Study On Microstrcture And Properties Of Co-based Hea Composite Coating Prepared By Laser Cladding On H13 Steel

H13 hot die steel is a commonly used hot die steel.During servicing process,due to thermal erosion,surface failure will occur on the surface of the steel.It is necessary to perform surface modification on the surface to prolong its service time and ensure the quality.The high-entropy alloy has a series of excellent properties due to its unique"four major effects",such as high strength and hardness;excellent wear and corrosion resistance and good high temperature performance.Ceramic materials often have high strength,hardness and excellent high temperature performance.The metal-based ceramic composite material combines the advantages of metal and ceramic,and can further improve the surface properties of the material.In this thesis,a high-entropy alloy composite cladding layer of(Co₃₄Cr₂₉Ni₈Fe₈B₈)_100-xSi_x and different content of WC was prepared on the surface of H13 hot die steel by laser cladding process,and the microstructure and surface mechanical properties of high-entropy alloy and its composite cladding layer was studied.For the laser workstation in this subject,a four-factor three-level orthogonal test with current,pulse width,frequency and scanning speed as parameters was designed,and the microhardness and dilution rate on the top of the coating were selected as the evaluation criteria.Obtain the optimal process parameters:380A of laser current,4Hz of laser frequency,100mm/min of laser scanning speed and 6ms of pulse width.Under this process parameter,the coating had a higher top microhardness and a more appropriate dilution rate.X-ray diffractometer,field emission scanning electron microscope,optical microscope,Vickers hardness tester and friction and wear equipment were used to prepare the microstructure and properties of(Co₃₄Cr₂₉Ni₈Fe₈B₈)_100-xSi_x and high entropy alloy composite cladded layers.The results showed that:The laser cladded layers of(Co₃₄Cr₂₉Ni₈Fe₈B₈)_100-xSi_x were well formed,and the bonding with the substrate is metallurgical,the elements between the cladded layer and the substrate was well transited.The main phase composition in the coating is FCC solid solution phase and Cr B precipitation phase.As the atomic ratio of Si element increases,the microstructure of the top of the coating was more uniformly distributed,the intracrystalline area increased,and the intergranular eutectic precipitates decreased.The high-entropy alloy composite coating with different amounts of WC added was also well formed.The microstructure of the coating was evenly distributed without macrosegregation.The addition of WC significantly refines the grain on the top of the coating.WC was thermally decomposed during the cladding process and generates Cr₂₃C₆phase.The W element was mainly distributed in the columnar crystals in the middle and bottom parts of the coating.The increase of Si element content could effectively improve the microhardness of the coating.In the room-temperature wear test,the wear resistance of the coating with different Si content is better than that of the H13 steel substrate.With the increase of Si element content,the weight loss and friction coefficient at room temperature are improved combined to the substrate.The high temperature wear test also showed a similar pattern,Si element can effectively reduce oxidative wear.When X=7,the room-temperature and high temperature wear resistance of the coating was the best.The microhardness of the coating increased with the amount of WC,and could reach a maximum of about 3.5 times the microhardness of the substrate.The results of the room-temperature and high temperature wear test of the coating showed that the wear resistance of the coating increased first and then decreased as the amount of WC was added.When the amount of WC was 9 wt.%,the wear resistance of the coating was the best.