Interdiffusion behaviour in aluminide-coated René 80H at 1150°C

The hot-section components in commercial aero gas turbines are typically made of a nickel-base superalloy and are protected by a diffusion-aluminide coating. At elevated temperatures this alloy/coating system is metastable and, as a consequence, microstructural changes occur. The extent to which these changes occur is critically dependent upon temperature and time. In the case of overheating, where the component temperature exceeds about 1100°C, the microstructural changes are often extensive enough to cause a decrease in both the strength and protectiveness of the alloy/coating system in a relatively short period of time. This paper reports the effects of overheating on the microstructural changes that occur in an aluminide-coated, nickel-base superalloy, René 80H. The overheating condition was simulated by isothermally heating at 1150°C for up to 167 h. Both the alloy/coating interdiffusion kinetics and the time-dependent phase changes resulting from interdiffusion are discussed. The interdiffusion behaviour is complex and requires the application of diffusion paths for proper interpretation.