Tribo-mechanical properties of CrC/a-C thin films sequentially deposited by HiPIMS and mfMS

A sequence of high power impulse magnetron sputtering (HiPIMS) and mid-frequency magnetron sputtering (mfMS) was carried out to deposit a chromium carbide (CrC) interlayer and an amorphous carbon (a-C) top layer. The deposition of the interlayer by HiPIMS results in a higher adhesion strength and hence affects the properties of the a-C layer. The mechanical and tribological properties of a group of CrC/a-C films consisting of CrC with growing C content are investigated. In this context, single CrC and CrC/a-C films were systematically analyzed in order to evaluate the influence of the CrC interlayer on the properties of CrC/a-C. A higher amount of C changes the morphology of CrC films from a columnar to fully dense microstructure. The hardness decreases from 13.8 to 12.3 GPa with a growing C content, but the H/E- and H-3/E-2-ratios increase to 0.073 and 0.068 GPa, respectively. In contrast to the CrC interlayers, the CrC/a-C film systems.are marked by a higher hardness of up to 19.8 GPa. The H/E- and H-3/E-2-ratios are also significantly higher with values of 0.090 and 0.155 GPa when compared to the CrC single films. The CrC layers exhibit the best adhesion class HF1 in Rockwell tests and a maximum critical load L-c3 of 41 N in scratch tests. The adhesion strength of CrC/a-C is strongly affected by the CrC interlayers; as generally similar failure mechanisms are observed for both film systems. The friction behavior of the CrC/a-C films is only influenced by the a-C top layer. The high adhesion strength of CrC prevents delamination failures when tribologically loading CrC/a-C films.