A model for coated surface hardness

The authors present a model that predicts the hardness of a film deposited on the surface of a substrate. The model is based on a simple mathematical relationship involving the hardness of the film and the hardness of the substrate, together with the hardness of the composite film/substrate at a given film thickness/penetration depth ratio. The parameters of the present model depend on the mechanical properties of the film/substrate pair and can be experimentally determined by using depth-sensing hardness instruments. In the models found in the literature, the equation parameters are constants typical for each model. The present model is proposed and validated for the case of a film (W–C–Co coating) harder than the substrate (various metallic materials) and it allows determination of the film hardness without the need to determine either the film thickness or the substrate hardness.