Nanoindentation studies of thin film coated systems

In this paper we report the results of ultralow load indentation (“nanoindentation”) tests carried out on a range of thin film coated systems. In addition to characterizing the properties of each system at high resolutions, a further principal aim has been to explore the extent to which it is possible to generalize the nanoindentation response of the various systems in terms of the relative mechanical properties of the coating and the substrate. In this case we classify the substrate and coating in terms of the relative elastic and plastic responses (i.e. the ratio of yield stress to Young's modulus). Some of the different possible responses are shown together with the transitions in response (elasticity-dominated to plasticity-dominated and vice versa) which can occur. We also report on the various steps which can occur in loading curves and our attempts to relate them, via high resolution scanning electron microscopy, to the fracture patterns (through-thickness cracks and interfacial cracks) within and around the indentations.