Study On Preparation Processes And Tribological Properties Of Solid Lubrication Coatings On 40Cr Surface

Gear,as an important component of mechanical transmission devices,and have been widely used and developed in many fields such as automation,automobiles,aerospace.Gears are usually used in special working conditions,such as high speed,heavy load and high temperature,which also puts forward higher requirements on gear performance.Tooth surface wear is one of the main failure modes of gears,and improving the friction-wear resistance of gear surfaces is one of the effective ways to improve gear transmission performance.Research shows that the friction-wear resistance of gear can be improved from two aspects:one is improve the surface hardness of the material,and the other is to introduce a lubricating medium.Mo is an important steel strengthening element and thermal-diffusion molybdenizing is one of the methods uesd for chemical surface modification of steel..Mo-based coatings have high hardness,high melting point and good wear resistance.Compared with traditional liquid lubricants,solid lubricants have better self-lubricating action and application prospect.In this paper,gear material 40Cr steel is used as the matrix,and Mo-containing layer and FeS solid lubricating film are prepared on the material surface.The main work are as follows:（1）Mo-coatings were prepared on 40Cr steel by pack-cementation treatment via induction-furnaceand box-furnace heating.Microstructure,element distributions,phases of various samples prepared by induction heating molybdenizing treatment at 1000～1300℃ were characterized by the field emission gun scanning electron microscope（FEG-SEM）and X-ray diffraction（XRD）.The evolution mechanism of the microstructure of molybdenizing by induction heating is described.The hardness and tribological properties of Mo-containing layer samples are tested.（2）Solid lubricating coating were prepared on 40Cr steel by double glow plasma sulfurizing treatment at 220～300℃.The effect of temperature on coating thickness,morphology and lubricating properties was studied.（3）The induction heating molybdenizing samples are combined with chemical sulfurizing treatment and double glow plasma sulfurizing treatment respectively.Explore the preparation process of soft-hard gradient coating to obtain Mo-containing layer and sulfide solid lubricating composite coating.Microstructure,element distributions and tribological properties of the coating were characterized and studied.By analyzing the experimental results,the following conclusions are obtained:（1）Induction-furnace is more effective than box-furnace.The results showed that a30～70μm thick Mo-containing layer was formed by induction heating at 1000～1300℃,and with the increase of the holding temperature,the thickness of the Mo-containing layer shows an overall upward trend.The coating structure of the treated samples was composed of Mo-coating,transition layer,and affected-layer.The Mo-coating was mainly composed of Fe-Mo solid solution and carbides phase,the transition layer consisted of alloy pearlite,and the affected layer was a carbon-poor zone.（2）Studies show that the hardness of the Mo-coating is much higher than that of matrix.The friction coefficient and mass loss of the treated samples are lower than the untreated sample.Friction properties was significantly improved after the formation of the Mo-coating on the 40Cr steel.（3）The results showed that a 1.76～33.16μm thick sulfide coating was successfully prepared by double glow plasma sulfurizing treatment at 220～300℃.And the coating is composed of FeS,Fe_1-xS,and FeS₂ nano-micron spherical particles.Higher ion sulfurizing temperature will increase the FeS₂ content,limiting the layered sulfide to exert its lubricating properties.（4）Mo-containing layer and sulfide solid lubricating coating with soft-hard gradient characteristics can successfully prepar on 40Cr steel by the composite induction heating molybdenizing process and sulfurizing process.（5）The friction coefficient and mass loss of the Mo-containing layer and sulfide solid lubricating composite coating sample are lower than the untreated sample.The surface of the composite coating sample has a certain lubricating effect,which improves the surface tribological properties of 40Cr steel.