THE EFFECT OF HIGH MODULUS SINGLE AND DOUBLE-LAYER COATINGS ON CONTACT STRESSES

The elastic stress distributions arising from spherical indentation of high modulus single and double layer coatings of different thicknesses on a lower modulus substrate are investigated using finite element methods. It was found that the shape of the pressure distribution under the indenter is approximately the same as the Hertzian pressure distribution except for the thickest coatings. As a consequence, maximum radial tensile stresses obtained from this study agreed with the results of Van der Zwaag and Field, and Van der Zwaag, Dear, and Field for the thinnest coatings. However, the stresses were different for the thicker coatings where the pressure distribution under the indenter differed from the parabolic distribution. An approximate map giving the interface location of the maximum radial tensile and shear stresses as a function of coating moduli and total coating thickness is presented. The map shows that increasing the total thickness or increasing the modulus of the top layer moves the maximum radial tensile stress from the layer interface to the surface and moves the maximum shear stress from the substrate surface to the layer interface. In addition, the effect of the single and double layer coatings on the load-penetration depth response and the load-contact radius response is not significant when compared to the response of the uncoated substrate.