Microstructure evolution characteristics of near-α TA32 titanium alloy during superplastic tensile deformation

Abstract

The characteristics of superplastic microstructure evolution and deformation behavior of rolled near-α TA32 titanium alloy were investigated at different deformation temperatures (920 °C, 940 °C, and 960 °C) and initial strain rates (1 × 10−3 s−1 and 3 × 10−3 s−1). Results show that TA32 alloy exhibited exceptional superplastic deformability with maximum elongation near 900%, and flow stress sensitivity to temperature as well as strain rate. Continuous dynamic recrystallization (CDRX) and dynamic recovery (DRV) mechanisms mainly controlled the flow softening process of TA32 alloy, which transformed low-angle grain boundaries (LAGBs) to high-angle grain boundaries (HAGBs). The main dislocation slip mode in αp phase was prismatic <a> slip, while basal <a> slip and pyramidal <c+a> slip gradually operated as the strain increased. The tensile deformation of rolled TA32 sheet was most ductile in the range of 40–55° from rolling direction (RD) to transverse direction (TD). Deformation and high temperatures caused the initial textures {112‾2}<11‾00> and {0001}<11‾00> to transform into multiple texture components with weak strength, such as (0001)[21‾1‾0], (011‾2)[45‾13], and (112‾4)[1‾3‾43]. The rotation of lattice/grain provided freedom for microstructure deformation. The superplastic deformation of TA32 alloy was controlled by a combination of deformation mechanisms. The main superplastic deformation mechanism was the relative sliding of grains along HAGBs, coordinated by dislocation motion, grain rotation, and dynamic recrystallization (DRX).