Friction of metal-matrix self-lubricating composites: Relationships among lubricant content, lubricating film coverage, and friction coefficient

Abstract

Metal-matrix self-lubricating composites can exhibit excellent tribological properties owing to the release of solid lubricant from the matrix and the formation of a lubricating film on the tribosurface. The coverage of the lubricating film on a worn surface significantly influences the sliding process. However, it is difficult to quantify the film coverage owing to the thin and discontinuous character of the lubricating film and the high roughness of the worn surface. A quantitative characterization of the lubricating film coverage based on X-ray photoelectron spectroscopy (XPS) analysis was developed in this study. The friction tests of Cu-MoS 2 composites with a MoS 2 content of 0-40 vol% were conducted, and the worn surfaces of the composites were observed and analyzed. Further, the influence of the MoS 2 volume content on the coverage of the lubricating film on the worn surface was investigated. The relationships among the volume fraction of the lubricant, coverage of the lubricating film, and the friction coefficient were established. The friction model for the metal matrix self-lubricating composites was developed and verified to facilitate the composition design and friction coefficient prediction of self-lubricating composites.

Tribological behavior and microstructural evolution of lubricating film of silver matrix self-lubricating nanocomposite

“…The lubricating film containing rich solid lubricants can shear easily, which reduces the friction coefficient of the nanocomposite [3,23]. The transfer film on the worn counter disc surface has also been reported in other studies on metal matrix self-lubricating composites [7,13,23].…”

“…When the concentration of solid lubricants in metal matrix self-lubricating composites is greater than 5 wt%, the lubricating effect of the solid lubricants is more pronounced, as reported by Wu et al [17]. Xiao et al [7] synthesized Cu-MoS 2 composites by hot-press sintering, and their results indicated that the friction coefficient and wear rate of Cu-MoS 2 composites reduced by 81.6% and 96.0% when the MoS2 content was increased from 0 vol% to 40 vol%, respectively. More recently, lubricating films on worn surfaces have garnered significant attention [18][19][20].…”

“…Their researches indicated that the lubricating films were formed on worn surfaces of the composites during the friction and wear process, reducing the wear rates and friction coefficients. The addition of solid lubricant, such as MoS2 and NbSe2, promotes the formation of lubricating films, enhancing the wear resistance of the materials [6][7][8][9]. Moreover, the direct contact between the pin and disc is prevented by the lubricating film, and the adhesive wear of the materials was inhibited [20,31].…”

“…The lamellar structure is easy to slip between crystal lamellar sheets due to the anisotropy crystal of TMDs [3][4][5]. As the typical solid lubricants, the addition of TMDs enhances the tribological properties of metal matrix self-lubricating composites (MMSCs), including TiSe 2 , NbSe 2 , MoS 2 and WS 2 [6][7][8][9]. Recently, MMSCs with low friction are widely used as bushes for industrial applications and sliding electrical contact materials [10,11].…”

Nanolubricant additives: A review

“…Besides, lubricants which mainly include solid lubricants and liquid lubricants are widely used for lubrication. There are many advanced solid lubricants such as molybdenum disulfide (MoS 2 ) film [7], diamond-like coating [8], entangled carbon nanotube (CNT) film [9], and polymer material [10,11]. However, their tribological properties are directly influenced by the friction environment, and they are prone to being a wear-out failure after serving for a long time.…”