Understanding the interfacial behaviors during superlubricity process of a-C:H film coated on the rough bearing steel surface. (July 2022)

• Record Type: Journal Article
• Authors: Wang, Yinhui; Deng, Wenli; Qi, Wei; Chen, Xinchun; Xu, Jianxun; Zhang, Chenhui
• Is Part Of: Tribology international. Volume 171(2022)
• Publication Date: 2022-07
• Subjects: A-C:H film -- Surface asperity -- Superlubricity -- Hydrogen content -- Real contact area; Tribology -- Periodicals; 621.89
• DOI: 10.1016/j.triboint.2022.107558
• Languages: English
• ISSNs: 0301-679X

Abstract

Abstract: Hydrogenated amorphous carbon (a-C:H) film can achieve superlubricity in inert gas atmosphere in the previous reports, but the roughness (at atomic scale or several nanometers range) of most employed substrate surfaces for coating is much smaller than the grade of engineering application. Aiming at disclosing the influence mechanism of asperities of rough surface with a-C:H film on superlubriciy, in this work, the a-C:H film was deposited on the rough bearing steel surface (arithmetic mean height Sa ~ 128 nm) by ion beam deposition method. The tribological tests show that the friction coefficient can maintain a superlow level in the range of 0.004 ~ 0.008 for at least 80, 000 sliding cycles. Multiwavelength Raman spectra indicate that more rubbing cycles lead to the consumption of the hydrogen atoms and the increasing of the sp 2 clustering of a-C:H film coated on counterpart balls. The hydrogen content after the maximum cycles rubbing is reduced by 3.95–7.85% in contrast to the fewer friction cycles. The estimated contact pressure of the rough surface rises more than 4 times as compared with the apparent contact pressure of 1.17 GPa for the smooth surface. The results highlight that although the hydrogen atoms in summits of surface are consumed during friction, the materials keeping the original hydrogen content of a-C:H film in the valley gradually participate in rubbing and undertake the role of superlubricity. These findings can provide a guidance towards a possibility of the application of highly-hydrogenated a-C:H film coated on the moving parts of industry equipment. Graphical Abstract: Interfacial evolution of self-mated a-C:H film coated on rough surface during superlubricity sliding ga1 Highlights: Superlubricity is achieved on rough steel surface (Sa ~ 128 nm) coated with a-C:H film. The real load capacity of the film-coated asperity is confirmed to be much stronger than the nominal one. The interfacial behaviors depending on the friction-induced loss of hydrogen is revealed.