First-principles study on the NiAl/Al2O3 interfacial segregation of Hf during the oxidation of Hf-modified NiAl

Abstract

Despite the well-known beneficial effect of reactive element dopants on improving the oxidation resistance of alumina-forming alloys, many open questions remain, including the migration and segregation of reactive elements at the oxide/alloy interface, a key zone in controlling the global oxidation kinetics and interface adhesion. Herein, we elucidate the atomic processes governing the interfacial dynamics of hafnium with γ-Al2O3 and θ-Al2O3, two dominant metastable phases before transforming to stable α-Al2O3 during the oxidation of Ni-Al alloys. Our results show that Al vacancies in the Al2O3 overlayer play a critical role in influencing the interfacial segregation of Hf atoms and HfO2 formation. For the γ-Al2O3 (001)/NiAl (100) interface, the presence of interfacial Al vacancies in γ-Al2O3 drives the interfacial segregation and aggregation of Hf atoms from the NiAl substrate, resulting in interfacial nucleation of HfO2. By contrast, for the θ-Al2O3 (100)/NiAl (100) interface, the presence of interfacial Al vacancies steers the migration of Hf atoms from the NiAl substrate across the oxide/alloy interface deeper into the oxide lattice, promoting the HfO2 formation in the bulk of the θ-Al2O3 layer. These results may find broader applicability for manipulating the interfacial transport process of reactive elements by controlling the phase and stoichiometry of the transient oxide phases.