Microstructural tailoring and mechanical properties of a multi-alloyed near β titanium alloy Ti-5321 with various heat treatment

A new near β-Ti alloy Ti-5Al-3Mo-3V-2Cr-2Zr-1Nb-1Fe (Ti-5321) with a unique combination of high strength and good fracture toughness was designed. The microstructure was tailored by changing the solution and ageing conditions, and the influences of microstructural evolution on tensile properties and fracture toughness of the alloy were investigated. The results showed that the volume fraction and size of primary α phase were decreased with increasing the solution temperature, while the morphology of secondary α precipitates was related to ageing temperature. The ultimate tensile strength (UTS), total elongation (EL) and fracture toughness can be achieved in a range of 1147-1439 MPa, 3-26% and 57-76 MPa m1/2, respectively, depending on the heat treatment parameters. An excellent balance of high strength and good ductility was realized after the solution treatment at 830 °C and ageing at 620 °C for 480 min, in which the UTS, EL and fracture toughness were 1238 MPa, 20% and 73 MPa m1/2, respectively. Morphological features of the fractography were discussed against the different microstructural morphologies, and this provided further information on the fracture behavior of the alloy.