Interfacial oxidation of hafnium modified NiAl alloys

Abstract The high-temperature oxidation of Hf-modified NiAl alloy at 950 °C results in the formation of γ-Al2O3 and θ-Al2O3. Exclusive formation of HfO2 particles is observed at the adherent γ-Al2O3/NiAl interface. By contrast, the θ-Al2O3/NiAl interface oxidation results in multi-layered oxide growth consisting of alternate thin and thick layers of θ-Al2O3 and NiAl2O4 along with dispersed HfO2 particles in the oxide layers. This difference is elucidated by first-principle calculations showing that the θ-Al2O3 lattice is more favorable than γ-Al2O3 to host Hf and Ni atoms, thereby resulting in the growth of mixed oxides at the θ-Al2O3/NiAl interface.