Deciphering the effect of α phase on tensile-creep deformation of high-temperature Ti65 titanium alloy

Creep resistance is a key performance metric of high temperature structural components in aeronautics and space manufacturing field, and the strong dependency of creep deformation on α phase morphology requires careful consideration in titanium alloy. The dependency of tensile-creep deformation on α phase morphology of Ti65 titanium alloy sheet at 650 °C has been systematically investigated. The endurance time of creep property could be increased from 7.7 h to 237.5 h by controlling the volume of equiaxed α phase. The article focuses on the analysis of the specimens (M1and M2) with two typical microstructure which have creep endurance time of 7.7 h–9.7 h and 225.0 h–237.5 h respectively at 650 °C and 240 MPa. Fracture morphology of M1 and M2 specimens was characterized, revealing different fracture modes for M1 and M2. The two samples exhibited different deformed microtexture and the average Kernel Average Misorientation (KAM) value. The micro-cracks in M1 and M2 both initiate at the phase interface with a high misorientation value. Crack propagation diverged fundamentally: M1 cracks propagate along equiaxed α grain boundary, but the micro-cracks in M2 propagate along grain boundary and through α lamella in a tortuous path. Finally, it is clarified that the significant difference of creep property resulted from distinct deformation mechanisms, with grain boundary sliding coupled dislocation slip governing M1 failure, and dislocation slip within fine α lamellae dominating M2. These findings establish α-phase morphology optimization as an effective strategy for enhancing creep resistance in high-temperature titanium alloys.