Modelling of the mechanical and tribological properties of coatings and surface treatments
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Modelling of the mechanical and tribological properties of coatings and surface treatments S.J. Bull School of Chemical Engineering and Advanced Materials University of Newcastle Newcastle upon Tyne NE1 7RU UK ABSTRACT Over the past few years a wide range of coatings and surface treatments have been developed to enhance component performance. Increasingly coating architectures are becoming more complex and multilayer, superlattice and graded coating systems are becoming widely available. This offers so many potential coating variants that it is almost impossible to envisage trying all the possibilities to optimise performance. The need for predictive performance models has never been more acute but model development has generally lagged behind the introduction of new coatings. For tribological coatings the mechanics of contact is particularly important if performance is to be understood. This paper briefly reviews developments in numerical simulation and extends recent modelling developments in an energy-based predictive model for the hardness and Young’s Modulus of a coated system. The model predictions can be improved by considering the fracture behaviour of the coating. INTRODUCTION The range of coatings and surface treatments developed for tribological applications continues to increase. However, whilst the development of new, higher specification layers has been rapid and widespread the development of methods for coating selection, optimisation and performance prediction is much less established. Workers have focused on improving the hardness, toughness and residual stress state of the layers, often using nanostructural or multilayered coating designs [1,2]. Whether hardness or fracture toughness are good indicators of tribological performance per se is a matter of debate, but hardness in particular is convenient to measure and is representative of some of the energy dissipation processes which do control wear behaviour. The role of modelling in all these areas is critical. A primary requisite of many applications is that neither the coating nor the substrate plastically deforms during a tribological contact (either at the bulk or asperity level) and this has been the subject of considerable contact mechanics research. A combination of finite element modelling, energy-based physical modelling and phenomenological modelling has been used to predict the onset of yield in a coating substrate system with some success. However, the best predictive models are always based on a requirement to determine some empirical parameters. Full elastic-plastic finite element modelling with realistic constitutive equations is rarely possible. As the situation becomes more complex, i.e. in sliding wear, empirical modelling becomes more dominant even if the models are physically-based. Therefore, there is a need for a hardness model that can be used to make predictions for a wide range of coating/substrate combinations with a few basic input parameters that are coating material and substrate specific. This paper outlines a
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