Interfacial Oxidation Of Hafnium Modified Nial Alloys

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