In-situ investigation on tensile deformation and fracture behaviors of a new metastable β titanium alloy

The tensile deformation and fracture behaviors of a new metastable beta titanium alloy (Ti-5Cr-4Al-4Zr-3Mo-2W-0.8Fe) with single beta phase are investigated by in-situ tensile test under scanning electron microscopy. With the increase of deformation degree, in addition to the transition from single slip to multiple slip, the stress induced martensite (SIM) and mechanical twins will also occur to coordinate the overall deformation of the alloy, leading to further work hardening. The slip system activation, slip transfer and grain rotation are closely related to the crystallographic orientation, which can be evaluated by Schmid factor, geometric compatibility factor and misorientation. The dislocation pile-up leads to serious stress concentration and inhomogeneous deformation appeared in the areas near grain boundary, dislocation line and shear band, and the microvoids are easy to nucleate and grow in the above areas and then coalescence into microcracks. The primary crack formed by microcrack extension propagates along the activated slip system in the grain, and deflects as it passes through the grain boundary to coordinate the slip system in the adjacent grain, resulting in the overall crack propagation path being zigzag. Considering the damage prone location and crack propagation path, it can be concluded that the fracture mechanism of the alloy belongs to the intergranular and transgranular mixture.