Study On Microstructure And Properties Of Laser Cladding Gr/FeCoNiCrMo High Entropy Alloy Composite Coating

During the 14th Five Year Plan period and beyond,China will further promote"carbon peaking and carbon neutralization",strive to optimize the energy structure and promote the high-quality development of power industry.As a key part of the power industry,the performance of 17-4PH stainless steel,the main material of steam turbine blade,needs to be strengthened in order to improve the high-quality development of China’s power industry and promote energy conservation.As a new material rising in recent years,high entropy alloy has great application potential in wear resistance,high temperature resistance,corrosion resistance and so on.In order to improve the surface properties of 17-4PH stainless steel turbine blades,Gr/Fe Co Ni Cr Mo high entropy alloy composite coating with high hardness,wear resistance,corrosion resistance and water corrosion resistance was successfully prepared on 17-4PH stainless steel substrate by laser cladding technology.The main research contents are as follows:（1）Theoretical study on phase formation of Gr/Fe Co Ni Cr Mo high entropy alloy composite coating.Based on the high entropy alloy solid solution formation theory and intermetallic compound formation criterion,the solid solution type and intermetallic compound formation in Fe Co Ni Cr Mo high entropy alloy composite coating are speculated.On this basis,the phase composition evolution and element distribution in the solidification process of composite coating are simulated by Jmat Pro software.The regulation effect of Gr on the microstructure and properties of the coating was preliminarily explored.The results show that the phase composition of the composite coating after adding graphene is BCC phase,FCC phase,Laves phase and carbide.With the increase of the amount of graphene,the proportion of Laves phase gradually decreases and the proportion of BCC phase gradually increases.（2）Study on microstructure,properties and Gr strengthening mechanism of Gr/Fe Co Ni Cr Mo high entropy alloy composite coating.A single factor experiment on the amount of graphene was carried out to characterize the microhardness,wear resistance and corrosion resistance of the coating prepared under different amount of graphene.By analyzing its phase composition and microstructure,the strengthening mechanism of Gr was revealed.The results show that the composite coating after adding Gr is composed of FCC phase,BCC phase and M23C6 and M3C2 in-situ carbide.The in-situ carbide plays a role in improving the microhardness and wear resistance of the coating.When the amount of Gr is 0.4 wt%The average friction coefficient of the composite coating is 0.42,and the wear volume is 22.4*10^-3mm³,which is only 17%of the matrix.In addition,Gr promoted the grain refinement of the coating and inhibited the formation of Laves phase andσphase.which improved the distribution uniformity of Cr element and is conducive to the formation of passive film.（3）Effect of laser processing parameters on Microstructure and properties of Gr/Fe Co Ni Cr Mo high entropy alloy composite coating.Single factor experiments on laser power and scanning speed were carried out to characterize the microstructure and properties of the coatings prepared under different process parameters,and the range of process parameters was optimized.The experimental results show that when other conditions are certain,the microhardness,wear resistance and corrosion resistance of the coating increase first and then decrease with the increase of laser power or decrease of speed.When the laser power is 1600 W and the scanning speed is 9 mm/s,the performance of Gr/Fe Co Ni Cr Mo high entropy alloy composite coating is the best.（4）Optimization of process parameters of laser cladding Gr/Fe Co Ni Cr Mo high entropy alloy composite coating.The performance prediction model of composite coating is established through response surface experiment.On this basis,the process parameters are optimized by multi-objective genetic algorithm,and the Pareto optimal solution set of the process parameters of Gr/Fe Co Ni Cr Mo high entropy alloy composite coating prepared by laser cladding is obtained.The reliability and water resistance of the optimized process parameters are verified.The results show that the water corrosion resistance of the blade strengthened with composite coating can reach 7.15 times that of 17-4PH stainless steel blade.