Investigation Of Microstructure And Properties Of Plasma Sprayed NiCrBSiNb Coating Remelted By Induction Process

Preparing coating on the surface of workpiece by thermal spraying technology can delay the failure of workpiece.However,based on the principle of coating deposition,there are inevitably defects such as pores and microcracks in the sprayed coating,and the bonding between the sprayed coating and the substrate is relatively poor.These characteristics of sprayed coating limit the application of thermal spraying technology to a large extent.Especially under some harsh service conditions,such as cyclic load,impact and corrosion environment,only by means of thermal spraying to modify the surface of the workpiece,it is still difficult for the workpiece to meet the service requirements,therefore,it is necessary to explore an effective process to further treat the sprayed coating,and make up for defects of the microstructure and performance of sprayed coating,thus the potential of the coating can be fully exploited and the service life of the workpiece can be greatly extended.Remelting treatment can effectively reduce or even eliminate the microdefects of the sprayed coating,improve the interface bonding between the sprayed coating and the substrate,thus improve the properties of the sprayed coating.Therefore,in this paper,NiCrBSiNb sprayed coating was prepared on the surface of the quenched and tempered AISI 1045 steel ring by plasma spraying method,and induction remelting was carried out for the sprayed coating to fabricate the remelted coating.On this basis,the effect of induction remelting on the microstructure and properties of the coating was studied.Results showed that,after induction remelting,the microstructure of the coating was improved,the porosity and cracks were almost eliminated,and the density of the coating was greatly improved;the interface bonding between the coating and the substrate changed from mechanical bonding to metallurgical bonding.In addition to Fe₃C,Ni₃Si,Cr₂₃C₆ strengthening phases,Nb C in situ precipitated in the coating and had a good coherent relationship with the substrate;After induction remelting,the mechanical properties of the coating were improved,the micro Vickers hardness increased from 780 HV_0.1 to 1350 HV_0.1,with an increase of 73.1%;the elastic modulus increased from 158 GPa to 236 GPa,with an increase of 49.4%;and the fracture toughness increased from 1.23 MPa·m^1/2 to 28.2 MPa·m^1/2.In addition,in this paper,the effect of induction remelting on the tribological properties of the coating were respectively studied by friction and wear test and rolling contact fatigue test,results revealed that,remelting treatment can improve the wear performance of the coating,and the wear damage of remelted coating was lighter than that of sprayed coating under same wear conditions;moreover,after induction remelting,the contact fatigue performance of the coating was also improved,the fatigue life of the coating was greatly extended and the fatigue failure modes of the coating changed from interface delamination to pitting and spalling.Finally,the effects of induction remelting on the corrosion resistance of the NiCrBSiNb coating were studied by corrosion immersion test and electrochemical corrosion test,the results showed that,the corrosion damage of remelted coating was lighter than that of sprayed coating when immersed in 1 mol/L H₂SO₄ solution and 1 mol/L HCl solution;besides,the results of electrochemical corrosion test showed that the corrosion potential of remelted coating was higher than that of sprayed coating,while the corrosion current density was lower than that of sprayed coating,the electrochemical impedance fitting results showed that the resistance of remelted coating was significantly higher than that of sprayed coating.In general,the corrosion resistance of induction remelted coating was better than that of plasma sprayed coating.