Effect of aging on fatigue-crack growth behavior of a high-temperature titanium alloy

Abstract

The effects of aging on the room-temperature fatigue-crack growth (FCG) behavior of a newly developed high-temperature near-a titanium alloy (Ti-5.6Al-4.8Sn-2Zr-l.0Mo-0.32Si-0.8Nd) with both bimodal and lamellar microstructures were investigated. The results indicate that aging had a relatively small effect on the FCG behaviors of the concerned alloy. The effect of aging is more pronounced on the lamellar than on the bimodal microstructure. This effect reduces with aging time especially for the lamellar microstructure. TEM and SEM studies were performed to gain insight into the deformation behavior and crack propagation mechanisms of the alloy. Dependence of the FCG rates on aging treatment is rationalized by considering changes in crack path tortuosity, roughness-induced crack closure and deformation uniformity. Slip reversibility is also considered. The work suggests that the amount and size of α2 particles based on TisAl is mainly responsible for this dependence in the high ΔK range.