In Situ Preparation Of AlCoCrFeNi Mesentropic Alloy Coatings By Electroplating And Electron Beam Cladding

High entropy alloy is one of the hot materials in recent research.Its four effects make it have excellent thermal stability,good friction performance and high strength.At present,high entropy alloy coating preparation methods mainly include laser cladding,electron beam cladding,thermal spraying and magnetron sputtering technology,but these technical means have certain shortcomings,among which both laser cladding technology and electron beam cladding technology are high energy beam dilution rate,magnetron sputtering technology is suitable for the preparation of high entropy alloy thin films.However,there are some limitations in the coating thickness,and the coating prepared by thermal spraying has the disadvantage of poor bonding performance with the substrate.In order to overcome these shortcomings,high entropy alloy coating with better performance was prepared.In this paper,non-isoatomic ratio Al Co Cr Fe Ni intermediate entropy alloy coating was prepared by electroplating composite electron beam cladding.The microstructure of the coating was analyzed by scanning electron microscopy（SEM）,X-ray diffraction（XRD）and energy dispersive spectroscopy（EDS）.The hardness and friction and wear properties of the coating were tested by nano-indentation equipment,3D profiler and friction and wear testing machine.The influence of technical parameters of electroplating Co Ni alloy coating on the microstructure and properties of the coating was explored.The experimental results are as follows:（1）In order to reduce the dilution effect of the substrate on the coating during electron beam cladding,Co Ni coating was prefabricated on 304#stainless steel surface by electroplating technology.The effects of plating time and bath temperature on the thickness,surface roughness,deposition efficiency and hardness of the coating were investigated.The results showed that the thickness of Co Ni coating increased from 6.95μm to 28.35μm when the plating bath temperature was fixed at 60℃and the plating time was 30 min,60 min,90 min and 120 min respectively,indicating that plating time had a significant effect on the coating thickness.There are a few pores in the coatings at different plating time,and the pores in the coatings at 90 min are the least,the hardness is 591.9 HV,the deposition rate is 8.77 mg·cm^-2h^-1,and the microstructure and properties of the coatings are the best.The thickness of Co Ni coatings increased from 1.09μm to 6.95μm when the plating time was fixed at 30 min and the plating bath temperature was 30℃,40℃,50℃,60℃and 70℃.When the plating bath temperature was 70℃,the coating defects increased and even spalling.The deposition rate of the coating increased with the increase of bath temperature.Comprehensive analysis shows that the coating quality is the best when the bath temperature is 50℃.The distribution of Co and Ni in Co Ni coatings is uniform at different plating time and bath temperature,and the atomic ratios of Ni and Co are close to 3～4:1.（2）On the basis of electroplating experiments,a layer of Al and Cr slices were simultaneously deposited on the surface of Co Ni coating by electron beam cladding technology to form a non-isoatomic isoentropic alloy coating compared to Al Co Cr Fe Ni.The XRD results show that the upper phase of the coating is FCC+BCC,and the middle phase of the coating is a single BCC phase.The maximum hardness of the coating reaches 626.2 HV_0.1at 90 min,which is 3 times of the hardness of the substrate.The analysis of the friction and wear results of the coating at 30～120 min shows that the wear rate of the coating is 1.47×10^-4mm³/N·m,and the wear resistance is 3.5 times of that of the substrate.The wear mechanism of coating in 30～120 min is abrasive wear.Analysis of hardness and friction and wear properties of 4～10 m A coating shows that the wear resistance of 4 m A coating is the best,which is 1.37×10^-4mm3/N·m,which is 3.7 times higher than that of the substrate.The wear mechanism of the coating from 4 to 10 m A is abrasive wear.In the analysis of the hardness of4～10 m A coating,it is found that the hardness of 6 m A coating is the highest,and the average hardness is 943.7 HV,about 2.6 times that of the matrix hardness.