Influence of grit blasting pre-treatment on the adhesion strength of plasma sprayed coatings: fractal analysis of roughness

Since the adhesive strength of ceramic coatings by plasma spraying is fairly low, serious efforts have been made to improve it. In order to improve the adhesiveness of coatings, the substrate surfaces were roughened by blasting, sometimes by angled blasting as a pre-treatment. The measured adhesive strength showed the maximum value at blasting angle 75 degrees. Average surface roughness of the substrates remains almost constant with respect to the blasting angle. Introducing fractal analysis to evaluating the surface topography of substrates, the fractal dimension was evaluated for the roughened surfaces. It showed a maximum fractal dimension at 75 degrees where the adhesive strength reaches approximately its maximum value. It is concluded that fractal dimension is a better measure than average surface roughness for the evaluation of adhesive strength of ceramic coatings. (C) 1998 Elsevier Science S.A.