Structural and tribomechanical properties of Cr-DLC films deposited by reactive high power impulse magnetron sputtering

Abstract

Hydrogenated Cr-containing diamond-like carbon (Cr-DLC) films were deposited onto silicon and Ti-6Al-4V (TC4) alloy substrates using high power impulse magnetron sputtering (HiPIMS) technology with various bias voltages. A comprehensive investigation was conducted to analyze the element composition, surface morphologies and roughness, chemical bonding states as well as the mechanical and tribological properties of films. The results revealed a slight increase in the Cr content in films, ranging from 7.7 at. % to 11.2 at. %, as the bias voltage was raised from −80 V to −200 V. Surface particles on films were significantly diminished at moderate bias voltage. Moreover, the fluctuation in surface roughness exhibited a similar trend to the surface morphologies, reaching 236.9 nm at −80 V, then decreasing to 57.8 nm at −150 V. However, upon further increase to −200 V, the surface roughness inversely rose to 121.9 nm. This phenomenon can be attributed to the etching effect resulting from the bombardment of high-energy ions. The Cr atoms in films predominantly existed in the form of Cr-C bonds independent of bias voltage. The hardness results of the films demonstrated the highest value of 15.1 GPa at −150 V, which then decreased to 8.3 GPa at −200 V, influenced by the transformation of sp3-C to sp2-C bonds due to the high-energy ions bombarded at high bias voltages. Tribological findings indicated that the coefficient of friction (COFs) of films remained largely unaffected by the bias voltage under 5 N normal load, varying between 0.10 and 0.15, the maximum wear rate of film was 6.06 × 10−7 mm3/N⋅m. Nevertheless, all films showed decreased COFs and wear rates with an increase in load. These research findings hold promise for enhancing the practical engineering applications of DLC film in the field of surface modification for titanium alloys.