Enhancing the tribological property of Mo-doped DLC films in methanol using appropriate bias voltage

Abstract

Methanol is an ideal substitute fuel for oil resources, it has a wide application prospect in internal combustion engines. However, methanol has poor lubricity, resulting in increased frictional power consumption. In this study, Mo-doped diamond-like carbon (MoDLC) film deposition was performed using the magnetron sputtering method to enhance the tribological properties of DLC films in methanol. The relationship between the structure and properties of the films affected by bias voltage was systematically examined to enhance the service performance of the MoDLC coating in methanol. The results confirmed that Mo-doped DLC films exhibited considerable microstructural differences with variable bias, which further verified the performance of the film. The optimised bias voltage (600 V) resulted in the highest sp3 hybridisation bond content in the MoDLC coating, leading to the highest nano-hardness and H/E values. In addition, the 600 V treated MoDLC had a stable friction process and low wear rate (5.2 × 10−8 mm3/(N·m)) in methanol. The wear results showed that abrasive wear was dominant for MoDLC films in methanol, but oxidation wear and corrosion wear cannot be ignored for high-performance MoDLC films.