High temperature fatigue properties of Micro Spark Coated Ni-based superalloy

Abstract

High temperature fatigue properties of the Inconel 718 superalloy specimens to which a Co-based wear resisting alloy, Stellite 31, was coated by the Micro Spark Coating (MSC) method, were investigated as well as the microstructural stability. It was shown that the microstructure of the coating was almost stable even after the long term isothermal aging at 480°C by 1 000 h in air, while it changed significantly at 650°C. In the latter, increase in hardness was seen, associated with an evolution of oxide rich phases. The fatigue properties of the coated specimens revealed a complex behavior depending on the loading level and test temperature : in high cycle regime the coated specimens showed shorter fatigue lives than the Inconel 718 substrate, while the former longer than the latter in low cycle regime. It was suggested that high temperature fatigue properties were influenced by two phenomena : one was the prior substrate surface characterization that might be affected by MSC process; and the other was a load transfer capability of the coated area, depending on the test temperature and exposure time.