Effect of some thermal treatments on interface adhesion toughness of various thick thermal spray coatings

Interfacial indentation is used to create and propagate a crack in the interface plane between a coating and its substrate. It has been shown earlier that this methodology allows the measurement of an apparent interface toughness, which can represent the adhesion of the coating to its substrate. In service thermal spray coatings are subjected to various external influences, which could be detrimental to their adhesion, e.g. thermal shock, fatigue, wear, corrosion and combinations of these. The objective of the present work is to study some of these effects and their influence on the interface adhesion toughness of various substrate/coating systems based on new phenomenological approaches to the residual stress state existing in the coating: (a) annealing treatment – for as sprayed specimen, it was first shown that the interface toughness is directly proportional to the reciprocal of the squared coating thickness. Extrapolated to an infinite thickness, the toughness could be assumed then to repres...