Study On Solid Self-lubricating Coatings By Laser Cladding

As the development of rail turnout and mining equipment,working conditions of spare parts are getting worse and worse.Failure rate of components is accelerated under the condition of no oil or less oil.Depositing a solid self-lubricating coating on substrate surface is one of the most effective ways to solve the above problems.The solid self-lubricating medium is added to the metal matrix as a lubricating component,which can form a lubricating film in the friction process,and show good antifriction performance.The coating prepared by laser cladding has good wettability,strong bonding force,uniformity,compactness,cleanliness and pollution-free,which can improve the surface friction of substrate.The wear resistance is improved obviously,thus the overall performance and service life of the material are also improved.In this paper,graphite/Ni,WS2/Ni and WS2+C/Ni Self-lubricating coatings were prepared by laser cladding technology.Ni50 was used as transition layer to form double-layer cladding coatings.The effects of type and contents of self-lubricating phase on structure and properties of the coatings were discussed.The phase composition and microstructure of the cladding layer were observed by X-ray diffractometer and high resolution scanning electron microscopy.The composition and distribution of the micro-area were analyzed by EDS.The microhardness was measured by microhardness tester,and the friction properties were studied by multi-functional friction and wear tester.The results are as follows:(1)The cladding layer has a good metallurgical bonding with matrix.In the fusion zone,there will be an obvious plane crystal band,the directional solidification tendency of dendrites in transition layer is remarkable,and interdendritic γ-(Ni,Fe)and M23C6 grow in eutectic mode.The formability of the coating is consecutive and beautiful,no pore and inclusion.(2)The main phases of graphite self-lubricating coatings are friction-reducing phase C,strengthening phase M23C6 and matrix phase γ-(Ni,Fe),graphite is uniformly distributed in the coatings,and the amount of unmelted graphite is more.With the increase of graphite friction-reducing phase,the hardness of self-lubricating coatings does not increase significantly.The maximum hardness value of coatings is 739.12HV0.05.Friction coefficient of coatings is contrary to the content of self-lubricating phase and the minimum friction coefficient of self-lubricating coatings with 20%content is 0.39.Also friction coefficient decreases gradually with the increase of load,and the minimum friction coefficient is 0.38 under 100N load.The main wear mechanisms of graphite self-lubricating coatings are adhesion wear and oxidation wear.(3)The main phases of WS2 self-lubricating coatings are friction-reducing phase CrS,Cr3S4,matrix phase y-(Ni,Fe)and strengthening phase M23C6.With the increase of WS2,the hardness of self-lubricating coatings increases obviously,and the maximum hardness of coatings is 1154.54HV0.05.Friction coefficient of coatings is inversely proportional to the content of self-lubricating phase,and the minimum friction coefficient is 0.40 with 20%WS2.Friction coefficient decreases gradually with the increase of load,the minimum friction coefficient is 0.41 under 100N load.The main wear mechanism of WS2 self-lubricating coating is abrasion.(4)The main phases of WS2-C self-lubricating coatings are friction-reducing phase CrS,Cr3S4,matrix phase y-(Ni,Fe),strengthening phase M23C6 and unmelted graphite.The maximum hardness of the coating is 1144.83HV0.05.Friction coefficient of coatings decreases gradually with the increase of load,and the friction coefficient of WS2-C self-lubricating coatings is 0.43 at 100N load;the hardness of WS2-C self-lubricating coatings is above 1144.83 HV0.05 and the maximum value is 1150 HV0.05.The main wear mechanisms is slight abrasive wear.