Mechanical properties and deformation mechanisms of near-β titanium alloys: multi-scale α phase microstructure
摘要
Optimizing the mechanical performance of near-β titanium alloys requires a clear understanding of how multi-scale α phase morphologies influence tensile deformation behavior. This study aims to elucidate the relationship between the α phase fractions tailored by different heat treatment conditions and the resulting tensile response of a Ti-5Al-5Mo-5V-1Cr-1Fe alloy. Microstructural characterization and tensile testing were conducted on specimens with varying proportions of primary (αp) and secondary (αs) α phases. The results show that microstructures with a higher volume fraction of αp and a lower volume fraction of αs can achieve a favorable balance between ultimate tensile strength and fracture strain (1190.3 MPa, 7.85%). This is attributed to the reduced amount of αs, which allows dislocations to migrate toward the vicinity of the αp, thereby enabling the αp to accommodate plastic deformation through coordinated dislocation slip. In contrast, alloys with increased αs content exhibit significantly higher strength (1479.7 MPa) but reduced ductility (3.17%), as the αs phase strongly pins dislocations and constrains plastic deformation. In microstructures with a high content of αp and a relatively low content of αs, the pinning effect of αs is weakened, allowing dislocations to glide more readily and rendering deformation predominantly governed by dislocation slip. The equiaxed αp phase facilitates the activation of multiple slip systems, whereas the rod-like αp phase tends to promote single-slip deformation. Overall, the hierarchical distribution of multi-scale α phases enables uniform strain accommodation, leading to an improved strength and ductility synergy in the Ti-5Al-5Mo-5V-1Cr-1Fe alloy system.