Influence of cutting tool coatings on the tribological phenomena at the tool–chip interface in orthogonal dry turning

Four complementary methods are used to qualify the performance of the tribological system “workmaterial-coated carbide cutting tool–chip”, with the purpose of reaching a better global understanding of the capability of coatings: chip formation mechanisms, cutting forces, interface temperature are deduced from experiments and correlated with previous heat flux measurements already published. The experiments have been applied on the characterization of the frictional behaviour of a reference coating such as TiN, and of more advanced coatings such as TiAlN and TiAlN + MoS2, deposited on a WC-Co carbide substrate during the machining of steels. Results show that the TiN and (Ti,Al)N + MoS2 coatings exhibit to the best tribological improvements compared to uncoated tools: important decrease of the tool–chip contact area, decrease of the thickness of the secondary shear zone and of the temperature at this interface, which lead to a decrease of the heat flux transmitted to the cutting tool substrate. The (Ti,Al)N coating exhibits an intermediate behaviour. Indeed, even if it improves somewhat some parameters such as the tool–chip contact length and the thickness of the secondary shear zone, the (Ti,Al)N coating does not enable a reduction of the interface temperature and has a limited influence on the heat flux transmitted to the substrate.