Research Of Laser Cladding High-entropy Alloy Coatings On 304 Stainless Steel Surface

304 stainless steel has excellent corrosion resistance,heat resistance and good processability,besides with its relatively low price,is widely used in production and life.However,its poor surface abrasion resistance limits the application in many fields..High entropy alloy,as a new alloy material,the unique multi-principle design concept makes it have excellent properties.In this paper,the surface modification technology of laser cladding is used to produce a high-entropy alloy coating with good morphology and uniform microstructure on the surface of 304 stainless steel.It will optimize the surface modification mothod of 304 stainless steel,and promote the further development of the field of high entropy alloy coating.In this paper,AlCoCrFeNiNb_x and AlCoCrFeNiNb_0.75+WC high entropy alloy coatings are prepared on the surface of 304 stainless steel by laser cladding.The phase structure and microstructure of the cladding layers are analyzed by X-ray diffraction,scanning electron microscope and electron probe.The microhardness of the samples are measured using a Vickers hardness tester,and the wear characteristics of coatings and the substrate are tested on a CFT-I multifunctional material surface performance tester.In addition,AlCoCrNiNb_x high entropy alloy coatings are further fabricated to study the effect of diffusion of Fe element in the stainless steel matrix on the microstructure and properties of the coatings.The results show that AlCoCrFe NiNb_x high-entropy alloy coatings and the matrix achieve good metallurgical bonding,and a good.quality molding is obtained.After the addition of Nb element,Nb riched Laves phase with hexagonal structure precipitate in AlCoCrFeNi alloy with single-phase BCC structure,and with the increase of Nb content,the amount of Laves phase increase.The microstructures of AlCoCrFeNiNb_x high-entropy alloy coatings evolve from a single phase（x=0）to hypoeutectic（0.25≤x<0.75）then to full eutectic（x=0.75）finally to hypereutectic（x>0.75）.When Nb content is 0.75,the microstructure is complete eutectic.The hardness of AlCoCrFeNiNb_x high-entropy alloy coatings increases with increasing Nb content.The hardness of AlCoCrFeNiNb_1.0 coating reaches a maximum of 826.6 HV,which is approximately 4 times that of the matrix.The high hardness results in a higher wear resistance of the coating than that of the substrate.The wear resistance of the coating increases first and then decreases as the Nb content increases.The AlCoCrFeNiNb_0.75 coating exhibits the best wear resistance.The study of AlCoCrNiNb_x high-entropy alloy coatings shows that Fe element in 304stainless steel matrix diffuses to the top of the coating,but the content is small,it makes little effect on the overall microstructure of the coating.Compared with the AlCoCrFeNiNbx series,the hardness of AlCoCr NiNb_x high-entropy alloy coatings are higher bringing microcracks.The addition of WC particles in the AlCoCrFeNiNb0.75 high entropy alloy with the best wear resistance reveals that a new intermetallic compound NbC phase appears in the coating,and its volume fraction increases with the increase of WC content;Eutectic microstructure in the coating gradually dissociated,BCC and Laves grow independently.Except for the coating with 20%WC,the hardness of the other coatings are higher than WC free coating,and when the WC content is 15%,the hardness reaches 828 HV,which is about 4 times that of the matrix.With the increase of WC content,the wear resistance of the coating increases first and then decreases.The wear resistance of the coating with 10%WC shows the best,which is about 1.8 times that of WC-free coating and 3.6 times that of matrix.