Effect of temperature on the transition in deformation modes in Mg single crystals

Abstract

Here, an experimental study utilizing in-situ scanning electron microscopy (SEM) micro-compression testing and post-mortem transmission electron microscopy (TEM) imaging is presented to quantify the effect of temperature on the transition in deformation modes in twin-oriented Mg single crystals. Single crystal micropillars were fabricated using FIB milling, then tested by in-situ SEM micro compression from 20 degrees C to 225 degrees C. It is observed that plasticity in the deformed Mg microcrystals at temperatures at and below 100 degrees C is governed by {10 (1) over bar2} extension twinning. However, an anomalous increase of the flow stresses is observed at 100 degrees C, which is likely due to paucity of dislocation sources that are required to promote twin boundary migration. At 150 degrees C and above, extension twinning is suppressed and a continuous plastic flow and strain softening induced by prismatic dislocation mediated plasticity is observed. By comparing the current results with those from bulk scale studies for other hexagonal-closed-pack single crystals (e.g. titanium (Ti) and zirconium (Zr)), a general trend for the effect of temperature on the transition in deformation modes in HCP materials is proposed. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.