Tribological Properties Of Graphite-MoS₂ Coating And Its Application In Deep Groove Ball Bearing

The long service life and harsh working environment of aeronautical and space vehicles cause severe frictional wear and even failure of the bearings working in aeronautical and space environment.Therefore,it is urgent to seek a lubricant with antifriction and wear resistance to reduce the friction and wear of aeronautical and space bearings.Molybdenum disulfide?MoS₂?is a common solid lubricant for bearings.Although it is widely used in aeronautical and space industry,the lubricating effect of MoS₂ is limited and it is easily oxidized at high temperatures.Thus,its tribological properties should be further improved to meet the increasingly stringent antifriction and wear resistance requirements.In this paper,the MoS₂ composite coating is prepared by doping graphite to MoS₂ to enhance the tribological properties of the pure MoS₂ coating,and further this composite coating is applied to the deep groove ball bearing used widely in aeronautical and space.The tribological and mechanical properties of the graphite-MoS₂ coating are explored using a combination of frictional experiment and numerical simulation.The present study is sponsored by the Fund Project of the National Natural Science Foundation of China?No.51775067?,which is named after"multi-body lubrication and thermal characteristics of high-speed rolling bearing includding the influence of rotor dynamic performance",and the National Key Laboratory of Mechanical Transmission of Chongqing University?No.106112016CDJZR288805?,which is named as“failure mechanism and regulation method of interface bearing performance of aerospace bearing components”.The graphite-MoS₂ composite coating is selected as the research object,whose tribological properties and friction and wear mechanism at room and high temperatures are studied experimentally.Meanwhile,the finite element analysis of contact performances for the deep groove ball bearing lubricated with the composite coating is made to provide theorectical for the design and application of solid lubricant coatings for the aeronautical and space bearings.The main research contents and results of the present paper are as follows:Firstly,the friction and wear behavior of the graphite-MoS₂ composite coating at room temperature are investigated under the varied graphite content,applied load and rotational speed.The experiment results indicate that adding graphite can effectively reduce the friction coefficient of MoS₂ coating and improve its wear resistance.The graphite-MoS₂ coating exhibits the best tribological performance at the graphite content of 20 wt.%.The composite coating exhibits the best friction reduction and wear resistance behaviors at the applied load of 10 N and rotational speed of 500 rpm.Simultaneously,the composite coating is worn through at the critical applied load of 20N.Further,effects of graphite content,test temperature,applied load and rotational speed on the tribological properties of the graphite-MoS₂ composite coating at high temperatures are studied experimentally.The experiment results indicate that the graphite content of 20-33 wt.%?temperature are 100?200 and 300??can effectively improve the antifriction and wear resistance properties of the MoS₂ coating,and the optimal graphite content is 20 wt.%.The transition temperature of the graphite-MoS₂composite coating?graphite content is 20 wt.%?is 200°C.The coating shows the best tribological performance at 200°C.When the temperature is continuously increased to500°C,the oxidative failure of the composite coating occurs.The composite coating exhibits the best friction reduction and wear resistance at the applied load of 10 N and the rotational speed of 500 rpm?temperature is 200??.Then,based on the above friction and wear experiment results of graphite-MoS₂coating under room and high temperatures,the multiple linear regression analysis method and least squares principle are used to obtain the friction coefficient prediction model of the graphite-MoS₂ coating under the varied graphite content,applied load,rotational speed,and test temperature used in the experiment.The validity of the prediction model is verified with the reserved test results.Finally,using the same working conditions and friction coefficients of the prediction model,the contact mechanical properties of the graphite-MoS₂ coated deep groove ball bearing are investigated through the finite element method.The numerical results show that the graphite-MoS₂ coating can effectively improve its contact mechanical properties,thereby prolonging its service life.Decreasing the applied load and rotational speed can reduce the possibility of failure for the coating caused by the excessive stress or temperature rise.At 200°C,the graphite-MoS₂ coated deep groove ball bearing exhibits the lowest heat generation and best contact mechanical properties.