Test of Diamond-Like Coatings with Monocrystalline Carbon for Tribological Purposes

• Published in: Journal of friction and wear 2021-12, Vol.42 (6), p.478-483
• Main Authors: Levchenko, V. A., Buyanovskii, I. A., Samusenko, V. D.
• Format: Article
• Language: English
• Subjects: Argon ions; Carbon; Classical and Continuum Physics; Coatings; Coefficient of friction; Diamond films; Diamond-like carbon; Diamonds; Friction; Lubrication; Oleic acid; Phase diagrams; Physics; Physics and Astronomy; Room temperature; Ternary systems; Tribology
• ISSN: 1068-3666; 1934-9386
• DOI: 10.3103/S1068366621060040

The region of the possible existence of monocrystalline carbon is established on the sp 1 sp 2 sp 3 ternary phase diagram. This region has a homeotropically aligned two-dimensionally ordered structure of the sp 1 sp 3 hybridization type. The use of monocrystalline carbon as a coating on working surfaces of heavily loaded friction units allows covering these surfaces with a highly ordered homeotropically aligned layer of lubricating medium molecules. Monocrystalline carbon coatings-orientants with a thickness of 0.1 μm or higher were obtained by the pulsed condensation of carbon plasma in combination with additional irradiation with Ar + ions. As shown by the XPS method, monocrystalline carbon contains not only the sp 1 phase but also the sp 3 phase. According to tribological tests, the respective friction coefficients at room temperature for a steel–steel friction pair with friction in an inactive Vaseline oil, steel coated with amorphous carbon, and steel coated with monocrystalline carbon were 0.18, 0.21, and 0.1. In the same conditions, the coefficient of friction in the lubricating medium of the same oil but with an oleic acid additive of 1 wt % was 0.12. At higher temperatures, the difference between the coefficients of friction for these tribocouplings was even more striking in favor of the monocrystalline coating. The analysis of the entire set of results allowed localizing monocrystalline carbon on a ternary phase diagram for assessing the possible regions of existence of diamond-like phases. The possibility of using the sp 3 / sp 1 hybridized states ratio as a criterion for choosing the optimal mode of synthesizing monocrystalline coatings-orientants is shown.