Effect of solution plus aging heat treatment on microstructural evolution and mechanical properties of near-β titanium alloy

The microstructural evolution, mechanical properties and fracture mechanism of a Ti–5Al–5Mo–5V–3Cr–1Zr (Ti-55531) alloy after solution (760–820 °C) plus aging (580–640 °C) treatments were investigated. The results show that the volume fraction of the primary α (α_p) phase decreases with the increase of solution temperature, and the length of the secondary α phase (α_s) decreases while its width increases with the increase of aging temperature. Yield and tensile strengths decrease with the increase of solution temperature, while increase with the increase of aging temperature. A good balance of tensile strength and ductility of the alloy is obtained under solution of 800 °C for 2 h plus aging of 640 °C for 8 h, in which the tensile strength is 1434 MPa and the elongation is 7.7%. The coarsening α_s phase makes crack propagation paths deflected and tortuous, which increases the crack propagation resistance and improves the ductility and fracture toughness.