A general approach to controlling and modelling friction and wear in sliding contacts with coated surfaces is presented. The tribological aspects of the main material parameters, elasticity, plasticity and fracture are discussed. The contact condition with a rigid sphere sliding over a steel plate coated with a very thin hard coating is analyzed. The dominant parameters for friction and wear performance are identified and the appropriate material parameters needed for controlling the tribological contact is proposed. A Three Dimensional Finite Element Method (3D FEM) model has been developed for calculating both the first principal stress distribution and real stress components in the scratch tester contact of a diamond spherical tip moving with increased load on a titanium nitride (TiN) coated steel surface. The three dimensional model is comprehensive in that sense that it considers elastic, plastic and fracture behaviour of the contacting surfaces. Three main regions of stress concentration during the scratching action are identified and shown by simulated stress animations. The loading mechanisms and the stress development in each of these regions are described. The first cracks to occur on the surface of a steel plate coated with a 2 micrometer thick TiN coating sliding against a spherical diamond tip are shown. They are in an angular direction to the formed contact groove at the side edge of the groove due to the two directional high stresses in the side-stress region. This corresponds to empirical observations. By identifying from a scratch experiment the location of the first crack and using this as input data can the fracture toughness of the coating be determined. The influence of the coating thickness and elastic modulus on the stresses and strains generated during the sliding process is demonstrated.

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