Postprint version. Published in Scripta Materialia, Volume 43, Issue 7, September 15, 2000, pages 631-636. Publisher website: http://www.elsevier.com. The definitive version is available online at: http://dx.doi.org/10.1016/S1359-6462(00)00471-1
NOTE: At the time of publication, the author Trevor Harding was not yet affiliated with Cal Poly.
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