Deformation mechanisms and kinetics of time-dependent twinning in an α-titanium alloy

Within the past decade, many studies have shown that twinning can occur in alpha, beta, and alpha + beta titanium alloys at speeds many orders of magnitude lower than the speed of sound. Traditionally, twinning has been described as a shear process that can occur almost instantaneously; however, the twinning deformation mechanisms in titanium alloys can be controlled by the diffusion of oxygen away from annihilated interstitial sites at the twin boundaries. The most recent studies which include the strain-rate effects on twinning support the hypothesis that twinning in these materials is controlled by a slow diffusion process rather than a quick shear process. The effects of strain-rate on twinning in a alpha-Ti-1.6V alloy were systematically investigated by means of optical and transmission electron microscopy and a diffusion-based model has been applied which explains the unexpected twin sizes observed at different strain rates. (C) 2012 Elsevier Ltd. All rights reserved.