Self-Lubricating Properties of Carbon-Filled Oblique Angle Deposition Porous TiN Coating

To address the issue of easy removal of the lubricant phase by frictional behaviors, this study provided an innovative approach to fabricate porous TiN-based coatings subsequently filled by lubricant carbon. The process commenced with oblique angle deposition of porous TiN coatings to form a reservoir for storing lubricants. Subsequently, carbon was filled into the pores through sequential hydrothermal carbonization and thermal treatment. Mechanical and structural characterizations of porous TiN coatings reveal that as the working pressure increases from 0.27 to 0.8 Pa, the coating hardness increases from 12.64 to 20.36 GPa. Conversely, while the average pore size decreases, the overall porosity increases from 7.5% to 13.7%. As a result, the carbon-filled porous TiN coating deposited at 0.8 Pa exhibits superior tribological performance, maintaining a friction coefficient below 0.4 for 8100 s, which exceeds the ∼3000 s of coating deposited at a pressure of 0.27 Pa. Undoubtedly, this performance is also markedly better than that of nonoblique angle deposited TiN-C coatings, which display a friction coefficient of ∼0.85 at 1200 s. This coating also exhibits excellent wear resistance with a very low wear rate of 6.9 × 10–7 mm3/N·m. The wear mechanism is attributed to the continuous release of carbon from the pore TiN reservoirs to the wear track interface, which ensures the formation of a lubricating carbon film at the sliding contact interface, maintaining its effectiveness throughout the sliding process.