Effect of the plasticity of the substrate on the performance of the coating on a tool

A new modelling procedure which combines parameterised FE modelling, Cohesive-Zone modelling and a sub-modelling technique has been developed to study the initiation and propagation of plastic deformation in the substrate material of a coated tool-steel (TiN coating on Nitrided 42CrMo4) and their effect on the failure of the coating due to fracture. The numerical results were then compared to experimental results obtained by micro-indentation with a spherical indenter. In the present study, cracking in the coating was observed with the advancement of the indenter, which was caused largely by plastic deformation in the substrate. During the indentation, plastic deformation was initiated in the substrate at the coating/substrate interface, and then propagated towards the contact-edge with the indenter. As the indenter progressed further, cracking was induced in the surface of the coating immediate outside of the contact-edge by the bending of the coating layer due to the load from the indenter and the sinking of the substrate. The work performed has led to new knowledge on the influence of the plastic deformation of the substrate material on the performance and failure of the coating-layer in a coated tool-steel