Microstructural changes and elemental diffusion of sputtered NiCrAlY coating on a Ni-base SC superalloy subjected to high temperature

Microstructural changes and elemental diffusion of sputtered NiCrAlY coating on the Ni-base SC superalloy were investigated. Tests were conducted by exposing coated specimens both in vacuum and in still air at 1000 degrees C. XRD and SEM were used to analyze phases and microstructures. EPMA was used to characterize the distribution of elements in the coating interdiffusion layers and substrates. It was found that the as-sputtered NiCrAlY coating showed homogeneous element distribution with abrupt change of constituent at the interface between the substrate and the coating. After vacuum heat treatment, microstructural and phase changes occurred in the coating because of interdiffusion between the substrate and the coating-an interdiffusion layer and two new phases emerged. After 200 h oxidation at 1000 degrees C in air, the interdiffusion layer thickened and a diffusion influenced layer emerged below the interdiffusion layer in the substrate. Some of the Al in the gamma'-Ni3Al phase was replaced by Ta, resulting in an increase of the lattice parameter a(0) of gamma' phase. (C) 2007 Elsevier B.V. All rights reserved.