correlating atomistic mechanisms with the overall mechanical response of the material. The slip phenomena are seen to follow the Schmid’s law under uniaxial loading along various crystallographic directions. The creation of slip steps at the sample surfaces is associated with a sudden reduction in stress along the stress-strain curve. The accumulation of plasticity leads to eventual ductile fracture of the crystal. When the material is attached to a flat substrate, plastic yielding is delayed. The material behavior under equi-biaxial loading parallel to the <111> plane is also analyzed.
4:30 PM - **Z2.5
Dislocation Activities and Partial Dislocation Mediated Processes in Nanocrystalline Grains.
Evan Ma 1
1 Materials Sci & Eng, Johns Hopkins University, Baltimore, Maryland, United States
Show AbstractWe discuss the dislocation behavior in plastically deforming metals when the grain sizes are reduced to well below 100 nm. Such grain sizes are often involved in thin films and MEMS materials. We compare the activation parameters of dislocation processes in nanograins with those in conventional metals, and illustrate in particular the various manifestations of partial dislocation mediated processes. For example, we discuss when and why deformation twinning and stacking fault formation come into play during unaxial tensile deformation of nanocrystalline Ni, explain the temperature effects in addition to grain size effects, and provide details regarding the deformation twinning mechanisms in nanograins. Our results not only establish that dislocation activities and partial dislocation mediated processes are clearly activated in nanograins, but also reveal their differences from those in conventional coarse-gained metals. We also discuss the results in comparison with the predictions given by MD simulations and generalized planar fault energy curves, as well as in light of the kinetics involved in the thermally activated dislocation nucleation and propagation. This research is part of an international collaboration effort. This talk will be based on the large number of TEM observations made by Dr. X.L. Wu (Chinese Academy of Science), and the stimulating discussions with Dr. Y.T. Zhu (LANL) and Dr. M.W. Chen (Tohoku Univ.).
5:00 PM - Z2.6
In situ, Quantitative TEM Nanoindentation Tests of Materials.
Zhiwei Shan 1 , Andrew Minor 1 , Syed Asif 2 , Oden Warren 2
1 National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 2 , Hysitron Incorporated, Minneapolis, Minnesota, United States
Show Abstract5:15 PM - Z2.7
High-strength Sputter-deposited Cu Films with Nanoscale Growth Twins.
Xinghang Zhang 1 , Amit Misra 2 , H. Wang 3 , X. Chen 4 , L. Lu 4 , K. Lu 4 , R. Hoagland 2
1 Department of Mechanical Engineering, Texas A&M University, College Station, Texas, United States, 2 Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 3 Department of Electrical Engineering, Texas A&M University, College Station, Texas, United States, 4 Chinese Academy of Sciences, Institute of Metals Research, Shenyang National Laboratory for Materials Science (SYNL), Shenyang China
Show AbstractWe have shown for the first time that nanoscale growth twins, with an average twin spacing of around 5 nm, can be synthesized in Cu using magnetron sputtering technique. Such fine growth twins have been observed in sputtered 330 stainless steel alloys before [1,2]. Sputtered Cu has an average columnar grain size of less than 100 nm. Growth twins located in columnar grains are of {111} type as confirmed by high resolution transmission electron microscopy, with {111} twin interface predominantly parallel to substrate surface. The hardness of twinned Cu reaches 3.5 GPa as determined by nanoindentation technique. Uniaxial tensile tests were performed on 20 micron thick sputtered Cu foils. Average yield strength of 1.1 GPa was observed in these Cu foils with an average true strain of 2%. 1. X. Zhang, A. Misra, et al., Journal of Applied Physics, 97 (2005) 094302.2. X. Zhang, A. Misra, et al., Applied Physics Letters, 84 (2004) 1096.
