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Short Range Order and the Evolution of Deformation Mechanisms in Both High and Low Entropy Alloys: Nano Seminar series
April 22, 2022 @ 2:00 pm - 3:00 pm
Prof. Andrew M. Minor, UC Berkeley, Materials Science & Engineering
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.
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Andrew Minor did his PhD in MSE here at UC Berkeley (Go Bears!) and is currently the facility director at the NCEM LBNL Molecular Foundry. 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)