Study On Microstructure And Properties Of Tungsten Inert Gas Arc Remelted NiCr-Cr₃C₂ Coating By Plasma Spraying

NiCr-Cr₃C₂coating is a coating with excellent properties of high temperature resistance and wear resistance.Its common preparation method is plasma spraying,but the coating prepared by this method has many defects and poor interface bonding strength.The coating is prone to failure and the excellent properties it has cannot be fully utilizedIn this paper,the microstructure,mechanical properties,wear resistance and contact fatigue properties of NiCr-Cr₃C₂coating were studied.The NiCr-Cr₃C₂coating and the remelting coating were prepared successively on the 45 steel substrate by plasma spraying and TIG remelting.Scanning electron microscope(SEM),transmission electron microscope(TEM),energy spectrum analyzer(EDS),and X-ray diffraction(XRD)were used to analyze the microstructure and composition of the coating.The porosity was also characterized.The microhardness of the coating was measured by microhardness tester,and the elastic modulus and fracture toughness of the coating were characterized and calculated by nano indentation tester.The point-line friction and wear testing machine was used to test the wear resistance of the coating at room temperature,and the pin-plate wear testing machine was used to test the wear resistance of the coating at high temperature.The fatigue life of coating with different slip rate was tested by rolling and sliding fatigue testing machine.The microstructure and properties of the sprayed and remelted layers were compared.TIG remelting made the bonding mode between coating and substrate change from mechanical bonding to metallurgical bonding.The internal porosity of the coating decreased,and the defects such as cracks and unmelted particles decreased obviously.The phase of the remelted coating was different from that of the sprayed coating,the crystal structure was changed,and the internal structure was more uniform and dense.The main chromium carbides in the sprayed coating were Cr₃C₂and Cr₇C₃,and their lattice structures were both orthogonal structures.The chromium carbides in the remelted coating were Cr₃C₂,Cr₇C₃and Cr₂₃C₆,of which Cr₂₃C₆was cubic.TIG remelting treatment improves the mechanical properties of the coating.The surface hardness of the coating increased from 1007 HV_0.1to 1141 HV_0.1.The elastic modulus increased from 187 GPa to 190 GPa,and the fracture toughness increased from1.55GPa·m^1/2to 6.53 GPa·m^1/2,with a significant increase of 321.3%.The wear volume of the remelted coating is significantly smaller than that of the sprayed coating in the ball-disk wear test at room temperature.In the pin-disk wear test,the friction coefficients of the sprayed coating and the remelted coating at different temperatures were not much different,whiled the weight loss of the remelted coating was always less than that of the sprayed coating,and the reduction range is about 75%.TIG remelting treatment significantly improves the wear resistance of the coating.In the contact fatigue test.The sprayed coating is prone to delamination failure,and its contact fatigue life data cannot be recorded.The failure modes of remelted coating were mainly wear failure and peeling failure.The metallurgical combination between the remelted coating and the substrate avoided the occurrence of delamination failure.The uniform density of remelted coating reduced the probability of wear failure.So,TIG remelting treatment improves the contact fatigue resistance of the coating.