期刊
WEAR
卷 486, 期 -, 页码 -出版社
ELSEVIER SCIENCE SA
DOI: 10.1016/j.wear.2021.204107
关键词
Grease; Friction; Additive; Graphene oxide; Electrical contacts; 4-ball tests
资金
- SIO Grafen (Vinnova) [2015-01467]
The type of thickener has a significant impact on wear and tribofilm formation, with polypropylene thickener showing more wear in steel contacts. Graphite, graphene oxide, and reduced graphene oxide additives did not have a significant effect on friction and wear in the grease.
Two types of thickener systems, lithium complex (LiX) and polypropylene (PP), were chosen to evaluate graphite, graphene oxide (GO) and reduced graphene oxide (rGO) as grease additives at a concentration of 0.1 wt %. To enhance the additive dispersibility, a mixture of polyalphaolefin oil (PAO) and oil soluble synthetic polyalkylene glycol (OSP-68) was used as base oil. The greases were evaluated in i) silver-coated copper contacts simulating high-load electrical contact applications subjected to fretting and ii) a steel/steel 4-ball wear test equipment. The additives showed no positive effect on friction and wear, neither in fretting nor in 4-ball tests. However, there is a statistically significant difference in wear scar diameter on the 4-ball steel contacts between the two thickener types, LiX and PP. Thus, the PP-grease lubricated steel contacts showed more wear and more tribofilms of iron oxide and grease constituents, indicating more metal-to-metal contact. Hence, the thickener type has a larger impact on the lubricating performance of the grease than do the graphite, GO and rGO additions. The results demonstrate that the addition of graphene-based materials to improve greases is not straightforward. Rather, the grease/graphene-based additive system is complex and many parameters influence the friction and wear results. Hence, more work is needed to obtain a better understanding and possibly better lubricating effects from the graphene-based additives.
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