Investigation on MoS_2 and Graphite Coatings and Their Effects on the Tribological Properties of the Radial Spherical Plain Bearings

With constant enlargement of the application areas of the spherical plain bearings,higher quality lubrication of the bearings is required.To solve the lubricating problems of spherical plain bearings under high temperature,high vacuum,high speed,heavy loads and strong oxidation conditions,it is urgent for us to develop more excellent self-lubricating technologies.In this paper,the bonded solid lubricant coatings,which use inorganic phosphate as the binder,the mixture of MoS2 and graphite with two different weight proportions as the solid lubricant,are prepared by spraying under three different spray gun pressures.The bonding strength tests on the coatings show that the best spraying pressure is 0.2 MPa and the better mixing proportion of MoS2 to Graphite is 3：1.Then for the radial spherical plain bearings with steel/steel friction pair,after the coatings are made on the inner ring outer surfaces,the friction coefficient,the wear loss and the friction temperature of the bearings under four oscillating frequencies are investigated by a self-made tribo-tester.The test results,SEM of the worn morphologies and EDS of worn areas show that tribological properties of the bearing are obviously improved by the bonded solid lubricant coatings.When sprayed under the spray gun pressure of 0.2 MPa,the bearings have better anti-friction and anti-wear properties than those sprayed under 0.1 MPa and 0.3 MPa.Further as proved from the XPS analysis,between the coating with 3：1 mixing ratio of MoS2 to Graphite and the coating with 1：1 ratio,the former has less oxidation occurred on the surface and therefore has better tribological characteristics than the latter.This paper provides a reference to developing a new product of the radial spherical plain bearings with high bonding strength,oxidation resistance and abrasion resistance.

Protective Graphite Coating for Two-Dimensional Carbon/Carbon Composites

Two-dimensional carbon/carbon(2D C/C)composites are a special class of carbon/carbon composites,generally obtained by combining resin-impregnated carbon fiber clothes,which are then cured and carbonized.This study deals with the preparation of a protective coating for these materials.This coating,based on graphite,was prepared by the slurry method.The effect of graphite and phenolic resin powders with different weight ratios was examined.The results have shown that the coating slurry can fill the pores and cracks of the composite surface,thereby densifying the surface layer of the material.With the increase of the graphite powder/phenolic resin weight ratio,the coating density is enhanced while the coating surface flatness decreases;moreover,the protective ability of coating against erosion first increases(from 1:3 to 2:2)and then decreases(from 2:2 to 3:1).When the weight ratio is about 1:1,the coating for 2D C/C composites exhibits the best erosion resistance,which greatly aids these materials during gas quenching.In this case,the erosion rate is decreased by approximately 41.5%at the impact angle of 30°and 52.3%at normal impact,respectively.This can be attributed to the ability of the coating slurry to infiltrate into the substrate,thereby bonding the fibers together and increasing the compactness of the 2D C/C composites.

High Temperature Decomposition Behavior of CaZrO3 Coating on Graphite for TiNi Alloy Melting

In order to restrain the carbon pollution, the feasibility of CaZrO3 coating was studied. The precursor powder was synthesized via solid-state reaction using metal calcium as a raw material. The protective coating on graphite was prepared by impregnation sintering method, and the effects of slurry viscosity, graphite density and coating thickness for coating were compared. The phase composition and microstructure of coatings were characterized, and the thermodynamic process was analyzed when the coating composition changed from CaZrO3 to ZrC. The results show that vacuum sintering can result in the decomposition of CaZrO3 and an intact ZrC coating with beautiful porous structure can be obtained.