Improvement of the lubrication properties of grease with Mn 3 O 4 /graphene (Mn 3 O 4 #G) nanocomposite additive
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ISSN 2223-7690 CN 10-1237/TH
RESEARCH ARTICLE
Improvement of the lubrication properties of grease with Mn3O4/graphene (Mn3O4#G) nanocomposite additive Bao JIN1, Guangyan CHEN1，Jun ZHAO2,*, Yongyong HE1,*, Yiyao HUANG2, Jianbin LUO1 1
State Key Laboratory of Tribology, Tsinghua University, Beijing 100084, China
2
College of Mechanical and Electrical Engineering, Beijing University of Chemical Technology, Beijing 100029, China
Received: 09 March 2020 / Revised: 29 April 2020 / Accepted: 30 May 2020
© The author(s) 2020. Abstract: Although grease can effectively lubricate machines, lubrication failure may occur under high speed and heavy load conditions. In this study, Mn3O4/graphene nanocomposites (Mn3O4#G) were synthetized using a hydrothermal method as lubricant additives. The lubrication properties of compound grease with Mn3O4#G nanocomposite additive under heavy contact loads of 600–900 N (3.95–4.59 GPa) were investigated. First, the nanocomposites were dispersed into L-XBCEA 0 lithium grease via successive electromagnetic stirring, ultrasound vibration, and three-roll milling. Compound grease with additives of commercial graphene (Com#G) was also investigated for comparison. Tribological test results revealed that the trace amounts of Mn3O4#G (as low as 0.02 wt%) could reduce the coefficient of friction (COF) of grease significantly. When the concentration of Mn3O4#G was 0.1 wt%, the COF and wear depth were 43.5% and 86.1%, lower than those of pure graphene, respectively. In addition, under the effect of friction, the microstructure of graphene in Mn3O4#G nanocomposites tends to be ordered and normalized. Furthermore, most of the Mn3O4 transformed into Mn2O3 owing to the high temperature generated from friction. Using the Ar gas cluster ion beam sputtering method, the thickness of the tribofilm was estimated to be 25–34 nm. Finally, the improvement of the lubrication properties was attributed to the synergistic effect of the adsorbed tribofilm, i.e., the graphene island effect and the filling effect of Mn3O4#G. Keywords: friction; nanocomposite additive; graphene; synergistic lubrication
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Introduction
Lubricants are widely used for reducing equipment friction and wear, thereby increasing the service life of machines, especially in heavy contact load conditions [1, 2]. More than 30% of the energy consumption of machines is related to mechanical friction and most of the mechanical failures result from wear [3, 4]. Therefore, it is crucial to improve the anti-friction and wear reduction properties of lubricants under heavy contact load [5, 6]. Ouyang et al. [7] investigated the tribological properties of three dimensional (3D) hierarchical porous graphene
as an additive in grease with three motion modes under heavy load conditions (2.55 GPa). Nehme [8] studied the tribological properties of zinc dialkyl dithiophosphates (ZDDP) with added submicron particles of titanium fluoride or iron fluoride along with polytetrafluoroethylene under heavy load condition (336 N; 2.6 GPa) and different speeds. He also
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