Study On Microstructure,Properties And Residual Stress Of Ni-based Alloy Coating By Electromagnetic-Assisted Laser Cladding

For the high hardness nickel base alloy,due to the extremely cold and hot characteristics of laser cladding,the temperature distribution in the nickel base alloy coating was uneven,the residual stress was large,and the cladding layer was easy to crack,which affect the service life of the sample.Therefore,how to improve the stress and reduce the cracking sensitivity of the cladding layer was of great significance for improving the quality of the laser cladding coating.In this paper,in the process of laser cladding on the surface of industrial pure iron substrate,the steady-state magnetic field and alternating current were applied synchronously,the influence of electromagnetic field on the microstructure of cladding layer was studied by optical microscope(OM),scanning electron microscope(SEM),energy dispersive spectrometer(EDS)and X-ray diffraction(XRD);The performance of the cladding layer was studied by using Vickers micro-hardness tester,electrochemical corrosion,friction and wear;The X-ray diffraction method was used to measure the residual stress;Meanwhile,the cracking of the cladding layer was detected by penetrant inspection.The results were as follows:(1)The elongated precipitates in the cladding layer were broken,the structure was refined,and the number of pores was reduced;the number of hard phase Cr B was increased,the structure was evenly distributed.But when the electromagnetic parameter was 0.2 T+1600 A,Joule heating had a greater effect and the structure became coarse;the external electromagnetic field would not change the phase composition of the cladding layer,mainly including?-Ni,Cr B,Cr₇C₃ and Ni₃B.(2)As the electromagnetic parameters increased,the microhardness of the cladding layer first increased and then decreased.When the electromagnetic parameter was 0.2 T+1200 A,the average micro-hardness was up to 885.9 HV_0.2;After the electromagnetic field was applied to the laser cladding,the self-corrosion potential first increased and then decreased,and the self-corrosion current density first decreased and then increased.The corrosion resistance of the cladding layer was the best at 0.2T+1200 A;When electromagnetic field assisted laser cladding was not applied,the wear and friction coefficient of the coating were the highest,and the wear resistance was poor.After electromagnetic field assisted laser cladding was applied,the wear amount and friction coefficient of the coating decreased first and then increased,reaching the lowest at 0.2 T+1200 A,and the wear resistance of the coating was improved.(3)The surface and junction of the cladding layer were tensile residual stress,and the heat-affected zone was residual compressive stress.With the gradual increase of electromagnetic parameters,the residual stress in the cladding layer first decreased and then increased.The residual tensile stress on the surface of the cladding layer under the optimal parameters was 59.5 MPa,the residual tensile stress at the joint was 50.7 MPa,and the residual compressive stress in the heat-affected zone was 4.3 MPa.(4)The cladding layer had the largest cracking tendency when electromagnetic field was not applied,after the current intensity was gradually increased,the number of cracks was reduced;When the electromagnetic parameter was 0.2 T+1200 A,no cracks appeared in the cladding layer,indicating that the electromagnetic field could effectively improve the cracking tendency of the coating.