5:30 PM - Z2.8
Fatigue-Induced Dynamic Coarsening in Nanocrystalline Electrodeposited Ni-Mn MEMS Structures
Brad Boyce 1 , Joseph Michael 1 , Thomas Buchheit 1 , Steven Goods 2
1 , Sandia National Laboratories, Albuquerque, New Mexico, United States, 2 , Sandia National Laboratories, Livermore, California, United States
Show AbstractThe methods used to produce ultra-fine grained and nanocrystalline structures, such as by electrodepostion, may produce microstructures that are susceptible to unusual mechanisms for mechanical failure. In this study, we examine the fatigue-behavior of a nanocrystalline (~80-100 nm) Ni-Mn fatigue structure produced using the LIGA process for metallic microelectromechanical systems (MEMS) fabrication. This material has useful properties for structural applications, including a yield strength >1 GPa, reasonable ductility and resistance to anneal softening. With these properties, the material could be considered for spring-like applications where cyclic fatigue-loading could lead to latent failure. Cross-sections of samples after high-cycle fatigue failure at room temperature, prepared and imaged with a Focused Ion Beam (FIB) tool, showed dramatically coarsened grains that were >10X larger than the parent microstructure. This dynamic coarsening only formed in the immediate vicinity of fatigue-cracks and subsequent crack-propagation appears to be controlled by this much coarser microstructure rather than by the nanocrystalline parent microstructure. Backscatter diffraction revealed that these grains retained the strong {110} electrodeposition texture of the parent microstructure, suggesting that the grains may have grown by an Ostwald process rather than recrystallization. Previous studies of the Ni-Mn microstructure showed similar degrees of coarsening but only after thermal-annealing at ≥600C for 1 hr. This fatigue-induced coarsening behavior of ultrafine grained Ni-Mn is in contrast to the behavior of electrodeposited Ni with coarser 3-5 μm grains where no dynamic coarsening was observed after high-cycle fatigue loading. In spite of the very different mechanisms associated with fatigue failure of these two alloys, their resulting stress-life (S-N) failure envelope was similar when normalized by the ultimate tensile strength.Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under contract DE-AC04-94AL85000.
5:45 PM - Z2.9
Analysis of Strengthening Mechanisms in a Severely-Plastically-Deformed Al-Mg-Si Alloy with Submicron Grain Size.
David Morris 1 , Ivan Gutierrez-Urrutia 1 , Maria Munoz-Morris 1
1 Physical Metallurgy, CENIM,CSIC, Madrid Spain
Show AbstractMethods of severe plastic deformation of ductile metals and alloys offer the possibility of processing engineering materials to very high strength with good ductility. After typical amounts of processing strain, a submicrocrystalline material is obtained, with boundaries of rather low misorientation angles and grains containing a high density of dislocations. In the present study, an Al-Mg-Si alloy was severely plastically deformed by equal channel angular pressing (ECAP) to produce such a material. The material was subsequently annealed for dislocation recovery and grain growth. The strength of materials in various deformed and annealed states is examined and the respective contributions of loosely-arranged dislocations, many grain boundaries, as well as dispersed particles are deduced. It is shown that dislocation strengthening is significant in as-deformed, as well as lightly annealed materials, with grain boundary strengthening providing the major contribution in further annealed materials.
Z3: Poster Session: Nano-materials and Composites
Session Chairs
Wednesday AM, April 19, 2006
Salons 8-15 (Marriott)
9:00 PM - Z3.1
Sample Size Effect on Nanoindentation Mechanical Property Measurements.
Zhi-Hui Xu 1 , Xiaodong Li 1
1 Department of Mechanical Engineering, University of South Carolina, Columbia, South Carolina, United States
Show AbstractNanoindentation has been widely used for measuring the mechanical properties of materials at a small volume. The current method for the analysis of nanoindentation load-penetration depth curve is based on Sneddon’s equation, an elastic solution of indentation on semi-infinite half space. For nanoindentations on tiny structures, such as nanowires, nanobelts, and nanoparticles, the sample size is often comparable to the indent size and the Sneddon’s equation may not be fully valid. In this study, a finite element simulation has been carried out to investigate the sample size effect on the mechanical properties measured by nanoindentation. It is shown that significant errors occur in both hardness and elastic modulus measurements when the sample size is comparable to the indent size. Caution should be exercised in the analysis of nanoindentation curve of tiny structures.
9:00 PM - Z3.10
Transmission Electron Microscopy Study of the Mechanical Behavior of Nanoscale Materials.
