Deformation and Transitions at Grain Boundaries VII: Poster Session
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Computational Materials Science and Engineering Committee
Program Organizers: Saryu Fensin, Los Alamos National Laboratory; Thomas Bieler, Michigan State University; Shen Dillon, University of California, Irvine; Douglas Spearot, University of Florida; Jian Luo, University of California, San Diego; Jennifer Carter, Case Western Reserve University
Monday 5:30 PM
February 24, 2020
Room: Sails Pavilion
Location: San Diego Convention Ctr
G-8 (Invited): Novel X-ray Tools to Study Size Effects on Nanocrystalline Materials: Anastasios Pateras1; Jonathan Gigax1; Kevin Baldwin1; Wonsuk Cha2; Ross Harder2; Richard Sandberg3; Saryu Fensin1; Reeju Pokharel1; 1Los Alamos National Laboratory; 2Argonne National Laboratory; 3Brigham Young University
Macroscopic properties of crystalline materials dramatically depend on nanoscale structure and dimensionality. Elastic constants are typically defined with respect to bulk while their values deviate and need to be measured explicitly in the case of two-dimensional materials or nanometer-sized objects. Particularly in really small dimensions, the crystallographic orientation plays an important role in the mechanical behavior of materials. Thus, in addition to measuring atomic displacements, the knowledge of the crystallographic orientation is needed. Laue diffraction with a large bandwidth x-ray (pink) beam allows determining the crystallographic orientations of crystals. Here we present a new movable monochromator, recently commissioned at the APS 34-ID-C beamline, that allows to easily switch from a pink x-ray beam to a monochromatic beam for Laue diffraction and Bragg coherent diffraction imaging, respectively, in the same experimental setup. We demonstrate the first results and discuss future research in diverse areas of materials science and condensed matter physics.
G-9: Deformation Nanomechanics and Dislocation Quantification at Atomic Scale in Nanocrystalline Pure-metal Magnesium: Md Shahrier Hasan1; Wenwu Xu2; 1San Diego State University and University of California, San Diego; 2San Diego State University
Classical Molecular Dynamic Simulation method is used for uni-axial tensile deformation of nanocrystalline magnesium of varied mean grain size from 6 nm to 45 nm. The deformation nano-mechanics reveals two distinct deformation mechanism. For larger grain size, conventional dislocation dominated deformation is observed while for smaller grain size, predominantly grain boundary atoms participate in the deformation process where different grain boundary-based mechanism is observed such as grain boundary sliding, grain boundary rotation etc. Dislocation quantification further supports this observation and shows that the change in dislocation density in the sample drastically reduces with decreasing grain size particularly at the yield point where new dislocation nucleation occurs by deformation. A comparative analysis of the grain size dependent mechanical properties reveals a gradual transition from grain boundary dominated stress-strain curve profile to dislocation dominated stress-strain curve profile as the grain size of the sample is increased from 6 nm to 45 nm.
G-10: Investigation of Grain Boundary and Dislocation Interactions Through In-situ TEM MEMS-based Tensile Nanomechanical Testing of Ultrafine Grained Gold Thin Films: Sandra Stangebye1; Saurabh Gupta1; Yin Zhang1; Joshua Kacher1; Olivier Pierron1; Ting Zhu1; 1Georgia Institute of Technology
Due to the small average grain size and high-volume fraction of grain boundaries in ultrafine grained metals, grain boundaries play a crucial role in plastic deformation by acting as sites for nucleation of dislocations and as barriers to dislocation propagation. In this study, interactions between grain boundaries and dislocations in ultrafine grained gold thin films were investigated using a combination of quantitative in situ TEM nanomechanical testing, transmission Kikuchi diffraction (TKD), and atomistic simulations. Specifically, repeated stress relaxation tests were performed in situ on miniaturized dogbone samples and the physical activation volumes at different stages of deformation were found and related directly to the observed dislocation activity. These identified dislocation interactions were investigated in detail via atomistic simulations, providing greater insight into the atomic-scale mechanisms dictating the dislocation interactions. Results will be discussed in terms of the influence of grain and grain boundary characteristics on dislocation interactions.
G-11: The Chemical Effect on the Potential Energy Landscape of Grain Boundary: Sam Garretson1; Liang Tian1; Lin Li1; 1The University of Alabama
Grain Boundaries (GBs) determine many of the properties of materials such as their strength, creep deformation, fatigue, and corrosion. Understanding the kinetics of grain boundaries is crucial to understanding material properties. In this study, we investigate the kinetics of Cu Sigma 5 (210) and Al Sigma 5 (210) GBs that are created by Molecular Dynamics Simulations. Then their potential energy landscapes are probed by Activation-Relaxation Technique, composing the data of kinetic transition events. The potential energy landscapes of the two materials with identical orientation, but chemical distinction, GBs are compared, specifically focusing on the chemical effect on modulating the activation energetics of GB kinetic processes.