Self-lubricating properties of carbon filled oblique angle deposition porous TiN coating

To address the issue of easy removal of lubricant phase by frictional behaviors, this study provided an innovative approach to fabricate porous TiN-based coatings subsequently filled by lubricants carbon. The process commenced with oblique angle deposition of porous TiN coatings, creating reservoir to store the carbon lubricants. The mechanical performance, pore size, and porosity can be adjusted through changing deposition gas pressure. The hardness increases from 12.64 to 20.36 GPa, and the pore size decreases, but the porosity increases from 7.5–13.7% with rising working pressure from 0.27 to 0.8 Pa. Then, the carbon was filled into the pore of porous TiN through sequential hydrothermal carbonization and thermal treatment. The friction test results show that the carbon filled porous TiN coating deposited at 0.8 Pa possesses the excellent tribological performance, maintaining the friction coefficient below 0.4 for 8,100 s, which exceeds the ~ 3,000 s of coating deposited at sputtering pressure of 0.27 Pa. There is no doubt that tribological performance of carbon filled porous TiN coatings are better than non-oblique angle deposited TiN-C coatings (µ ≈ 0.85 at 1,200 s). This coating also exhibits excellent wear resistance with a very low wear rate of 6.9 × 10 ^− 7 mm ³ /N⋅m. The wear mechanism originated from continuous carbon release from pore TiN reservoirs to the wear interface, maintaining lubricating carbon films during sliding contact.