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Short range order and the evolution of deformation mechanisms in both high and low entropy alloys

Andrew Minor
University of California, Berkeley
Online WebEx seminar
Tue, December 07, 2021 at 11:00 AM
This talk will describe our recent results utilizing energy filtered diffraction, 4D-STEM and in situ TEM nanomechanical testing that provide insight into multiscale deformation phenomena in α-titanium and the CrCoNi medium entropy alloy. Using energy-filtered TEM and HRSTEM techniques it is possible to directly image, and therefore quantitatively assess, SRO and its effect on mechanical properties. In order to understand the effect of SRO in terms of the evolution of plasticity at different stages, the technique of 4D-STEM was used during in situ deformation and fracture experiments. 4D-STEM can provide both real-space imaging and diffraction analysis during in situ testing, making it possible to perform strain mapping via diffraction pattern analysis during in-situ deformation in a TEM. The diffraction patterns are used to identify defects and map relative strain, while the images formed by using virtual apertures provide microstructural context for the analysis. In addition to using these techniques to investigate deformation in medium entropy alloys, this talk will also describe similar effects in pure Ti (a very low entropy alloy). In particular, we will discuss both alloying and processing strategies to mitigate or even eliminate the detrimental effects of O in Ti. These strategies will be discussed in terms of SRO, the evolution of dislocation structure during deformation (wavy vs. planar slip) and the correlation of brittle grain boundaries and twin types with oxygen content.
Andrew Minor

Andrew Minor is a Professor at the University of California, Berkeley in the Department of Materials Science and Engineering and also holds a joint appointment at the Lawrence Berkeley National Laboratory where he is the Facility Director of the National Center for Electron Microscopy in the Molecular Foundry. He received a B.A. in Economics and Mechanical Engineering from Yale University and his MS and Ph.D. in Materials Science and Engineering from U.C. Berkeley. He has co-authored over 230 publications and presented over 145 invited talks on topics such as nanomechanics, lightweight alloy development, characterization of soft materials and in situ TEM technique development. His honors include the LBL Materials Science Division Outstanding Performance Award (2006 & 2010), the AIME Robert Lansing Hardy Award from TMS (2012) and the Burton Medal from the Microscopy Society of America (2015).