Enhancement of uniform elongation in high strength Ti–Mo based alloys by combination of deformation modes

A combination of different deformation modes, namely, dislocation slip and {3 3 2}〈1 1 3〉 twinning was found to be effective for achieving high yield strength and large uniform elongation in the β type Ti–15Mo–5Zr and Ti–10Mo–2Fe alloys in the as-solution treated condition, where the Mo equivalency was designed to be between 15.3 and 18.7 mass%. The high yield strength was caused mainly by the slip, and the large uniform elongation was caused by the twinning through significant work hardening. The change in the work hardening rate with strain correlated well with the formation of mechanical twins. The deformation was heterogeneous among the grains and the twins were not seen in some of the grains even after the tensile fracture. This heterogeneity was discussed based on the effects of the grain orientation and the segregation of alloying elements.