Julia Deneen 1 , William Mook 1 , Andrew Minor 2 , William Gerberich 1 , C. Barry Carter 1
1 Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota, United States, 2 Ernest Orlando Lawrence Berkeley National Laboratory, National Center For Electron Microscopy, Berkeley, California, United States
Show AbstractThe mechanical properties of nanoparticles and nanoscale materials are of great scientific interest. The wear properties of nanoscale components of, for example, microelectromechanical systems must be addressed as these devices are scaled down. While indirect studies suggest that nanoscale materials can be harder than their bulk counterparts, the practical difficulties in characterizing their mechanical behavior have traditionally been limited to what can actually be observed. The transmission electron microscope is commonly used to investigate the deformation mechanisms of materials, as it can be used to image dislocation strain fields. In most cases, however, the sample cannot be characterized prior to deformation. This study uses nontraditional methods to investigate the mechanical behavior of nanoscale materials. Using an in-situ nanoindentation sample holder for the TEM, direct observation of nanoparticle fracture is possible by simultaneous compression and imaging. Using this method, preexisting defects and surface layers can be identified and the sample orientation can be determined using diffraction techniques. Ex-situ studies of plan-view thin-film samples are also explored. By imaging the TEM sample and subsequently indenting the sample using traditional nanoindentation methods it is possible to characterize a specific area both before and after deformation. Both in-situ and ex-situ techniques offer new insight into the mechanical behavior of nanoscale materials.
9:00 PM - Z3.11
In-situ Photoemission Electron Microscopy Study of Thermally-induced Martensitic Transformation in CuZnAl Shape Memory Alloy.
Gang Xiong 1 , M Cai 2 , A Joly 1 , Wayne Hess 1 , Kenneth Beck 1 , J Dickinson 2
1 , Pacific Northwest National Laboratory, Richland, Washington, United States, 2 2Department of Physics and Astronomy, Washington State University, Pullman, Washington, United States
Show AbstractPhotoemission electron microscopy, in conjunction with photoemission spectroscopy, reflectivity, and surface roughness measurements, is used to study the thermally-induced martensitic transformation in a CuZnAl shape memory alloy. Real-time phase transformation is observed as a nearly instantaneous change of photoelectron intensity, accompanied by microstructural deformation and displacement due to the shape memory effect. The difference in the photoelectron intensity before and after the phase transformation is attributed to the concomitant change of work function as measured by photoelectron spectroscopy. Photoemission electron microscopy is shown to be a valuable new technique facilitating the study of phase transformations in shape memory alloys, and provides real-time information on microstructural changes and phase-dependent electronic properties.
9:00 PM - Z3.12
In-situ Study on Effects of Annealing Temperature and Mo Interlayer on Stress Relaxation Behaviors of Pure Al Films on Glass Substrates.
Young-Bae Park 1 , Soo-Jung Hwang 2 , Yong-Duk Lee 1 , Ja-Young Jung 1 , Young-Chang Joo 2
1 School of Materials Science and Engineering, Andong National University, Andong Korea (the Republic of), 2 School of Materials Science and Engineering, Seoul National University, Seoul Korea (the Republic of)
Show Abstract9:00 PM - Z3.13
Investigation of the Influence of Grain Size, Texture and Orientation of Freestanding Polycrystalline Gold Films
Liwei Wang 1 , Bart Prorok 1
1 Materials Engineering, Auburn University, Auburn, Alabama, United States
Show AbstractThe Membrane Deflection Experiment (MDE), developed by Espinosa and co-workers [1,2] was employed to perform the wafer-level tensile testing on freestanding thin films of various FCC metals. Gold films with varying thickness of 0.25 to 1.5 µm were deposited by both E-Beam evaporation and sputtering techniques. Process parameter adjustments and annealing were performed to modulate the film microstructure. High-resolution SEM, including electron-backscattered diffraction (EBSD), was employed to provide a crystallographic analysis including grain orientation maps of the studied films. The Young’s modulus of gold deposited by E-Beam evaporation was measured consistently in the range of 53-55 GPa while 68-72 GPa for the sputtered films. Plastic yielding of the e-beam and sputtered films was contrasted due to varying microstructure of each deposition technique, which appears to assert a measure of control on the deformation mechanics. An analysis will be presented on the effects of microstructure and correlated to the obtained orientation maps. Numerical simulations were also conducted to verify the validity of the MDE test results and resulted in a correction factor to increase the accuracy of the test data.[1] Espinosa, H.D., B.C. Prorok, and M. Fischer, Journal of the Mechanics and Physics of Solids, 2003. 51(1): p. 47-67.[2] Espinosa, H.D., B.C. Prorok, and B. Peng, Journal of the Mechanics and Physics of Solids, 2004. 52(3): p. 667-689.
