THE INFLUENCE OF PRETREATMENT ON THE ADHESION OF CERAMIC COATINGS ON STEEL

Pretreatment of the substrate in the form of grit blasting is shown to exert a critical effect on coating adhesion. The adhesion of plasma s prayed alumina coatings increases linearly with the average roughness of the substrate and reaches a maximum at an optimum peak spacing. The optimum spacing is found to increase with increasing particle size of the feedstock powder. The underlying mechanism of this behaviour is s hown to be related to the effect of the microgeometry of the substrate on the flow of the impacting molten particles. The optimum pretreatme nt provides a surface texture that suppresses splashing by dissipating the kinetic energy of the incoming droplets.