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

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. [Display omitted] •Non-Schmid {332} 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.