9:00 PM - Z3.16
Effect of Microstructures and Textures on Mechanical Properties in Electrodeposited Ni foils
Yong Bum Park 1 , Nak Hyeon Lim 1
1 Materials Sicence and Metallurgical Engineering, Nanomaterials Research Center, Sunchon National University, Sunchon Korea (the Republic of)
Show AbstractPure Ni electrodeposits with different microstructures and textures were fabricated under different electrodeposition conditions. The evolution of microtextures taking place during annealing was quantitatively investigated by means of the orientation imaging microscopy analysis. In the sample consisting of equiaxed crystallites ranging between 10 and 15 nanometers, the as-deposited texture characterized by a mixture of strong <100>//ND and weak <111>//ND fiber components was transformed into the growth texture with the strong development of the <111>//ND components during annealing above 230oC. In the sample where columnar grains ranging from a few hundreds of nanometers to a few micrometers were formed in the as-deposited state, the <112>//ND grains, a minor component in the initial texture, grew readily to dominate the final texture. The mechanical properties such as hardness and elastic modulus were measured using a nanoindentation test and discussed in terms of the possible effects of the grain morphology and orientation distribution developing in the specimens.
9:00 PM - Z3.17
Cracking and Adhesion at Small Scales: Atomistic and Continuum Studies of Flaw Tolerant Nanostructures.
Markus Buehler 1 , Haimin Yao 2 , Huajian Gao 2
1 Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 , Max Planck Institute for Metals Research, Stuttgart Germany
Show AbstractOnce the characteristic size of materials reaches nanoscale, the mechanical properties may change drastically and classical mechanisms of materials failure cease to hold. In this paper, we focus on joint atomistic-continuum studies of failure and deformation of nanoscale materials. In the first part of the paper, we discuss the size dependence of brittle fracture. We illustrate that if the characteristic dimension of a material is below a critical length scale on the order of several nanometers, the classical Griffith theory of fracture no longer holds. An important consequence of this finding is that materials with nano-substructures become flaw-tolerant, as the stress concentration at crack tips disappears and failure always occurs at the theoretical strength of materials, regardless of defects. Our atomistic simulations complement recent continuum analysis (Gao et al., PNAS, 2003) and reveal a smooth transition between Griffith modes of failure via crack propagation to uniform bond rupture at theoretical strength below a nanometer critical length. This indicates that materials with characteristic features below a critical length scale always achieve their optimal, theoretical strength, independent of the presence of flaws. Our results have important consequences for understanding failure of many small-scale materials. In the second part of this paper, we focus on the size dependence of cylindrical adhesion systems. We demonstrate that optimal adhesion can be achieved by either length scale reduction, or by optimization of the shape of the surface of the adhesion element. We find that whereas change in shape can lead to optimal adhesion strength, only reducing the dimension results in robust adhesion devices. An important consequence of this finding is that even under presence of surface roughness, optimal adhesion is possible provided the size of contact elements is sufficiently small. Our atomistic results corroborate earlier theoretical modeling at the continuum scale (Gao and Yao, PNAS, 2004). We discuss the relevance of our studies with respect to nature’s design of bone nanostructures and nanoscale adhesion elements in Geckos.
9:00 PM - Z3.19
Atomistic Modeling of Deformation Twinning in Nanocrystalline Cobalt.
Guangping Zheng 1
1 Mechanical Engineering, The University of Hong Kong, Hong Kong Hong Kong
Show AbstractDeformation mechanism of nanocrystalline metals with typical grain size of tens of nanometers is an interesting issue since dislocation slip is unlikely dominant in these materials. Recently it has been observed by experiments that deformation twinning plays an important role in cobalt nanocrystals. In this study, molecular dynamics simulation is employed to investigate the atomistic details of deformation twinning in nanocrystalline hcp cobalt. The plastic deformation is observed to induce an hcp-to-fcc allotropic transformation and consequently trigger twinning structures in an fcc matrix. First-principles calculation is further employed to explain the twinnability and lamellar fcc phase in hcp cobalt during deformation.
9:00 PM - Z3.2
Size Related Plasticity Effects in AFM Silicon Cantilever Tips.
Malgorzata Kopycinska-Mueller 1 , Roy Geiss 1 , Donna Hurley 1
1 Materials Reliability Division, NIST, Boulder, Colorado, United States
Show Abstract9:00 PM - Z3.21
Modelling of the Glass Transition of Oertho-terphenyl in Bulk and Thin Films.
