On the determination of the film hardness in hard film/substrate composites using depth-sensing indentation

The main difficulty in the mechanical characterisation of thin films using depth-sensing indentation is the determination of the relative substrate and film contributions to the measured properties of the film/substrate composite. In this study, a three-dimensional numerical simulation of the Vickers hardness test is used to study the influence of the substrate and film mechanical properties on the composite's behaviour under depth-sensing indentation. The particular case of hard films on soft substrates is analysed. In order to understand the behaviour of the composite, a study of the plastic strain distribution under indentation of several composites is performed. A methodology to determine the relative film hardness, i.e. HF/HS ratio, is proposed. The methodology is successfully verified using fictitious and real composite materials.