Influence of intermetallic TiAl coatings on the fatigue properties of TIMETAL 1100

Fatigue properties of material are generally very prone to surface effects of various origins. Polished surfaces are known to have better fatigue performance than rough as-machined surfaces. Also compressive stresses in the surface are beneficial due to their crack closure capabilities at superimposed tensile loading. Exposure to oxidizing atmosphere drastically decreases fatigue strength of TIMETAL 1100 due to crack initiation in the embrittled surface layer. Therefore avoiding embrittlement of the surface by protective coatings is expected to improve the fatigue performance of the alloys. Prior investigations have shown the beneficial influence of gradient and multilayer coatings from the Ti-Al system on oxidation resistance, room temperature ductility and creep properties of TIMETAL 1100. In the present study, the influence of these coatings on the fatigue properties of TIMETAL 1100 exposed to air at 600 C will be discussed.