Effect of α Phase on Dynamic Mechanical Properties and Failure of Ti-4Al-5Mo-5V-5Cr-1Nb Alloy after Two-Stage Aging

This work studied the high strain rate behavior of the Ti-4Al-5Mo-5V-5Cr-1Nb (Ti-45551) alloy after two-stage aging, with dynamic tension tests conducted using the split Hopkinson tensile bar. The results show that the microstructure, especially the size and distribution of the α phase, significantly affects the mechanical and failure behaviors of the Ti-45551 alloy under dynamic loading. As the strain rate increases, increasing trends can be observed in both ductility and strength, which is intimately related to the activation of the dislocation slip in the α phase. Moreover, obvious strain softening was found in the Ti-45551 alloy under dynamic loading. In this study, the microstructure observations suggest that dislocation slips are highly active in the α phase under dynamic loading. Fractographic characterization of the fracture surfaces under dynamic loading reveals a uniform distribution of ductile dimples, which indicates that a uniform distribution of the nano-scale α phase can effectively reduce brittle fracture tendency. Our studies provide a comprehensive picture of how strain rate drives dynamic plasticity and failure mode in the Ti alloy