Models for hardness and adhesion of coatings

Abstract

Indentation tests are widely used because they are apparently very simple to interpret in terms of mechanical properties. In the special case of coatings, indentation tests may be performed in order to determine hardness (even when the substrate interferes in the measurement) or adhesion properties, as long as some problems of interpretation are solved. In the first part of the paper, it is shown that existing models are not satisfactory for predicting hardness and instead a new model is presented based on the plastic deformation volumes under the indenter. The second part of the paper examines how the indentation is capable of creating and propagating a crack at the interface between the coating and the substrate, and the applied load–crack relation is interpreted in terms of an apparent interfacial toughness which can be correlated with adhesion.