Effect of transformed β phase on fish-eye ductile crack initiation of a Ti-6Al-4V alloy in very high cycle fatigue regime

Abstract Very high cycle fatigue (VHCF) properties and damage mechanisms were investigated for a Ti-6Al-4V alloy with needle-like β phase. It was revealed that the fatigue damage is dominated by interior crack initiation with a fish-eye pattern. The center of the fish-eye area is covered by peaks, dimples, microvoids and grooves, exhibiting micro-ductile characteristics instead of the commonly reported brittle ones. It was found that the formation of this particulier appearance resulted from the nucleation and coalescence of microvoids and grooves essentially occurring in the transformed β phase (βt). The βt phase played a dominant role in the crack initiation process of the Ti-6Al-4V in the VHCF regime.