Influence of frequency and C2H2 flow on growth properties of diamond-like carbon coatings with AlCrSi co-doping deposited using a reactive high power impulse magnetron sputtering

In this paper, diamond-like carbon (DLC) coatings with AlCrSi co-doping were deposited by a reactive high power impulse magnetron sputtering (HiPIMS) with utilizing a gas mixture of Ar and C2H2 as the precursor. The doping contents of Al, Cr and Si in the coatings were controlled by adjusting the C2H2 flow fraction in the gas mixture. The influences of the HiPIMS frequency and C2H2 flow on the microstructure, composition, mechanical properties and tribological behaviors of the AlCrSi-DLC coatings were researched carefully by using scanning electron microscope, X-ray photoelectron spectroscopy, nano-indentation and ball-on-plate tribometer, respectively. The results show that the doping AlCrSi contents increased as the C2H2 flow fraction decreased, along with the obvious structural transformation of the coatings from amorphous feature to carbide composites. The high C2H2 flow fraction tends to cause the target poisoning, resulting in the instability of the coating composition and the appearance of macro-droplets on the coating surface. The high pulse repeating frequency can effectively prevent the poisoning of the metal target and avoid the form of the arcing even at high C2H2 fraction, which is conducive to control the doping contents of the metal atoms and improve the surface quality of the AlCrSi-DLC coatings. In addition, the high frequency can facilitate the formation of the carbide, which has been expected to improve the hardness of the coatings. However, the existence of a mass of carbide phase causes serious abrasive wear of the coatings at low C2H2 fraction.