Preparation Of Magnetron Sputtered MoN-based Coatings And Research On Friction Wear Characteristics In Wide Temperature Range

At present,under the severe conditions of high temperature,high speed and heavy load etc.,various problems will occur in key components in modern aerospace and cutting tools industries,such as severe friction and wear,component failure and low service life.Therefore,it is of great theoretical and practical value to develop coatings with continuous lubrication from room temperature to high temperature.In this paper,based on the combination of the nitride ceramics hard basic phase and multi lubrication phase and in-situ self-lubricating phase on the coating surface,a series of coatings with low friction coefficient and low wear over a wide temperature range were prepared.Their microstructures,mechanical and frictional properties were studied.The relationship between the microstructure and tribological properties of the coating was developed.Furthermore,the evolution of coating composition,structure and performance from room temperature to 700°C was revealed,as well as adaptive friction reduction mechanism and failure mechanism.A series of MoN coatings were prepared by using DC magnetron sputtering technology under different N₂ flow rates.The microstructure,mechanical properties and wide temperature range friction and wear properties of the MoN coatings were studied with N₂ flow rates.The results show that the coating is mainly composed of a metallic Mo phase and a small amount of face-centered cubic Mo₂N phase under low nitrogen flow.As the N₂ flow increases,the coating forms a nanocomposite structure of MoN,Mo₂N,and Mo multiphase mixture.At the normal temperature,the friction coefficient of the MoN coating can reach a minim?m of about 0.35 and the wear rate is2.84×10^-7mm³N^-1m^-1.Due to the severe oxidative wear of the coating at high temperatures,the wear rate of the coating will increase by two magnitude.The existence form of the carbon lubricating phase in the MoCN coating and the change rule of amorphous carbon with temperature were studied.By changing the carbon target current to adjust the content of carbon in the coating,the specific process parameters of the deposited MoCN coating were established.The effects of carbon contents on the microstructure,mechanical and and frictional properties MoCN coatings were studied.The results show that due to the presence of sp³C-C hybrid carbon with diamond-like structure in amorphous carbon and the reaction-enhancing phase Mo C phase,the hardness and elastic modulus of MoCN coatings reach 28.89 GPa and439.22 GPa,respectively,and the modulus of elasticity decreases with increasing carbon content.Amorphous carbon and Mo O₃ lubricating phase play a synergistic lubricating effect at a medi?m temperature of 300°C.When the friction temperature rises above 500°C,oxidation will occur and the lubrication effect will be lost.In addition,the annealing treatment will transform the amorphous carbon to graphitization in the MoCN coating.The mechanical properties and tribological properties of the MoN coating will be improved to a certain extent after heat treatment at 400°C.Composite coatings were prepared by adding Ag and Cu targets.The effects of different element doping,single doping and co-doping on the microstructures,mechanical and frictional behaviors were studied.The chemical effects of Ag and Cu on the friction surface were analyzed at different temperatures.The results show that doping of soft metal Ag or Cu will greatly weaken the hardness and elastic modulus of the composite coating,leading to the reduce in the wear resistance.At a medi?m temperature of 300°C,diffusion and release of Ag and oxidation of Cu occur on the friction surface.When it is above 500°C,the friction coefficient of the composite coating is reduced by in-situ generation of tribochemical silver molybdate and copper molybdate lubricant phases in the wear zone.