Effect of Microstructure on High Cycle Fatigue and Fatigue Crack Propagation Behaviors of β-Annealed Ti–6Al–4V Alloy

High cycle fatigue (HCF) and fatigue crack propagation (FCP) behaviors of β-annealed Ti64 alloys having a microstructure of either α colonies or basketweave were studied. It was found that the resistance to HCF of β-annealed Ti64 alloys with a microstructure of α colonies was similar but slightly inferior to those with a microstructure of basketweave. On the other hand, the FCP rates of β-annealed Ti64 alloys having a microstructure of α colonies were lower than those of basketweave, particularly in low ΔK regime. Crack path observation on the surfaces of β-annealed Ti64 alloy specimens suggested that crystallographic crack growth prevailed in the microstructure of α colonies, leaving cleavage facets on the fracture surface and less fatigue damage at the tip of crack. Based on the fractographic and micrographic examination, the effects of microstructure on the HCF and FCP behaviors of β-annealed Ti64 alloys were discussed.