A geometrical model to predict the wear evolution of coated surfaces

The improvement of the thin films production techniques leads to the availability of a wide range of coatings with high mechanical properties difficult to be reached with monolithic materials. Thin coated surfaces reveal promising results in several applications, especially where high wear resistance is required. However, selecting the best solution for an envisaged application is a difficult task because the tribological performance depends on both coating and substrate properties and also on adhesion between the coating and the substrate. Therefore, among the main challenges of the surface engineering are included suitable procedures to assure enough adhesion between the coating and the substrate and calculation methods to predict the wear and the mechanical behaviour of each coating + substrate arrangement. Ball-cratering micro-scale abrasion technique solve partially this problem once it allows to determine the specific wear rates of coating and substrate by only one set of tests done with the coated surfaces. In this paper, prediction models based on the micro-scale abrasion tests, will be presented and discussed. The derived geometrical models allow the study of ball-on-plane contact and also of crossed-cylinders contact. The ability of these models to be applied on coating development was demonstrated applying the prediction criteria to study the effect of coating thickness and the coating intrinsic specific wear rate. The wear evolution forecasted by the model was also compared to experimental results of hard chromium plated steel and very good correlations were reached.