Ph.D. Candidate, University of California, Berkeley
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Presented: September 10 and 11, 2020
“Imaging of Chemical Short-range Order and Its Impact on Deformation in Structural Alloys”
Chemical short-range order (SRO) of atoms within a nominally single-phase solid solution is known to significantly impact the plastic deformation of alloys. While associated phenomena, such as planar dislocation slip morphology and ranging stacking fault energies, have been indirectly related to deformation behaviors, direct observation of the SRO microstructure at the nanoscale remains unexplored. Here we report the direct observations of SRO and associated deformation features in a Ti-Al alloy and a medium entropy alloy using energy-filtered dark field imaging. The observation revealed the domain clusters structure of the SRO and verified that the degree of SRO could be tailored by the thermomechanical history of the alloys. The impact of SRO on the deformation behaviors of the alloys, including dislocation motions and deformation twinning, are investigated at different scales. The atomistic interaction between SRO and deformation is probed via a full strain tensor mapping method based on four-dimensional scanning transmission electron microscopy, revealing the evolution of local bonding environment that is responsible for the slip planarity. The tool set developed in the current study grants the ability of conduct quantitative analysis of SRO and shines light upon a new avenue to engineer desirable performance of structural alloys.
Ruopeng Zhang, Ph.D. Candidate, University of California, Berkeley
Ruopeng Zhang is currently a Ph.D. candidate working at both the National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory and the Department of Materials Science and Engineering, University of California, Berkeley. His research interests include direct TEM observations of SRO in structural alloys, in-situ TEM nanomechanical testing of stress-induced phase transformations and method development of data analysis on both 4D-STEM and EBSD experiments.