Deformation mechanism of the (β + α”) dual-phase Ti-42Zr-13Nb alloy exhibiting an abnormal work-hardening behavior

In-situ high-energy X-ray diffraction combined with post-mortem transmission electron microscopy was used to reveal the deformation mechanism of the (β + α”) dual-phase Ti-42Zr-13Nb (wt.%) alloy exhibiting a two-stage yielding behavior under tension. It is found that the first yielding stage is dominated by two processes, i.e., the reorientation of pre-existing α” phase via variant selection and the preferential induction of α” variants during martensitic transformation. These two processes make the {020}_α” plane perpendicular to the loading direction (LD) and lead to an abnormal increase in the work-hardening rate at 0.036–0.082 strain. When the strain exceeds 0.082, the stress-induced martensitic transformation ceases and the reorientation of pre-existing α” phase gradually weakens, resulting in a continuous decrease in the work-hardening rate. Moreover, the second yielding stage is dominated by the reorientation of stress-induced α” martensite, which tends to reorient the plane perpendicular to LD from {020}_α” to {110}_α”. Our investigation provides new insights into the reorientation scenarios of both pre-existing and stress-induced α” phases, as well as the underlying physical mechanism responsible for the abnormal work-hardening behavior in Ti-based shape memory alloys.