The silicide precipitation mechanism and spheroidization behavior of αp phase in a novel near-β titanium alloy during isothermal multi-directional forging process

Abstract

The tread-off between the strength and ductility of near-β titanium alloys has significantly limited their applications. In this study, a novel near-β titanium alloy containing Si element was designed, and the influence of α-phase spheroidization and silicide precipitation on the mechanical properties was investigated during isothermal multi-directional forging (IMDF) process. The results showed that the β grain is easy to deform and elongate, and the deformed alloy mainly undergoes dynamic recovery (DRV) rather than dynamic recrystallization (DRX). Some silicides are dissolved due to the temperature rise caused by IMDF and the diffusion of atoms on the top of the irregularly shaped silicides. Zr and Si elements are redistributed and segregated at the dislocation, resulting in the formation of submicron-scale and nano-scale silicides. Lath-like α_p phase will precipitate from the prior β grain after heat treatment in the dual-phase region, and the volume fraction of α_p phase increases with the decrease of heat treatment temperature. In addition, rotation deformation and spheroidization of the lath-like α_p phase occur during multi-pass IMDF in the dual-phase region. When multi-pass IMDF temperature is 770 ℃, the silicide distribution is uniform, and the α_p phases are equiaxed, which is conducive to the improvement of ductility. The obtained results provide a new way to prepare the Si-containing near-β titanium alloys with excellent mechanical properties.