Effects of tensile/compressive overloads on fatigue crack growth behavior of an extra-low-interstitial titanium alloy

In this paper, fatigue crack propagation tests of an extra-low-interstitial titanium alloy (Ti-6Al-4V ELI) were performed under various tensile/compressive overloads in an otherwise constant amplitude loading sequence. The effects of the tensile/compressive overloads on the crack growth rate, crack growth path and crack growth profile of the Ti-alloy were investigated. The results showed that the tensile overload resulted in an overload-ratio-dependent crack growth retardation, while almost no effect of the compressive overload on the crack growth rate was found. With the increasing tensile overload ratio, the crack closure effect exhibited increase. Tensile overloads also enlarge the crack deflection and produced more secondary cracks in the overload-affected zone of the crack-tip. The possible reasons for the overload-dependent crack growth behavior of Ti-6Al-4V ELI alloy were further analyzed in terms of microstructure, crack closure and crack-tip plastic zone.