Effect of silicon-doping on the wide-temperature tribological behavior and lubrication mechanism of WC/a-C film

Abstract

To expand the lubricating temperature range of a-C based film in air atmosphere, a novel Si and WC co-doping Si/WC/a-C film was proposed. The Si/WC/a-C film with different Si contents were prepared by an unbalanced magnetron sputtering system. The effects of Si on the microstructure, thermal stability and mechanical properties of WC/a-C films were explored, and its wide-temperature tribological behaviors against M50 steel were researched at temperatures ranging from 25 °C to 500 °C in air atmosphere. The Si-doping inhibited the crystallization of WC in films, leading to the microstructural transformation from nanocrystalline-amorphous to amorphous. The introduction of Si significantly improved the nanohardness, thermal stability and wide-temperature lubrication properties of WC/a-C film. Therein, the Si/WC/a-C film with 18.85 at.% Si exhibited the best tribological performance featuring the average friction coefficients less than 0.25 at 25–500 °C. Its prominent wide-temperature lubrication performance can be attributed to the successive generation and their combined effect of the self-lubricating phases of sp2-rich carbon, Si–O–C and WO3 in different temperature ranges. Remarkably, appropriate Si-doping can effectively inhibit the oxidation of sp2-rich carbon in tribological layers, thus it is the dominant lubrication phase throughout the wide temperature range of 25–500 °C.