Jayeeta Ghosh 1 , Roland Faller 1
1 Chem Eng & Mat Sci, UC Davis, Davis, California, United States
Show Abstract9:00 PM - Z3.22
Size-Dependent Elastic Moduli of Nanofilms
Shih-Hsiang Chang 1 , I-Ling Chang 2
1 Mechanical Engineering, Far East College, Tainan Taiwan, 2 Mechanical Engineering, National Chung Cheng University, Chia-Yi Taiwan
Show AbstractA semi-continuum model is presented to study the size dependence of the elastic properties for nanofilms. Unlike the classic continuum theory, the current model directly takes the discrete nature in the thickness direction into consideration. In-plane and out-plane Poisson's ratios as well as in-plane Young's modulus are investigated using this model. It is shown that the values of Young's modulus and Poisson's ratios depend on the total number of atomic layer in the thickness direction and approach the bulk values asymptotically.
9:00 PM - Z3.23
Shear-rate and Temperature Dependent Strength of SWNT Bundles: Creep of the Cross-links.
Boris Yakobson 1 , Yu Lin 1
1 MEMS, Rice University, Houston, Texas, United States
Show AbstractCross links have been discussed as reinforcement for the single-walled carbon nanotube (SWNT) bundles. Now we propose a phenomenological model of strength and yield of SWNT bundles via the movement of the inter-tube cross links, at finite temperature and shear rate, V. Further, the dynamics of specific chemical link is treated as a shear-modulated chemical reaction: the energy surface and transition states are computed with quantum-mechanical methods as function of tube-tube displacement. Due to possibility of the thermally-activated link relocation (creep), the strength S of the bundle (or fiber) depends on the shear rate and temperature. Analytical formulae for the resultant strength are obtained for two limits: (i) high shear rate or low temperature, S ~ const + ln (V/Vo), similar to known tribology relationship; (ii) slow shear limit, S ~ V/T. Molecular dynamics simulation of two carbon nanotubes with a >C=C< cross link reveals the details of such "creep". Based on computed energy and barrier parameters, we further conducted series of Monte Carlo simulations of multiple (up to a thousand) cross links connecting two narrow SWNT. The results at various rate V and temperature T agree with the derived formulae, and show that typical realistic conditions correspond to the high shear rate (i.e. low T) regime. This work is supported by the Office of Naval Research (DURINT) and by NASA (URETI TIIMS).
9:00 PM - Z3.24
Thermo Mechanics of Pre-stressed Polydimethylsiloxane Carbon Nanotube Composite.
Suresh Valiyaveettil 1 2 3 , Jinu Paul 1 , Sindhu Swaminathan 3 , Nurmawati Bte Muhammad Hanafiah 1 , Ajikumar Parayil Kumaran 2
1 Department of Chemistry, National University of Singapore, Singapore Singapore, 2 Singapore - MIT Alliance, National University of Singapore, Singapore Singapore, 3 NUSNNI, National University of Singapore, Singapore Singapore
Show Abstract9:00 PM - Z3.25
Raman Spectroscopy Investigation of Carbon Nanowalls.
Zhenhua Ni 1 , Haiming Fan 1 , Yuanping Feng 1 , Zexiang Shen 2 , Haoming Wang 3 , Yihong Wu 3
1 physics, National University of Singapore, singpoare Singapore, 2 Physics and applied Physics, Nanyang Technological University, Singapore Singapore, 3 Electrical and Computer Engineering, National University of Singpore, Singapore Singapore
Show AbstractThe two-dimensional carbon nanostructures carbon nanowalls (CNWs) have been grown vertically on the catalyzed substrates using microwave plasma-enhanced chemical vapor deposition (PECVD) [1-2]. The large surface area of aligned carbon nanowalls are useful as templates for the fabrication of other types of nanostructure materials, and would provide much potential applications in energy storage and electrodes for fuel cell [3-4].The growth of carbon nanowalls has been described in detail in refs1-2. Scanning Electron Microscopy (SEM) was used to observe the morphology of the film sample. Micro-Raman measurements were recorded in different sample orientations and polarizations. And also, Raman spectra were taken by different excitation lasers: 325 and 633nm (Renishaw Raman system), 488, 514.5 and 532nm (Jobin-Yvon T64000 Raman system). All the Raman