Static transverse magnetic field assisted laser cladding of nickel alloy GH3625 for enhancing its microstructure, microhardness, friction and wear properties on 304 stainless steel substrate

Abstract

At present, the microstructure and properties of laser-clad GH3625 alloy are mainly controlled by adjusting the cladding processing parameters. However, regulation of the fluid flow in the melt pool requires more than adjusting the laser cladding parameters alone, making it a significant challenge to control the cladding layer structure. In this study, an approach for enhancing the microstructure and properties of laser-cladded GH3625 on a non-magnetic 304 stainless steel substrate is investigated by applying an auxiliary static transverse magnetic field in the coaxial powder-feed cladding process. The magnetic field strength was varied between 0–200 mT. The macro-microstructure, elemental composition, phase structure, hardness and friction and wear properties of the cladding layer were analysed by SEM, EDS and XRD. The role and action mechanism of the applied static magnetic field in modulating the fluid flow of the melt pool were investigated. The electromagnetic braking and thermoelectric magnetic effects are discussed to for their influences on the melt pool formation and characteristics. Under the influence of electromagnetic braking, the molten pool morphology is regulated and the dilution rate of the cladding layer decreases. On the other hand, under the action of the static magnetic field, Seeback effect is generated causing thermoelectric circulation at the top of the dendrites, and resulting in thermoelectric magnetic force, which leads to irregular dendrite growth and promoted the grain refinement. The thermo-electric magnetic force strengthens the solute transport, and promotes the precipitation and uniform distribution of the strengthening phases such as the γ’ phase and carbides, and thereby enhancing the hardness and wear resistance of the cladding layer. At the magnetic induction intensity of 120 mT, the highest hardness and the lowest friction coefficient were obtained at 300 HV_0.2 and 0.34 respectively. Higher static magnetic field leads to higher thermo-electric magnetic force, and its blocking effect on grains becomes stronger and induces a large area of annular bands. The annular band structure becomes increasingly more significant in truncating the original phase. The content of Fe element in the cladding layer increases, resulting in Fe elemental segregation.