Novel deformation twinning system in a cold rolled high-strength metastable-β Ti-5Al-5V-5Mo-3Cr-0.5Fe alloy

A high-strength metastable beta-titanium alloy, Ti-5Al-5Mo-5V-3Cr-0.5Fe (wt.%) was cold rolled at room temperature and characterized using scanning and transmission electron microscopy. A novel {10 9 3}< 331 >(beta) type deformation twining mode (Sigma 19a) is reported for the first time, and crystallographic analysis was carried-out to elucidate the origin of such high-index deformation twins. The initially beta-solutionized alloy contains nano-scale omega phase, which is also subsequently distributed within the twins. Additionally, a thin nano-scale omega layer forms along the twin boundaries, and two variants of alpha '' martensite phase form inside the deformation twins. The current work opens up new prospects for improving the ductility of high-strength Ti alloys by inducing the twinning and transformation induced plasticity effects.