AES INVESTIGATIONS OF PLASMA-SPRAYED AL2O3 COATINGS ON NI

The system of plasma sprayed Al2O3 on Ni substrates is investigated by means of AES/depth profiling. The influence of two process parameters - preoxidation procedure and spraying temperature - is examined. Rupture between substrate and ceramic layer occurs between a residual - or, in the case of excessive preoxidation, a superfluous - NiO layer on Ni, the thickness of the former depending on preoxidation conditions and the Al2O3 layer, the back side of which being partially covered with NiO. The thickness of this NiO layer increases up to about 1 mum with the thickness of the initial NiO layer on the substrate, until this layer is about 1.3 mum thick, and remains constant thereafter. The same dependence is observed for the width (0.1-1 mum range) of the mixed oxide interface between the sprayed Al2O3 layer and the NiO layer below. These results represent the chemical contribution to adherence. Contrary to excessive preoxidation, an increase of the spraying temperature from 300-degrees-C to 500-degrees-C effects broader interfaces.