Diffusion and oxidation phenomena at elevated temperatures in the contact area between hardened steel and various PVD coatings

Growing cost reduction trends in machining applications has led to a significant increase of cutting speeds and process temperatures. In this way, oxidation and diffusion mechanisms in the contact area between chip and tool become substantial, affecting the tool performance.In this paper, diffusion and oxidation interactions at 800 °C among various PVD coated cemented carbide inserts, hardened steel counterparts and low oxygen atmosphere will be introduced. The experiments were conducted under adjustable ambient conditions by a device, developed for this purpose. The coated specimens were fastened inside an electrical heating unit in a controlled gas atmosphere, allowing their contact with steel specimens at a desired pressure and temperature. During the experiments, periodic intervals of the applied pressure were followed by brief non-contact pauses, to avoid any permanent welding between coating and counterpart. For providing insight on the effect of diffusion and oxidation on the films' chemical composition and mechanical properties, coatings' cross sections in the film contact area were investigated by EDX-line scanning. The results show a considerable deterioration of the films' mechanical properties, which can be attributed more to coatings' oxidation and less to diffusion.