Tribological properties of amorphous hydrogenated (a-C:H) and hydrogen-free tetrahedral (ta-C) diamond-like carbon coatings under jatropha biodegradable lubricating oil at different temperatures

• Published in: Applied surface science 2014-10, Vol.317, p.581-592
• Main Authors: Mobarak, H.M., Masjuki, H.H., Mohamad, E. Niza, Kalam, M.A., Rashedul, H.K., Rashed, M.M., Habibullah, M.
• Format: Article
• Language: English
• Subjects: Coating; Coatings; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Diamond-like carbon (DLC) coatings; Diamond-like carbon films; Exact sciences and technology; Friction; Graphitization; Jatropha; Lubrication; Physics; Stainless steels; Tantalum; Wear; Wear rate
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/j.apsusc.2014.08.168

•We tested a-C:H and ta-C DLC coatings as a function of temperature.•Jatropha oil contains large amounts of polar components that enhanced the lubricity of coatings.•CoF decreases with increasing temperature for both contacts.•Wear rate increases with increasing temperature in a-C:H and decreases in ta-C DLC.•At high temperature, ta-C coatings confer more protection than a-C:H coatings. The application of diamond-like carbon (DLC) coatings on automotive components is emerging as a favorable strategy to address the recent challenges in the industry. DLC coatings can effectively lower the coefficient of friction (CoF) and wear rate of engine components, thereby improving their fuel efficiency and durability. The lubrication of ferrous materials can be enhanced by a large amount of unsaturated and polar components of oils. Therefore, the interaction between nonferrous coatings (e.g., DLC) and vegetable oil should be investigated. A ball-on-plate tribotester was used to run the experiments. Stainless steel plates coated with amorphous hydrogenated (a-C:H) DLC and hydrogen-free tetrahedral (ta-C) DLC that slide against 440C stainless steel ball were used to create a ball-on-plate tribotester. The wear track was investigated through scanning electron microscopy. Energy dispersive and X-ray photoelectron spectroscopies were used to analyze the tribofilm inside the wear track. Raman analysis was performed to investigate the structural changes in the coatings. At high temperatures, the CoF in both coatings decreased. The wear rate, however, increased in the a-C:H but decreased in the ta-C DLC-coated plates. The CoF and the wear rate (coated layer and counter surface) were primarily influenced by the graphitization of the coating. Tribochemical films, such as polyphosphate glass, were formed in ta-C and acted as protective layers. Therefore, the wear rate of the ta-C DLC was lower than that of the-C:H DLC.