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. Rupt ure 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 a nd the Al2O3 layer, the back side of which being partially covered wit h NiO. The thickness of this NiO layer increases up to about 1 mum wit h the thickness of the initial NiO layer on the substrate, until this layer is about 1.3 mum thick, and remains constant thereafter. The sam e 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 belo w. These results represent the chemical contribution to adherence. Con trary to excessive preoxidation, an increase of the spraying temperatu re from 300-degrees-C to 500-degrees-C effects broader interfaces.