INTERDIFFUSION BEHAVIOR IN ALUMINIDE-COATED RENE 80H AT 1150-DEGREES-C

The hot-section components in commercial aero gas turbines are typical ly made of a nickel-base superalloy and are protected by a diffusion-a luminide coating. At elevated temperatures this alloy/coating system i s metastable and, as a consequence, microstructural changes occur. The extent to which these changes occur is critically dependent upon temp erature and time. In the case of overheating, where the component temp erature exceeds about 1100 degrees C, the microstructural changes are often extensive enough to cause a decrease in both the strength and pr otectiveness of the alloy/coating system in a relatively short period of time. This paper reports the effects of overheating on the microstr uctural changes that occur in an aluminide-coated; nickel-base superal loy, Rene 80H. The overheating condition was simulated by isothermally heating at 1150 degrees C for up to 167 h. Both the alloy/coating int erdiffusion kinetics and the time-dependent phase changes resulting fr om interdiffusion are discussed. The interdiffusion behaviour is compl ex and requires the application of diffusion paths for proper interpre tation. (C) 1997 Elsevier Science S.A.