Microstructure and Thermal Stability of High‐Temperature Titanium Alloy with Hf Element

Abstract

The influence of partial substitution of Hf for Zr on the microstructure and thermal stability of near-α high-temperature titanium alloys is systematically investigated. The results show that the addition of Hf promotes the refinement of precipitated phases of the silicides and α2 phase and the (Ti,Zr,Hf)6(Si,Sn)3 S2-type silicides were formed in alloys after aging treatment. During thermal exposure, both silicides and α2 phase in alloy with 2.5 wt% Hf exhibited excellent anti-coarsening ability, which may be attributed to the slow diffusion of Hf in Ti that significantly inhibited the growth rate of the precipitated phase. The loss of plasticity of near-α titanium alloys after thermal exposure is mainly due to the precipitation and coarsening of silicides and α2 phase, therefore, the Hf-containing titanium alloy has more excellent thermal stability, i.e., the plasticity loss rate is decreased from 34.8% (the alloy without Hf) to 7.4% (the alloy with 2.5 wt% Hf).