Effect of cathodic arc plasma treatment on the properties of WC–Co based hard metals

In this study, ion bombardment in a cathodic arc physical vapor deposition system was applied on WC–Co hard metal surfaces aiming to benefit from the diffusion acceleration effect, and to investigate the role of this effect on the surface composition, morphology and corrosion resistance of the materials. Chromium ions obtained via cathodic arc evaporation were accelerated under low (−150V) and high (−1000V) bias voltages in order to apply coating–bombardment cycles to sample surfaces. Substrate temperatures were measured by an optical pyrometer during the processes. The treated samples were characterized by scanning electron microscopy (SEM) and X-ray diffractometry (XRD). Temperature measurements showed that the sample temperature could be controlled precisely by adjusting the bias voltage. Temperatures in the range of 750–1200°C were measured during the treatment depending on the duration of the high bias voltage cycles. XRD analysis showed η phase formation in the near surface regions of all treated samples. The amount of the formed η phase was shown to be dependent on the heating–cooling regime that varied with the applied mode of bias. The corrosion behavior of the samples was investigated by immersing treated and untreated samples in a solution of 5% H3PO4 containing 1g/l Zn+2 for 24h at 50°C. The samples were investigated via SEM observations after immersion. Cathodic arc plasma treated samples showed a better resistance to corrosion in this environment.