Comparison of chromium carbide thin films grown by different power supply systems

The potential use of chromium carbide thin films has been a great interest to academia and industry due to their outstanding properties such as chemical stability, low coefficient of friction, adequate hardness and high wear resistance. In this study, the chromium carbide thin films were fabricated by a magnetron sputtering using different power supply systems, including direct-current (DC), pure high power impulse magnetron sputtering (HiPIMS), and superimposed HiPIMS- middle frequency (MF). The Cr target poisoning status was controlled using a plasma emission monitoring (PEM) system by adjusting the gas flow ratios of Ar and acetylene (C2H2). The morphology and microstructure of thin films were evaluated by scanning electron microscope (SEM) and transmission electron microscope (TEM). The crystallinity of films was studied using an X-ray diffractometer (XRD). The electron probe micro analyzer (EPMA) and X-ray photoelectron spectroscope were used to determine the chemical compositions and binding structures of thin films, respectively. The hardness and residual stress were explored. The results showed that the thin film sample prepared by the superimposed HiPIMS-MF power supply can obtain the maximum hardness of ~27.5 GPa at a PEM set point of 30%, i.e., the target poisoning degree of 70%. The hardening mechanism may be caused by the formation of nanoscale CrC crystallites incorporated into the amorphous CrCx matrix in the thin film, which can be attributed to the Hall-Petch strengthening effect.