Hardness of coatings

TLDR: In this article, the authors compare the predictions obtained using different models and to understand why it is often reported that the Jonsson and Hogmark model does not hold for indentation prints less than the coating thickness.

Abstract: The extensive use of appropriate coatings to improve wear resistance, friction coefficient, electrical properties and protection from corrosion has stimulated a growing interest in their mechanical properties, and especially hardness measurements. The objects of this study are to compare the predictions obtained using different models and to understand why it is often reported that the Jonsson and Hogmark model does not hold for indentation prints less than the coating thickness. Methods were reviewed for calculating the composite hardness, and it was found that the simplifications made by the authors are not always valid. By taking in account all the terms of the equations of Jonsson and Hogmark, it was found that the relation between the hardness and the reciprocal length of the indentation print is not linear and depends on the ratio between the film thickness and the indentation print, as well as the variation of the hardness of the substrate and the film with the applied load. Comparison of the Burnett and Rickerby experimental data with the modified model led to very good agreement.