Influence of Microstructure on Residual Thermal Stresses in TiCxN1-x and α-Al2O3 Coatings on WC-Co Tool Inserts

The microstructures of chemical vapor deposited coatings on four tool inserts have been comprehensively characterized using electron backscatter diffraction mapping and these data have been used as input for finite element models used to calculate the residual thermal strains in the coatings. The results indicate that the thermal strains and stored elastic energy in the α-Al2O3 layer are larger than in the TiCxN1-x layer. Furthermore, the mean value and distribution of stored elastic energy are influenced by the texture in the alumina layer. Coatings with weaker texture have a broader distribution of thermal stresses. Coatings with alumina oriented so that the [0001] direction is parallel to the film growth direction have less stored elastic energy. This is because the thermal expansion perpendicular to [0001] is less than the thermal expansion parallel to [0001] and, therefore, the thermal expansion mismatch between the alumina coating and the substrate is minimized when grains are oriented with [0001] perpendicular to the substrate.