Fabrication And Properties Of Wear-resistant Self-lubricating Coatings With Wide Temperature Range

30Cr Mn Si alloy structural steel is widely used due to its excellent mechanical properties,but its wear resistance in wide temperature range is poor,which limits its application in medium and high temperature environment.In this paper,a series of composite coatings were successfully prepared on the surface of 30Cr Mn Si alloy structural steel by laser cladding with Ni Cr alloy powder,Cr₃C₂,WS₂,Ca F₂and Ce F₃·La F₃composite powder as raw materials.The phase structure,microstructure,microhardness and friction and wear characteristics of the composite coating in a wide temperature range?from room temperature to 800??were researched by means of optical microscope,scanning electron microscope,energy dispersive spectrometer,X-ray diffractometer,hardness tester and friction and wear detection equipments.In addition,the wear mechanism of the composite coating with different components was elucidated by observing and analyzing the worn surface micro morphology of each coating.The results show that the content of Cr S and Ca S in Ni Cr/Cr₃C₂-WS₂-Ca F₂ composite coating increases with the increase of WS₂content in alloy powder.When the content of WS₂in the powder is 5wt%and 7.5wt%,WS₂in the two coatings can hardly be detected and the microstructure is very similar,which is mainly composed of reticulated?phase and irregular carbide.However,when the content of WS₂in the powder reaches10wt%,the grains in the coating are the smallest,and cluster like Fe W₂S₄-Cr₇C3 eutectic structure and needle like Ca S-Cr S eutectic structure appear in the microstructure.The average microhardness of the coating up to 804HV_0.2,which is 2.7 times that of the substrate.The wear loss rate of the coating at room temperature is only 1/10 of that of the substrate,and the wear mechanism at room temperature is adhesive wear with slight abrasive wear.The friction coefficient of the coating at 400?is 0.39,which is 37%lower than that of the substrate.The main wear mechanism is adhesive wear and slight fatigue wear.When the temperature reaches 800?,there are many peeling pits on the worn surface of the coating,mainly oxidation wear and fatigue wear.The laser cladding Ni Cr/Cr₃C₂-WS₂-Ce F₃·La F₃composite coating is mainly composed of grid like composite carbide,irregular elliptical?phase and Ni₁₇W₃eutectic structure.Furthermore,the grain size of the coating gradually decreases from the bottom to the top,and consists of plane crystal,cellular crystal or dendrite,equiaxed crystal in turn.When the content of WS₂and Ce F₃·La F₃in the powder is 7.5wt%,the microhardness of the coating is the highest,the average value is 790HV_0.2,which is 1.6 times higher than that of the matrix.The friction coefficient of the coating at room temperature is about 0.4,which is obviously lower than that of the substrate.The worn surface of the coating is clean and smooth,with only a small scratch.The wear mechanism is slight abrasive wear.The weight loss of the coating at 400?is only 0.8mg,which is about 1/9 of the base material.There are many transfer films on the worn surface of the coating.The main wear mechanism is adhesive wear with weak abrasive wear.The friction coefficient of the coating at 800?is 0.3,which is much lower than 0.82 of the substrate.There is oxide film on the worn surface,and the main wear mechanism is oxidation wear and adhesive wear.At the same time,the main element content of the wear area and the non wear zone of the coating has almost no change at 800?,which shows that the coating can maintain the original composition at high temperature,and the added rare earth metal fluoride can effectively reduce friction and wear at high temperature.