Study On Microstructure Evolution And Corrosion Resistance And Wear Resistance Of CrCoNiNb_0.5Mo_xFe_y High Entropy Alloy Cladding Layers

High entropy alloy cladding layers with excellent corrosion resistance and wear resistance prepared by laser cladding technology can effectively solve the problems of surface corrosion and wear of marine engineering equipment in high salt,humid and heavy load environments,and provide an effective way for green corrosion and wear resistance strengthening modification of marine engineering equipment surface.In order to realize the enhancement of corrosion resistance and wear resistance of CrCoNiNb_0.5Mo_xFe_yhigh entropy alloy cladding layers,this paper studies the influence law and mechanism of laser energy density,Mo content and Fe content on the micro-structure,corrosion resistance,hardness and wear resistance of the cladding layers,and explores the appropriate process parameters of CrCoNiNb_0.5Mo_xFe_yhigh entropy alloy cladding layers.By adjusting laser energy density and cladding element composition,the corrosion and wear resistance of high entropy alloy cladding layers can be strengthened.The laser energy density has an important effect on the micro-structure evolution and mechanical,physical and chemical properties of CrCoNiNb_0.5Mo_0.25Fe high entropy alloy cladding layers.The temperature field simulation analysis of laser cladding CrCoNiNb_0.5Mo_0.25Fe high entropy alloy under different energy densities shows that with the increase of laser energy density,the maximum temperature during cladding increases,the cooling rate increases and the temperature gradient increases.The experimental results show that the CrCoNiNb_0.5Mo_0.25Fe high entropy alloy cladding layers prepared by different laser energy densities present incomplete eutectic micro-structure composed of FCC phase and Laves phase.The eutectic micro-structure can be promoted by increasing the laser energy density appropriately.The middle of CrCoNiNb_0.5Mo_0.25Fe high entropy alloy cladding layer prepared by laser energy density of 116.7 J·mm^-2presents anemometer eutectic structure with layer spacing of about 86 nm.The eutectic structure enhances the wear resistance while reduces the corrosion resistance of cladding layers to a certain extent.In the CrCoNiNb_0.5Mo_0.25Fe high entropy alloy cladding layers prepared by different laser energy densities,the cladding layer prepared by laser energy density of 116.7 J·mm^-2has closely packed eutectic structure and excellent wear resistance,but poor corrosion resistance.The increase of laser energy density enhances the dilution effect of Fe element in the substrate on the cladding layers and reduces the average hardness of the cladding layers.The cladding layer prepared by laser energy density of 100.0 J·mm^-2has the highest micro-hardness of 665.8 HV_1.0.The cladding layer prepared by laser energy density of116.7 J·mm^-2has the lowest wear rate.The increase of Mo content promotes the formation of Laves phase,thus affecting the mechanical properties and corrosion resistance of CrCoNiNb_0.5Mo_xFe（x=0.00,0.25,0.50,0.75,1.00）high entropy alloy cladding layers.CrCoNiNb_0.5Mo_xFe（x=0.00,0.25,0.50,0.75,1.00）high entropy alloy cladding layers consist of FCC phase and Laves phase.CrCoNiNb_0.5Mo_0.50Fe,CrCoNiNb_0.5Mo_0.75Fe and CrCoNiNb_0.5Mo_1.00Fe cladding layers have complete eutectic structure.The addition of Mo improves the corrosion resistance,hardness and wear resistance of the cladding layers by promoting the formation of Laves phase.In the prepared CrCoNiNb_0.5Mo_xFe（x=0.00,0.25,0.50,0.75,1.00）high entropy alloy cladding layers,CrCoNiNb_0.5Mo_0.75Fe cladding layer has the best corrosion resistance,and the CrCoNiNb_0.5Mo_1.00Fe cladding layer has the highest micro-hardness of 659.6 HV_1.0and the lowest wear rate of 0.125 mm³·N^-1·m^-1.In order to study the effect of Fe content in the cladding layers on the micro-structure evolution and properties of the cladding layers,CrCoNiNb_0.5Mo_0.75Fe_y（y=0.00,0.25,0.50,0.75,1.00）high entropy alloy cladding layers with different Fe content were prepared.By adjusting the actual Fe content of the cladding layers,optimize the structure and improve the wear and corrosion resistance of the cladding layers.The results show that with the decrease of Fe content in CrCoNiNb_0.5Mo_0.75Fe_y（y=0.00,0.25,0.50,0.75,1.00）high entropy alloy cladding layers,FCC phase decreases and Laves phase increases,and the eutectic structures with alternating FCC phase and Laves phase in the cladding layers disappears,and massive Laves phase grains are gradually formed.The decrease of Fe content reduces the content of FCC phase with poor corrosion resistance in the cladding layers,and increases the content of hard Laves phase,and gradually improves the corrosion resistance,hardness and wear resistance of the cladding layers.The CrCoNiNb_0.5Mo_0.75Fe_0.00cladding layer completely free of Fe in the cladding powder has the minimum corrosion current density of 1.436×10^-6A·cm^-2,the highest micro-hardness of 692.8 HV_1.0and the lowest wear rate of 0.105mm³·N^-1·m^-1.The passive regions of the CrCoNiNb_0.5Mo_0.75Fe_y（y=0.00,0.25,0.50,0.75,1.00）high entropy alloy cladding layers are higher than that of most high entropy alloys and stainless steels,which have stronger surface corrosion resistance passivation protection ability,laying a foundation for the extensive application of the high entropy alloy cladding layers in the corrosion protection field of marine engineering equipment.