Understanding cross boundary {332} 〈113〉 twins in a Ti-15Mo alloy by composite Schmid factor

Abstract

This work aims to understand the cross-boundary behavior of {332}〈113〉 twinning in a metastable β type titanium alloy: Ti-15Mo alloy, especially the variant selection mechanism by evaluating Schmid factor (SF), geometric compatibility factor ( m ′) and a recently proposed composite Schmid factor (CSF). Statistical results showed that >40% of the observed paired twins do not have the first SF rank, suggesting that non-Schmid twins might be promoted by the cross-boundary behavior. By contrast, all the sequential twinning selected the variant with the first CSF rank and even 79% of the simultaneous twinning selected the variants with the first CSF rank, which indicates that CSF is more effective than SF for twin variant prediction in Ti-15Mo alloy. The superiority of CSF over m ′ for predicting simultaneous twinning was also discussed. Moreover, the influence of boundary angle on twinning transfer behavior was revealed and explained based on the CSF analysis. • Non-Schmid {332}<113 > twinning was promoted by the cross-boundary behavior in Ti-15Mo alloy. • Composite Schmid factor is effective in predicting the variants of such cross-boundary twins. • Twin transfer likely occurred at lower angle boundaries, which was explained by CSF analysis.