Adhesion of the γ-Ni(Al)/α-Al2O3 interface: a first-principles assessment

Abstract

Abstract We assess density functional theory studies of the effects of interfacial stoichiometry, Al activity, S segregation and Hf doping on the adhesion of the γ-Ni(Al)/α-Al2O3 interface. Computations of the Al activity in γ-Ni(Al) and of the interfacial phase diagram between 1300 and 1600 K suggest that the interface phase is Al-rich, but close to the boundary with the stoichiometric phase. We reveal that the Al-rich phase has significantly stronger adhesion than the stoichiometric phase and that S substantially decreases the adhesion of both. We demonstrate that doping with Hf yields a substantial improvement in adhesion, manifest in three ways: (i) It can pin S in bulk γ-Ni(Al), even up to 1600 K. (ii) It segregates and, once there, can strengthen the relatively weak stoichiometric interface (attaining a work of separation comparable to that for the strong Al-rich interface). (iii) It has the potential to displace S from interstitial interface sites.