Interfacial oxidation of hafnium modified NiAl alloys

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.