Chemistry and bonding investigations of NiAl/gamma-Al2O3 interfaces

An external oxide film is formed on the surface of NIAl as a result of high-temperature oxidation in air. By conventional transmission electron microscopy and diffraction the oxide film was found to be gamma-Al2O3. The relative orientation relationship between the oxide film and underlying substrate is: [100]NiAl parallel to [110]gamma-Al2O3 and (001)NiAl parallel to (001)gamma-Al2O3. Facets formed along (011)NiAl. Both the facets along (011)NiAl and the natural (001)NiAl oxide interfaces were examined with electron energy loss spectroscopy (EELS). The electron energy loss near-edge structure (ELNES) of Ni L and O K edges were examined. From the changes observed, the terminating plane is determined for both interfacial geometries. For the (001)NiAl/(004)gamma-Al2O3 interfaces, the oxide planes consist of both Al and O atoms, whereas the metal could be either Ni or Al terminating. Both the O K and Ni L ELNES supported the theory that aluminium is the terminating plane in the metal. For the (<01(1)over bar)NiAl/(004)gamma-Al2O3 interfaces the metal planes consist of Ni and Al atoms, whereas the oxide planes could be Al or O terminating. Again, the O K and Ni L ELNES supported the theory that the terminating plane in the oxide is aluminium.