Effect of foreign object damage on the fatigue strength of an xd™ γ-TiAl alloy

Abstract

High cycle fatigue has become the leading cause of failure in gas turbine engine blades in recent years [1]. The majority of these failures were associated with surface damage such as foreign object damage (FOD). Therefore, the ability of a material to resist impact damage and the subsequent fatigue propagation of any cracks that may result has become a crucial design consideration. Substantial research has been conducted on the effects of simulated FOD in conventional turbine blade materials where the formation of cracks at the impact site was not a common occurrence [2,3,4]. However, impacts of more brittle materials, such as �-TiAl, would likely result in the formation of cracks. Steif et al [5] have examined the formation of cracks associated with impacts in several TiAl-based alloys. The effects of ballistic impacts on the fatigue behavior of a Ti-48Al-2Nb-2Cr �-TiAl alloy were examined by Lerch et al [6]. Fatigue strength was correlated with a somewhat arbitrary crack length with some success; however, no correlation with the long-crack fatigue threshold was made. The use of a fatigue threshold limit may be necessary for design of turbine blades given the limited fatigue crack growth resistance exhibited by �-TiAl. The present study investigates the reduction in elevated temperature fatigue strength of a Ti-46.8Al­ 2.1Nb-1.1Mn-0.1Si-1.4B alloy caused by simulated foreign object damage. This work is part of a larger effort to support the transition of �-TiAl to industrially relevant gas turbine engine applications.