Postprint version. Published in Scripta Materialia, Volume 43, Issue 7, September 15, 2000, pages 631-636.
NOTE: At the time of publication, the author Trevor Harding was not yet affiliated with Cal Poly.
The definitive version is available at https://doi.org/10.1016/S1359-6462(00)00471-1.
High cycle fatigue has become the leading cause of failure in gas turbine engine blades in recent years . 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 and 4]. However, impacts of more brittle materials, such as γ-TiAl, would likely result in the formation of cracks. Steif et al  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 γ-TiAl alloy were examined by Lerch et al . 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 γ-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 γ-TiAl to industrially relevant gas turbine engine applications.
Materials Science and Engineering
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