Effect of the bias-graded increment on the tribological and electrochemical corrosion properties of DLC films

Abstract

Diamond-like carbon (DLC) films with bias-graded increments of 5 V, 10 V, and 20 V were prepared by adjusting the substrate bias voltage in a high-power pulsed magnetron sputtering system (HPPMS). The microstructural, mechanical, tribological, and electrochemical corrosion properties of DLC films were systematically investigated. In this work, the sp 3 content in the DLC film with a constant bias of −200 V was the highest, and the sp 3 content in the bias-graded DLC film exhibited a gradient increasing trend. Bias-graded DLC films had lower hardness, elastic modulus and residual stress than DLC film with a constant bias of −200 V. With a decrease in bias-graded increment, the ratio of hardness to elastic modulus increased. Friction and wear tests demonstrated that the wear resistance of the DLC film was related to the hardness, residual stress and ratio of the hardness to the elastic modulus. The wear rate decreased with decreasing bias-graded increment, and the DLC film with a bias-graded increment of 5 V had the lowest friction coefficient and wear rate, which were 0.077 and 6.74 × 10 −7 mm 3 /Nm, respectively. The polarization curve results revealed that the DLC film with constant bias had the highest corrosion potential and corrosion current density. As the bias-graded increment increased, the corrosion potential and corrosion current density showed an increasing trend. Combined with the electrochemical impedance spectroscopy results, the bias-graded DLC films with bias-graded increments of 5 V and 10 V exhibited better corrosion resistances. • Bias-graded DLC films were prepared in HPPMS system. • Gradient structure achieved the balance between the residual stress and the content of sp 3 . • Coating DLC film can significantly improve the tribological and electrochemical corrosion properties of the substrate.