Microstructure and Thermal Properties of Laser Cladding Ni-Cr-Mo Alloy Steel Coating

in this paper,two kinds of Ni-Mo-Cr coatings were laser-clad on the surface of H13 steel substrate by Nd³⁺:YAG laser.The chemical compositions of applied coatings were Ni₉Mo₂Cr_2.5Al_0.15Ti₁B₄Si₃Fe_78.4 and Ni₂Mo₂Cr_2.5Al_0.1Ti₁B₄Si₃Fe_85.4(mass fraction,w/%)respectively. Surface morphology,microstructure,phase composition,composition and thermal stability of the coating had been investigated by X-ray diffraction(XRD),metallographic microscope,scanning electron microscope(SEM),energy dispersive spectroscopy(EDS) and microhardness tester.The results show that the coatings of two Ni-Mo-Cr powders are metallurgically bonded to the matrix.The surface morphology presents uniform and dense fish scale.The main phases of the coating are γ-(Fe,Ni) solid solution,FeCr,α-Fe and NiCrFe equivalent compounds.Tthe coating region is composed of equiaxed grain,and the bonding region is composed of relatively coarse,columnar dendrites perpendicular to the bonding surface.The average microhardness of Ni-Mo-Cr coatings with 9% and 2% Ni addition are 650 HV_0.2 and 740 HV_0.2,respectively,which is about 2.8 to 3.2 times that of the matrix(230 HV_0.2). The thermal stability of the Ni-Mo-Cr coating is greatly improved compared to the H13 steel,and the coating is better when the Ni addition is 2%.