Phase transformation behavior of Ti-1023 under static heat treatment and dynamic thermo-mechanical coupling

Abstract

The phase transformation of a near-β titanium alloy is extremely sensitive to the processing technique, which significantly affects its mechanical characteristics. The spherical α phase increases the plasticity of a β titanium alloy, whereas its needle-like α phase prevents dislocations and increases the alloy strength. In this study, we investigate the microstructural evolution and orientation relationship of Ti-1023 alloy under static heat treatment and dynamic thermo-mechanical coupling at 750 °C. The results indicate that under the thermo-mechanical coupling conditions, the spherical α phase precipitates at grain boundaries and low-angle grain boundaries, and its volume fraction increases from 10.5% to 23.2% as the strain rate decreases. The Burgers orientation relationship (BOR) between the α/β phases is gradually disrupted as the strain rate increases. On heat treatment, the α phase at the grain boundaries becomes discontinuous in a strip-like shape, whereas that within the grain appears needle-like. The grain-boundary α phase becomes more continuous as the heat treatment duration is extended, and the α phase gradually broadens. Moreover, the precipitated α more tends to obey the BOR. These results could provide important reference for the regulation of the microstructure of a near-β titanium alloy and the optimization of the process parameters of its deformation heat treatment. • Phase transition behavior of Ti-1023 alloy under thermo-mechanical coupling and static heat treatment conditions was investigated. • The α phase is spherically precipitated under thermal coupling conditions, and the volume fraction reaches a maximum at a strain rate of 0.001 s −1 • Under static heat treatment conditions, α phase precipitates needle-like and gradually broadens with increasing heat treatment time. • Schematic of α phase precipitation under thermal-mechanical coupling and static heat treatment of the alloy.