spectra were measured in the backscattering geometry and at room temperature. The output power of excitation laser is below 1 mW, to ensure that the lasers do not heat the samples, which will make the peak shift. The resolution of the Micro-Raman is below 1cm-1, and the laser focus point is about 1 micron in diameter (with 100 magnification lens). All the observed peaks were assigned and compared with graphite. The G band of CNWs shifts slightly to higher frequency while its full width at half maximum (FWHM) is broader than that of graphite, indicating the finite size effect. The extremely strong D band of CNWs was thought due to the high edge density. While in different sample orientations and laser polarization, the ID/IG of the five conditions is 2.43(a), 2.31(b), 1.48(c), 1.46(d) and 1.35(e) respectively. This difference may be due to the Z polarization effect of G band. Different laser line was used to excite the sample, the laser energy dependence of the frequency of D band shift with the slope of 46.19 cm-1/eV has been observed, and the results agree well with the theoretical value by double resonance effect [5]. The 2D and G’ band shifts with the rate of 107.5 and 48.98 cm-1/eV respectively. And also, the decreasing intensity ratios ID/IG and ID’/IG with the increasing laser energy are observed and discussed.References[1] Y. H. Wu, P.W. Qiao, T.C. Chong, and Z.X. Shen, Adv. Mater. 2002, 14: 64[2] Y. H. Wu and B.J. Yang, Nano Letters 2002, 2: 355[3] M. Hiramatsu, K. Shiji, H. Amano, and M. Hori, Applied Physics Letters 2004, 84: 4708[4] B.J.Yang, Y.H.Wu, B.Y. Zong and Z.X. Shen, Nano Letters 2002, 2: 751[5] C. Thomsen and S. Reich, Physical Review Letters 2000, 85: 5214.
9:00 PM - Z3.26
Controlled Growth of Separated and Aligned Carbon Nano Tubes using Hydrogen Plasma and Nickel Film Interaction.
Santanu Patra 1 , Mohan Rao 1
1 Department of Instrumentation, Indian Institute of Science, Bangalore, Karnataka, India
Show Abstract9:00 PM - Z3.27
Carbon Nanotube Oscillator Operation by Encapsulated Gas Expansion.
Jeong Won Kang 1 , Ki Oh Song 1 , Jun Ha Lee 2 , Hoong Joo Lee 2 , Oh Keun Kwon 3 , Young-Jin Song 4 , Ho Jung Hwang 1
1 School of Electrical and Electronic Engineering, Chung-Ang University, Seoul Korea (the Republic of), 2 , Sangmyung University, Chonan Korea (the Republic of), 3 , Semyung University, Jecheon Korea (the Republic of), 4 Electronic Information Engineering, Konyang University, Nonsan Korea (the Republic of)
Show Abstract9:00 PM - Z3.29
Forming of Ceramic Nanocomposites using Spark Plasma Sintering Technology
Dustin Hulbert 1 , Dong Tao Jiang 1 , Amiya Mukherjee 1
1 Chemical Engineering & Materials Science, University of California, Davis, California, United States
Show Abstract9:00 PM - Z3.3
Depth-Dependent Nanomechanical Response of Soft Biomaterials.
Cheng Li 2 , Lisa Pruitt 1
2 Bioengineering, UC Berkeley, Berkeley, California, United States, 1 Mechanical Engineering, UC Berkeley, Berkeley, California, United States
Show AbstractRecently there has been an increase in the application of nanoindentation to non-traditional materials such as polymers and biological tissues. Amongst efforts to increase the utility of instrumented nanoindentation are investigations into alternative parameters for characterizing these materials at the micron/nano length scales (Ebenstein, 2002). Effects which complicate interpretation of mechanical measurements include surface roughness, time dependence, heterogeneity, and anisotropy. Recently the role of adhesion has been examined (Carrillo et al., 2005; Ebenstein and Wahl 2005). However depth-dependent properties of highly compliant and structured materials have not yet been fully characterized. The observed depth-dependence of hardness and modulus values particularly at shallow indentation depths, known as indentation size effect (ISE), is well acknowledged in the nanoindentation community (Lee et al., 2005; Xu and Zhang, 2004). In this work we examine the depth-dependent nanomechanical response of polycarbonate, agarose gel, and articular cartilage tissue. For comparative purposes, the same protocol is applied to the standard fused silica.
9:00 PM - Z3.30
Carbon Nanotube Based “Nose” For Detecting Of Aliphitic Hydrocarbons.
