Out-of-Phase Thermomechanical Fatigue Behavior of a NiCrAlYSi-Coated Superalloy

Arc ion plating was employed on a directionally solidified nickel-based superalloy to deposit a NiCrAlYSi coating. The failure behavior of the coated cylindrically specimens under thermomechanical fatigue loadings was experimentally investigated. The results show that the effect of coatings on TMF lives is dependent on the temperature ranges, and the TMF life with dwell time is reduced compared to the one without dwells. Through microstructure observation methods, the Al-rich areas in the coatings especially near the interfaces of the coating and superalloy are crack initiation sites. The combination of temperature dependent localized oxidation and stress concentration at the crack tip dominate the crack initiation and small crack propagation procedure.