The influence of residual thermal stresses on the mechanical properties of multilayer α-Al2O3/TiCxN1 − x coatings on WC/Co cutting tools

Orientation maps of the microstructures of four α-Al2O3 and TiCxN1 − x multilayer coatings on WC–Co cemented carbide tool bit inserts were used to create realistic models for finite element calculations of residual thermal stresses. The calculations show that channel cracks in the coatings relieve thermal stresses and that the amount of stress relieved increases with film thickness. The hardness and fracture toughness of the coatings, measured by nano-indentation, are inversely correlated to the calculated mean thermal stress, where the hardest sample has the smallest calculated mean thermal stress. The calculations also indicate that cracks spaced more closely than about 50 μm are not effective in further reducing residual stresses.