Tribological properties of nanocomposite Cr-Mo-Si-N coatings at elevated temperature through silicon content modification

CrMoN coatings has been found to have superior mechanical and tribological properties, such as high hardness, low friction due to the solid solution strengthening and the formation of lubricating molybdenum oxide. In this study, the mechanical and tribological properties of CrMoN with various Si contents were investigated. With Si contents ranged from 0 at.% to 11.1 at.%, the quaternary Cr-Mo-Si-N coatings were deposited on silicon wafer and Inconel 718 by RF magnetron sputter. Through nanoindentation, the hardness and the H3/E⁎2 ratio of Cr-Mo-Si-N coatings were obtained. The results showed that mechanical characteristics in Cr-Mo-Si-N coatings were strongly influenced by Si contents. The Cr-Mo-Si-N coating exhibited highest values in hardness and H3/E⁎2 ratio with 7.5 at.% Si doped, in which columnar grains turned into nanocomposite structure. The strengthening mechanism of nanocomposite structure was attributed to grain refinement and prevention of direct penetration of cracks. Futhermore, tribological behavior of Cr-Mo-Si-N coatings was investigated by ball-on-disc tribometer in atmosphere at 750 °C and 800 °C. The results indicated that the tribological properties of Cr-Mo-Si-N coatings at 750 °C could be significantly improved with the Si addition due to protective oxide formation on wear tracks and the cooperation of MoO3 as solid lubricant. At 800 °C, the liquidus MoO3 formed and played an important part in the decline of friction coefficient as compared to that of 750 °C. At the elevated temperature, MoO3 contributed to low friction coefficient, while the low wear rate was owing to the presence of anti-wear oxide and the nanocomposite structure. With 7.5 at.% Si doping, the Cr-Mo-Si-N coatings showed superior mechanical and tribological characteristics, leading to potential applications for wearproof and self-lubricating dry cutting tools at elevated temperature.