Preparation And Tribological Properties Of Ni-based Solid Lubricating Composite Coatings

The extreme friction environment conditions,such as vacuum,high speed,strong radiation,strong corrosion and high temperature,not only limits the use of liquid lubricants,but also has brought great challenges to the service life of high-precision instruments on the field of aerospace,such as satellites,aviation rockets.How to improve the lubrication effect between working parts,maintain the low friction coefficient and improve the service life of the aerospace instrument under the above extreme friction environment is the important of this study.The MoS₂,WS₂ solid lubricants were selected to replace the liquid lubricants.The co-deposition of MoS₂ or WS₂ with metal nickel was achieved by electrochemical deposition method,which makes up the drawback of the low hardness of single solid lubricant coating and the high friction coefficient of single metal nickel coating.This thesis studied the effects of different concentrations of MoS₂ and WS₂ on the morphology,phase and tribological properties of Ni-MoS₂ and Ni-WS₂ composite coatings to determine the optimum concentrations of MoS₂ and WS₂.The high temperature frictional properties of Ni-MoS₂ and Ni-WS₂ composite coatings at the optimum concentration were investigated,and the optimum temperature of composite coating was determined.Based on the above experimental data,the main conclusions are as following:1.The friction coefficient of Ni-WS₂ composite coating is better than that of Ni-MoS₂ composite coating at room temperature,but all the lubrication effect is better than that of pure nickel coating under the conditions of GCr 15,20 N load.The lowest friction coefficient at room temperature was obtained at a value around 0.02 0.03 or 0.01⁰.03 from the coating which was deposited in the electrolyte solution with a 30 g.L-1MoS₂ or WS₂ concentration.2.The operating temperature of Ni-WS₂ composite coating is higher than Ni-MoS₂ composite coating under high temperature friction conditions.The friction coefficient of the Ni-MoS₂ composite coating remained in the0.02 to 0.05 at below 300 ?,When the temperature went up to 400 ?,the friction coefficient manifested a continuous increase to 0.15,because the MoS₂ was gradually oxidized into MoO₃,and therefore lost its lubrication ability;The friction coefficient of the Ni-WS₂ composite coating remained in the 0.01 to 0.05 at below 400 ?,When the temperature went up to 400 ?,the friction coefficient manifested a continuous increase to 0.12,becausethe WS₂ was gradually oxidized into WO3,and therefore lost its lubrication ability.3.The reduction potential for Ni ions becomes increasingly negative with the increase in MoS₂ or WS₂ concentration.It is suggested that the MoS₂ or WS₂ particles have a certain hindrance to the nickel crystalin in the composite deposition system,promoting the cathode polarization and improving the crystallinity of the coating.