Effects of cryogenic treatments on phase transformations, microstructure and mechanical properties of near βTi alloy

The influences of cryogenic treatments, i.e. liquid nitrogen quenching (LNQ) and water quenching followed with liquid nitrogen immersion (WQ-L) on phase transformations, microstructural development and mechanical properties during aging treatment have been studied in near βTi-5Al-3Mo-3V-2Cr-2Zr-1Nb-1Fe alloy. The results showed that cryogenic treatments produced more O′ and ω-embryos in comparison with water quenching (WQ). After aging treatment, the LNQ sample and WQ-L sample formed finer and higher number density of α precipitates within β grains, which is attributed to the increase of O′ domains provides more potent nucleation sites for α. Tensile tests indicated that the cryogenic treatments improved tensile strength without trading-off ductility obviously. The ultimate tensile strength of aged LNQ and WQ-L sample was increased by 142 MPa and 62 MPa, respectively.