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 degrees C) plus aging (580-640 degrees C) treatments were investigated. The results show that the volume fraction of the primary alpha (alpha(p)) phase decreases with the increase of solution temperature, and the length of the secondary alpha phase (alpha(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 degrees C for 2 h plus aging of 640 degrees C for 8 h, in which the tensile strength is 1434 MPa and the elongation is 7.7%. The coarsening alpha(s) phase makes crack propagation paths deflected and tortuous, which increases the crack propagation resistance and improves the ductility and fracture toughness.