Preparation And Tribological Properties Of Graphene/transition Metal Sulfide Nanocomposites

Transition metal chalcogenides(MS2,M=Fe, Mo, W, etc) have been widely used as lubricant oil additives or solid lubricant in the field of tribology due to its novel structure and outstanding physical and chemical properties. The unique two-dimensional crystal structure of graphene has better performance than the traditional carbon materials. Graphene/transition metal sulfide composites can not only exert the excellent properties of graphene, such as high specific strength and specific modulus, but also can further improve the tribological properties of transition metal sulfides. In this paper, the graphene/transition metal sulfide nanocomposites were prepared by a facile and effective hydrothermal method. The morphology, microstructure and tribological properties of the nanocomposites were studied systematically. The friction and wear mechanism of graphene/transition metal sulfide nanocomposites was put forward on the basis of experiment. The main contents are as follows:(1) The reduced graphene oxide/FeS2(RGO/FeS2) nanocomposites were synthesized by hydrothermal method, and FeS2 particles were well distributed on RGO nanosheets. With the increase of the concentration of GO, the average particle size of the FeS2 particles not only gradually decreased from 2000 nm to 200 nm but also the corresponding morphologies were changed from polygon to sphere-like. Furthermore, the performance of the RGO/FeS2 nanocomposites as lubricating oil additives was investigated on a ball-plate tribotester. The results indicated that RGO/FeS2 could improve the load-carrying capacity dramatically, as well as the friction-reduction and anti-wear properties of the paraffin oil. In addition, higher GO content(0-0.20 g) is beneficial to improve the lubrication properties of RGO/FeS2 nanocomposites.(2) The reduced graphene oxide/MoS2(RGO/MoS2) nanocomposites were synthesized through hydrothermal method. MoS2 nanospheres composed of many petal-like nanosheets were well attached to the creased RGO sheets. The diameter of MoS2 nanospheres is about 150 nm. In addition, the tribological properties of the nanocomposites as a solid lubricant of Fe matrix self-lubricating material were investigated. Fe matrix self-lubricating material was prepared by powder metallurgy method. The raw material included Fe powder, Ni WCr alloy powder and Cu powder. Results showed that Fe matrix materials with suitable RGO/MoS2 content exhibited excellent wear-friction properties over a wide temperature range, and the RGO in RGO/MoS2 nanocomposites played an important role in the hardness and tribological performance of composites. While MoS2 was decomposed during the sintering process, forming the eutectic sulfides of chromium(CrxSx+1) with the metal Cr in the matrix. CrxSx+1 has the effect of lubrication at high temperature.(3) Interfacial combination between fillers and matrix is an important factor to affect the comprehensive performance of composites. The effects of electroless nickel plating on the composition, microstructure and tribological properties of RGO/MoS2 nanocomposites were studied systematically. Results showed that a thick layer of nickel was deposited on the surface of RGO/MoS2 nanocomposites, and the gap between the slice and slice of MoS2 particles disappeared, forming a more complete sphere. In addition, the wettability and interfacial bonding between RGO/MoS2 and Fe matrix were obviously improved by nickel plating. Fe matrix materials with nickel coated RGO/MoS2 have higher density, hardness and better tribological properties than Fe matrix materials with uncoated RGO/MoS2.