Assessment of Residual Stress in Protective Coatings on PCBN Substrates

This study refines the calculation-experimental approach to evaluating residual stress in thin vacuum-plasma protective coatings on tools made of polycrystalline cubic boron nitride (PCBN), taking into account the thermal and structural components that arise during their formation. The stress values in a TiNbN coating were calculated using experimental data on the deformation of a model specimen—a thin steel plate—and the structural and thermally induced components of residual stress in the coating were identified. A functional relationship was found between the specimen deflection, coating deposition temperature, Young’s modulus, and residual stress in the coating. Using data obtained from model specimens, the residual stress was determined in a coating applied to a PCBN substrate of the Borsinit tool. The absolute values of the total residual stress significantly increased with coating thickness from 1 to 2.5 µm, reaching 1.9 GPa. The results demonstrate that the residual stress remains within safe limits regarding the potential cohesive failure of the coating.