A novel approach to investigate oxidation behaviour and mechanical properties of CVD bilayer TiN/TiC coatings

Abstract

A novel approach to investigate the oxidation behaviour of bilayer TiN/TiC coatings deposited on WC-Co substrate by CVD method was employed. Two coatings with different structures and mechanical properties were manufactured using different processing parameters. Energy dispersive X-ray analysis was utilized to monitor the elemental composition during oxidation tests at 800 ?C for up to 40min, which simulated the high temperature conditions experienced by the coated cutting tools. The obtained results demonstrated that the oxygen content increased significantly, reached ~68.8 at.%, while carbon and nitrogen contents decreased due to the formation of gaseous by-products. X-ray diffraction confirmed complete transformation of the TiN layer into rutile-TiO2 after 20min of oxidation. The microhardness of the coated samples significantly decreased due to the oxide formation and development of pores and cracks during the oxidation process. Tribological tests revealed a significant increase in the volume loss during dry sliding against zirconia counterpart after 20min of oxidation time. Moreover, surface colour of the oxidized coated samples changed from silver-white to grey-black with oxidation progression, enabling visual evaluation of oxidation damage.