The repeated spherical indentation test: an efficient way to evaluate the adhesion of hard coatings

Fatigue failure of hard coatings usually occurs at much lower loads than failure under static loading. Hence one way to evaluate coating adhesion should be cyclic loading close to service conditions. In this study, a new method of adhesion measurement for hard coatings is introduced based on interfacial fatigue under repeated indentation. Mono- and multi-layered coatings with different interfacial states are evaluated by a repeated-indentation test. Detachment of the coatings occurs initially at the rim of the indenter imprint, apparently as a result of adhesive failure. In contrast to monolayer coatings, peeling of multilayer coatings depends on the lowest strength of the interfaces. This study also demonstrates that the adhesion determined by the repeated-indentation test is sensitive to the interfacial state, allowing an optimised or weakened interface to be clearly revealed.