纵向磁场辅助激光熔覆GH3625镍基合金微观组织及摩擦、拉伸性能研究OA

To address the problems of coarse grains,elemental segregation,and compositional dilution commonly encountered in laser cladding of nickel-based alloys,this study investigated the regulatory effects of a steady longitudinal magnetic field on the molten pool flow behavior,microstructural evolution,and mechanical properties of the cladding layer,aiming to clarify the evolution laws of microstructure and properties under different magnetic field intensities.With GH3625 alloy powder as the cladding material and 304 stainless steel as the substrate,steady longitudinal magnetic fields with different intensities(0,50,100,150,and 200 mT)were applied during the laser cladding process.The macroscopic dimensions,grain morphology,grain orientation,grain boundary characteristics,elemental distribution,and phase constitution of the cladding layers were characterized by electron backscatter diffraction(EBSD),X-ray diffraction(XRD),scanning electron microscopy(SEM),and energy-dispersive spectroscopy(EDS).In addition,friction and wear tests and tensile tests were conducted to evaluate the wear resistance and tensile mechanical properties of the cladding layer.The results showed that,as the magnetic field intensity increased from 0 to 200 mT,the molten pool flow behavior gradually evolved from a single Marangoni convection mode to a thermoelectromagnetic convection-dominated mode and finally to a magnetic damping-dominated flow regime.Meanwhile,the microstructure of the cladding layer gradually transformed from columnar dendrites to equiaxed grains,grain orientations became increasingly randomized,and the proportion of high-angle grain boundaries increased significantly.The phase constituents remained unchanged under different magnetic field intensities and mainly consisted of a γ-Ni matrix,a Laves phase,and MC-and M23C6-type carbides.However,the magnetic field significantly regulated the morphology and distribution characteristics of the precipitated phases.At 200 mT,the Laves phase transformed from a continuous chain-like morphology under the magnetic-field-free condition into a discrete island-like distribution,and its area fraction decreased from 5.91%at 0 mT to 0.95%.The dilution ratio of the cladding layer initially increased and then decreased with the increase of the magnetic field intensity,reaching the minimum value of 14.57%at 200 mT.Similarly,the Fe content in the cladding layer first increased and then decreased,reaching its lowest value at 200 mT.Under a load of 15 N,the cladding layer fabricated at 200 mT exhibited the lowest coefficient of friction,the minimum wear track width of 901.05 μm,and the lowest wear mass loss of 4.3 mg,indicating the best wear resistance.The maximum elongation of 55.1%was achieved at 100 mT,whereas the ultimate tensile strength and yield strength reached their maximum values of 815 MPa and 538 MPa,respectively,at 200 mT.In conclusion,a steady longitudinal magnetic field can effectively regulate the macroscopic dimensions,grain microstructure,precipitate morphology,and elemental distribution of the cladding layer through the synergistic control of molten pool flow and mass transport behavior.An appropriate magnetic field intensity can suppress excessive dilution of substrate elements and weaken the formation of continuous brittle phases along grain boundaries,thereby significantly improving the wear resistance and tensile properties of the GH3625 cladding layer.Under the conditions investigated in this study,200 mT is identified as the optimal magnetic field intensity.