Sudhaprasanna Padigi 1 , Shalini Prasad 1
1 Electrical and Computer Engineering, Portland State University, Portland, Oregon, United States
Show AbstractDetection of hydrocarbons has a broad impact in terms of environmental monitoring of pollutants. We report the use of chemically functionalized carbon nanotubes as an “electronic nose” to detect the presence of aliphatic hydrocarbons like ethanol, methanol, proponal and butanol. We have adopted the approach of integrating the microfabrication techniques with nanomaterials like carbon nanotubes. We demonstrate to selectively pattern and trap the carbon nanotubes on a micro-electrode array using electrophoresis and di-electrophoresis by creating non-uniform electric field effects on the chip and also by creating nano trenches on the order of a few hundreds of nanometers on the chip. These patterned clusters of nanotubes are selectively exposed to the above mentioned hydrocarbons resulting in the detection of multiple hydrocarbons simultaneously on a single chip. We also compare the performance of a randomly aligned homogeneous distribution of nanotube array with that of a selectively positioned and aligned nanotube array for sensing applications. We also intend to compare the single-walled nanotubes versus multi-walled nanotubes from the sensing perspective. This is believed to be an important step towards the realization of reliable and practical nano-scale sensors and it also allows us to explore the possibilities of creating nano-scale electronic and photonic devices.
9:00 PM - Z3.31
Surface Morphology of GaInP Grown on GaAs Vicinal Substrates with Ga Content Increasing.
Hao Wang 1
1 , South China Normal University, Guang Zhou China
Show Abstract9:00 PM - Z3.32
White MicroBeam Analysis of the Near Surface Nanostructure State in Ti After Friction Stir Processing
Rozaliya Barabash 1 , G. Ice 1 , O. Barabash 1 , Z. Feng 1 , S. David 1
1 Metals and Ceramics Div., Oak Ridge National Laboratory, Oak Ridge TN, Tennessee, United States
Show AbstractSpatially resolved white beam Laue X-ray nano- and micro- diffraction at the synchrotron together with scanning electron and orientation imaging microscopy were used to characterize the structural changes in the Ti near surface region after Friction Stir Processing (FSP). It was established that after FSP a special surface layer with nanocrystalline structure is formed within the depth of 300 microns. Grain size within this zone is within the depth of 30-60nm. Probing of this zone with a white microbeam (diameter ~0.5 microns) did not get any detectable signal. However probing of this zone with the white nanosize beam (diameter ~100nm) gave a distinct diffraction patter. Typically several grains were observed within each probing location. Most of the diffraction pattern consisted of long streaked Laue spots. Such streaking is indicating strong plastic deformation in this zone with the formation of strain gradients, geometrically necessary dislocations and boundaries, and resulting in the local lattice curvature in each grain. Two specific zones are formed underneath the above nanocrystalline layer: thermal mechanical affected zone (TMAZ) and heat affected zone (HAZ). The size and structure of all zones is determined. The grain size increased sharply (by two orders of magnitude) from FSZ to TMAZ zones and reached micron size (5 - 30 microns) in the TMAZ. Then grain size decreased again and reached the size typical for base material. Intensive streaking of the Laue spots are observed with a microbeam in the TMAZ and HAZ zones. Large densities of geometrically necessary dislocations and strain gradients are found in the TMAZ based on Laue microdiffraction. Dislocation density gradually decreases with depth and reaches the value typical for base material. The geometrically necessary dislocations were inhomogeneously distributed within the TMAZ and HAZ. Inhomogeneity of geometrically necessary dislocations distribution was found at both scales: within the individual grains and between separate grains.
9:00 PM - Z3.33
Biomechanical Characterization of the Murine Fracture Callus
Shikha Gupta 1 , Fernando Carrillo 5 , Ralph Marcucio 4 , Christian Puttlitz 3 , Lisa Pruitt 2 4
1 Applied Science and Technology, University of California, Berkeley, Berkeley, California, United States, 5 Chemical Engineering, Polytechnique University of Catalonia, Barcelona, Terrassa, Spain, 4 Orthopaedic Surgery, University of California, San Francisco, San Francisco, California, United States, 3 Mechanical Engineering, Colorado State University, Fort Collins, Colorado, United States, 2 Mechanical Engineering, University of California, Berkeley, Berkeley, California, United States
Show AbstractApproximately 6 million people in the United States sustain skeletal fractures each year. Although advances in orthopaedic technology have improved greatly during the past 25 years, more than 10% of fractures still heal incompletely. The want for better tr