Finite element analysis of damage properties in scratch test of TiN/WC-Co coating cutting tool

The stress distribution of the coating/substrate system during the scratch test is one of the most important parameters that control the behavior and failure modes of the coating/substrate system. Because of the complicated loading conditions, friction between the indenter and the coating, as well as the nonlinear elastic-plastic behavior of the coating and substrate, it is very difficult to obtain numerically and experimentally the stress distributions inside the coating, especially, at the coating/substrate interface. Attempts at theoretical modeling of these phenomena lead to highly non-linear models, which can be solved only numerically. TiN is one of the most ideal cutting tools coating materials. TiN coating can reduce the cutting edge material attachment and the cutting force, increase feed, improve processing accuracy, maintain cutting geometry stability and improve the surface quality of workpiece. The damage process of the scratch test of TiN/WC-Co coating cutting tool was simulated by finite element method. The stress distribution of the coating/substrate system during the scratch test was analyzed. The interface damage and the whole damage of TiN/WC-Co were simulated. The interface strength was defined by comparing the simulation results with the scratch test results. In the scratch test of TiN/WC-Co, the damage began and expanded from the surface behind the indenter. Transverse cracks occurred in the coating surface. Then the interfacial delamination occurred between the coating and the substrate. The maximum tensile stress was the main reason to cause coating cracking. And the interface shear stress was the main reason to cause coating delamination and substrate damage. In the scratch test, the coating/substrate system was loaded on normal force and tangential displacement. It was found that the damage of the coating occurred mainly behind the indenter, but the damage of the interface and substrate occurred mainly ahead the indenter. But there was no damage under the indenter. It may be concluded that scratch tests can be simulated effectively by taking into account of the interface damage, coating damage and substrate damage. Some important results could be obtained such as the interface strength, the damage occurring and developing, the damage modes, etc.