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

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 gamma-Al2O3 and theta-Al2O3, two dominant metastable phases before transforming to stable alpha-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 gamma-Al2O3 (0 0 1)/NiAl (1 0 0) interface, the presence of interfacial Al vacancies in gamma-Al2O3 drives the interfacial segregation and aggregation of Hf atoms from the NiAl substrate, resulting in interfacial nucleation of HfO2. By contrast, for the theta-Al2O3 (1 0 0)/NiAl (1 0 0) 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 theta-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.

Automated summary

This study elucidates the interfacial dynamics of hafnium with gamma-Al2O3 and theta-Al2O3 during the oxidation of Ni-Al alloys. The presence of interfacial Al vacancies plays a critical role in influencing the interfacial segregation of Hf atoms and HfO2 formation. The results provide insights into manipulating the interfacial transport process of reactive elements by controlling the phase and stoichiometry of the transient oxide phases.