Design of an Ultra-Thick Film and Its Friction and Wear Performance under Different Working Conditions

Abstract

Tantalum (Ta)/Ti/TiN/Ti/diamond-like carbon (DLC) (referred to as TTTD film) and Ta/Ti/TiN/TiCuN/Ti/DLC (referred to as ultra-thick film) films were designed in this study, and the factors affecting the friction and wear properties of DLC films in sodium bicarbonate and lactic acid solutions were analyzed. Moreover, a thin film with a thickness exceeding 50 microns was prepared. Morphology and tribological and mechanical properties were analyzed by scanning electron microscopy, friction and wear testing machine, and nanoindentation instrument, respectively. The results show that the presence of a TiCuN interlayer increases the defects in the DLC film and the roughness of surface, reaching a roughness of 0.19 µm. Compared with the TTTD film, the TiCuN interlayer reduces the hardness and increases the residual stress, which is 0.52 Gpa and −6.08 GPa, respectively. The TTTD film has a smooth and dense surface structure and high hardness, causing it to more easily form boundary lubrication. However, the ultra-thick film has lower hardness and rough surface, which cannot effectively form boundary lubrication. Therefore, the friction coefficient of the ultra-thick film is higher than that of the TTTD film under different working conditions. In sodium bicarbonate solution, a double-hydrolysis reaction is more likely to occur, resulting in a higher friction coefficient than in lactic acid solution. The friction coefficient of the TTTD film has a longer running-in period, which is attributed to the oxides generated by the double-hydrolysis reaction and the precipitated sodium bicarbonate crystals. Finally, it was concluded that the surface quality and the internal bond structure of DLC film have a significant impact on the friction and wear properties. This provides a theoretical basis for the design of multilayer structures.