Effects of segregating elements on the adhesive strength and structure of the α-Al2O3/β-NiAl interface

We investigate with first-principles density functional theory (DFT) the adhesion of the Al2O3(0001)/NiAl(110) interface as a model for the thermally grown oxide/bond coat alloy interface in thermal barrier coatings. We find that the clean interface has an ideal work of adhesion of 0.66 J m(-2). We predict that S impurities reduce interfacial adhesion significantly, due to a reduction in cross-interface bonds. The presence of Pt alters the interface adhesion only slightly, while Hf dopants dramatically increase adhesion via formation of strong Hf-O bonds, as expected from Hf's open-shell character. We discuss the implications of these predictions, which are consistent with experimental observations of the effects of S, Pt, and Hf on the lifetime of thermal barrier coatings. (C) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.