Effect of Microstructure on Tensile Properties and High-Cycle Fatigue Behavior of a Low-Cost Ti-6Al-4V Alloy

Abstract:

A low-cost Ti-6Al-4V (TC4) alloy fabricated by remelting TC4 scrap using electron beam cold hearth melting (EBCHM) combined with a short-process hot-rolling route was investigated. Two heat treatment conditions, namely stress-relief annealing and solution treatment followed by aging were adopted to study the influence of microstructure on the tensile properties and high-cycle fatigue (HCF) performance of the alloy. The results indicate that the stress-relieved alloy exhibits a typical basketweave α+β lamellar microstructure. After solution treatment and aging, the microstructure transforms into a heterogeneous structure consisting of coarsened α lamellae, equiaxed α grains, and transformed β. Compared with the annealed condition, the solution-aged alloy shows a significant improvement in ductility while maintaining relatively high strength, leading to a favorable strength-ductility synergy. This enhancement is primarily attributed to the cooperative deformation of coarsened α lamellae and equiaxed α grains, which effectively accommodate dislocation slip and promote the activation of higher-order slip systems, thereby improving the plastic deformation capability of the alloy. High-cycle fatigue tests reveal that the annealed alloy exhibits a higher fatigue strength. This behavior is associated with the basketweave lamellar microstructure, which facilitates crack deflection and prolongs the fatigue crack propagation path, thereby improving resistance to fatigue crack growth.