Wear resistance optimisation of composite coatings by computational microstructural modelling

The wear resistance of components can be changed remarkably by surface coatings. New processing methods offer many possibilities to tailor the wear resistance of surfaces to match design criteria. Computational modelling and simulation is a systematic approach to optimise the wear performance. Modelling of physical surface phenomena can be carried out on all spatial scale levels, from sub-atomic one to macrolevel and for the various stages in material development, from material processing to structures, properties and performance. The interactions between the coating matrix, the reinforced particles, degraded material phases and defects like pores, cracks and voids are of crucial importance for the wear performance of composite coatings. This has been modelled by synthetic artificial models to find general design rules and by real image based models to find out the wear behaviour of specific coatings. The effect of particle size, morphology, clusters, mean free path and porosity was simulated for thermal spray WC-CoCr coatings. Four main very typical mechanisms for crack initiation resulting in surface failure have been identified: brittle carbide fracture, ductile binder cracking, interface failure, and cracking from pre-existing porosities and defects. The most important coating properties having a crucial effect on coating wear resistance are defects in the coating structure as they can create detrimental stress peaks and high strain levels, particle clustering is most critical for the durability of the structure, the elasticity of the particle is of great importance as well as matrix hardness and particle morphology