Fundamentals of adhesion of thermal spray coatings: Adhesion of single splats

Indentation experiments were performed inside a scanning electron microscope to measure adhesive strength of individual alumina splats on a steel substrate. The in situ nature of experimental evaluations made characterization of interfacial crack propagation possible by direct observation. The increase in the strain energy of brittle alumina splats originating from indentation deformation was correlated to the strain energy release rate through the characterization of interfacial crack propagation. An analytical model previously reported and evaluated in studies of the adhesive strength of thin films was employed. An average calculated strain energy release rate of 80 J m−2 was found for single splats. This high value suggests that splat adhesion can make a significant contribution to the adhesion of thermal sprayed coatings.