Microstructural and microchemical development of simple and Pt-modified aluminide diffusion coatings during long term oxidation at 1050 °C

The microstructural and microchemical development of one simple (PWA73) and three Pt modified (RT22, SS82A and MDC150L) aluminide diffusion coatings under isothermal oxidation at 1050 °C for times ranging from 1000 to 20 000 h was studied by gravimetry, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Properties important for the useful life of the coating, such as: the gradual transformation of β-NiAl to γ′-Ni3Al, the interdiffusion with the substrate and the formation of internal voids are discussed in the light of the ability of the coating to maintain a protective oxide scale.