The influence of the heating procedure on the oxidation behaviour of NiAl studied by XPS

The initial stages of oxidation of NiAl at 870 K have been investigated with emphasis on the influence of the sample heating procedure. The compositions of the oxide films were analysed by XPS. The results show that if the NiAl is brought to temperature in vacuum before admission of oxygen, scales of pure alumina develop. On the other hand, if the material is pre-oxidised at 670 K for a few minutes, a film rich in NiAl 2O 4 forms; subsequent oxidation at the higher temperature then produces not a pure alumina scale but one still rich in the aluminate. It seems, therefore, that if the initially formed scale, which is to form the starting point for the controlled growth of a textured alumina microstructure, is to avoid the inclusion of Ni oxides, it should be grown on a vacuum heated surface. This may be a possible alternative to the traditional rapid heating procedures.