In-situ study on tensile deformation and damage evolution of metastable β titanium alloy with lamellar microstructure

Tensile deformation and damage evolution of a metastable beta titanium alloy (Ti-5Cr-4Al-4Zr-3Mo-2W-0.8Fe) with lamellar microstructure are studied by in-situ tensile test under scanning electron microscopy. In the tensile process, the main deformation modes include the dislocation slip, phase interface shear and grain boundary shear, and the geometrical orientation of alpha lamellae determines the activation of different slip systems and whether the interface shear is involved in deformation. The a lamellae may kink and even fragment under severe deformation. Slip transfer is prone to occur between alpha lamella and beta interlayer that satisfy the Burgers orientation relationship, and the slip lines will deflect and bifurcate as more slip systems are activated and grains rotate. Due to the localized stress concentration and inhomogeneous deformation, the grain boundaries, phase interfaces, tips of beta interlayers, junctions of colonies composed of alpha lamellae and shear bands are all the positions where are easy to generate microvoids. The crack propagates along a zigzag path on account of the synergistic reaction mechanism of critical resolved shear stress, activated slip system, shear band and grain boundary shear, resulting in an intergranular and transgranular mixed fracture mode.