Indentation tests on ceramic coatings are carried out in this paper and fracture pattern diagrams as a function of normal load and coating thickness are introduced for Al2O3 and TiN coatings deposited on cemented carbide substrates. Ring cracks are observed in indentation with a blunt indenter (1.5 mm radius), while lateral and radial cracks are observed in indentation with a sharp indenter (0.2 mm radius). The mechanisms for generating ring and lateral cracks are analyzed using elastic theory and equations predicting the critical loads for crack generation are introduced. The effective elastic modulus Eeff, is introduced for this analysis as a new elastic parameter for a coated surface. The results show that the theoretically calculated critical loads for crack generation agree well with the experimental ones.

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The local yield maps for the identification of the yield initiation positions of hard coating on three-dimensional (3D) elastic half space under sliding contact were developed. In this study, the semi-analytical method (SAM), which is based on the conjugate gradient method (CGM) and the discrete convolution and fast Fourier transform (DC-FFT) technique, was employed to analyze the contact problem. By using this method, the von Mises stress distributions for various combinations of coating thicknesses, friction coefficients, and elastic moduli of the coating and substrate were calculated. Then, the positions of yield initiation were found with the calculated results by comparing the critical maximum contact pressure P max,c for von Mises yielding at or in the different positions (surface, coating, interface, and substrate), and the 3D-local yield maps were introduced in relation to the yield strength ratio of the coating to the substrate (Y f /Y b ) and the ratio of the coating thickness to the Hertzian contact radius (t/a 0 ). Finally, the effect of critical friction coefficient on the transition of yielding positions was discussed.

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