Microstructure And Properties Of Laser Cladding FeCoNiCuAlNbx High Entropy Alloy Coating

304 stainless steel is usually used to manufacture valves because of its good cutting performance,excellent corrosion resistance and relatively low price.However,due to its low hardness,poor wear resistance and so on,it often leads to the leakage of in-service valves,which will undoubtedly bury a huge potential safety hazard,and ultimately not only the loss of property,but also seriously endanger people's lives.High entropy alloy coating on the surface of the substrate can effectively improve the hardness,wear resistance and corrosion resistance of the valve,reduce the replacement times,save the cost and improve the safety.The FeCoNiCuAlNb high entropy alloy coating was coated on 304 stainless steel surface by laser cladding technology.The surface morphology and microstructure of the cladding layer under different traveling speed and output power were compared,and the optimal parameters are 200 W and 420mm/min.The coating surface is compact and beautiful fish scale,bright and without ablation.There is a good metallurgical bonding between the substrate and the cladding layer,and there are no obvious cracks,pores,inclusions and other defects in the cross section of the cladding layer.The average hardness of the cross section of the cladding layer is 584 Hv,which is about 3.34 times of that of the substrate.The wear resistance and corrosion resistance of the cladding layer are also the best.FeCoNiCuAlNbx(molar ratio of x = 0.25,0.5,1.0)high entropy alloy coating were prepared with the optimal process parameters.With the increase of Nb content,the thickness of the cladding layer has no obvious change,which is about 500?m.The dilution ratio of cladding layer is about 15%.The microstructure of the cladding layer is composed of fine and uniform equiaxed grains at the top,coarse equiaxed grains at the middle and columnar grains with preferential orientation at the bottom.The coating has BCC,FCC and Laves phases,and the Laves phase content in the coating increases with the increase of Nb content.With the increase of Nb content,the hardness,wear resistance and corrosion resistance first increase and then decrease.FeCoNiCuAlNb0.5has the highest hardness and the best wear resistance and corrosion resistance.After double-layer cladding,the surface of the coating appears oxidation and burning loss.The first layer of cladding layer has good metallurgical bonding with the substrate.The second layer of cladding layer has poor bonding with the first layer of cladding layer.It not only has a large area of spalling,but also has cracks in the middle of the cladding layer.The microstructure of the first layer shows that there are more equiaxed grains in the middle region,and columnar grains near the bottom of the substrate and at the bottom of the second layer.The top of the second layer is mainly fine equiaxed crystal,and the bottom is columnar crystal growing along the heating direction.Specifically,laves gather and grow,and appear honeycomb grid in the middle region.In the bottom region,due to the influence of temperature gradient,it elongates along the heating direction,becoming more dense,which presents a narrow honeycomb shape.The average hardness of the cross section of the double-layer cladding layer is 614.3 Hv,which is about 3.13 times that of the substrate,and the maximum hardness can reach 715.4 Hv.Compared with single-layer cladding,the improvement of hardness and corrosion resistance is small.