Microstructure evolution during solution treatment and its effect on the tensile properties at 700 °C of a novel near-α high temperature titanium alloy

Abstract

To achieve a synergistic combination of high strength and ductility in titanium alloys at 700 °C, a novel near-α high temperature titanium alloy Ti–5.8Al–4.0Sn–4.0Zr–0.31Nb–0.62Ta–1.26W–0.4Si was designed. The microstructure was subsequently optimized through hot forging followed by heat treatment, and its microstructural evolution was systematically investigated. Results indicated that with increasing solution temperature from 950 °C to 1050 °C, the volume fraction of primary equiaxed α phase (α_p) decreased while the transformed β phase (β_t) and secondary lamellar α phase (α_s) increased. The microstructure evolved from predominantly equiaxed α to a lamellar structure. Tensile tests conducted at 700 °C revealed that the samples solution-treated in the upper half of the α+β region (1000 °C) exhibited the superior combination of strength and ductility, achieving a tensile strength of 576.2 MPa while maintaining an elongation of 22.3%. The superior mechanical properties can be attributed to the refined α_p and β_t phases. The dislocation motion is hindered by fine α_s lamellae while interfacial pinning effects combined with an oriented arrangement of dispersed S₂ silicide precipitates contribute to synergistic strengthening.