Microstructure And Properties Of CoCrFeNiMo_0.2 High Entropy Alloy Induced By High Current Pulsed Electron Beam

Lately,high entropy alloys?HEAs?have become potential candidates for key components of agricultural machinery due to their high strength,high hardness and excellent corrosion resistance.However,high entropy bulk alloys have prominent problems such as coarse structure and severe element segregation,which greatly damage the properties and severely restrict the application of HEAs.High current pulsed electron beam?HCPEB?technology,as an advanced and environmentally friendly surface modification technology,can effectively regulate the microstructure and greatly improve the properties of the materials.In this paper,HCPEB technology was used to control the microstructure on the surface of CoCrFeNiMo_0.2 high entropy alloy prepared by vacuum arc melting and powder metallurgy,respectively.The formation and evolution of the phase structure,surface morphology,and composition distribution of the initial alloy and HCPEB irradiated samples were studied.Subsequently,the microhardness,abrasion behavior and electrochemical corrosion performance on the surface of the samples before and after HCPEB irradiation were tested,and the strengthening mechanisms of the surface properties of the material were analyzed and summarized.After HCPEB irradiation,the XRD analysis of the as-cast alloy and sintered samples showed that no new phase was formed on the surface,however,the surface of irradiated samples exhibited preferential orientation.Microstructure observations revealed that the defects such as pore network,unmelted particles,and component segregation on the surface of the initial alloys were eliminated by HCPEB,and the surface was remelted,showing a typical crater morphology and the crater density gradually decreased with the number of pulses increased.Due to the rapid melting,cooling and solidification processes,the composition of the irradiated surface was uniform,the grains were significantly refined,a dense remelted layer was formed and the thickness of which was gradually increased with the increase of HCPEB pulses.The TEM observations showed that a large number of nano-sized?phase particles were formed on the surface of the irradiated samples,and sub-structures such as subcrystals,high-density dislocations,dislocation cells,stacking faults,and twins were induced by HCPEB irradiation.After HCPEB irradiation,the microhardness on the surface of the as-cast alloys and sintered samples were significantly enhanced,and the microhardness values gradually increased with the increase of the number of pulses,which was mainly due to fine grain strengthening,diffusion strengthening and strain strengthening.The HCPEB irradiation remarkably improved the wear resistance on the surface of the original CrFeCoNiMo_0.2 high entropy alloy.The factor to improve the wear resistance was the precipitation of nano-scale?phases with extremely high hardness on the surface,these small particles not only improved the hardness on the surface,but also played a role in reducing friction.The electrochemical corrosion results revealed that the irradiated samples had higher corrosion potential and lower corrosion current density in 3.5 wt.%NaCl solution,which indicated that the corrosion resistance of the samples was significantly improved.A uniform and dense protective layer,high density grain boundary,and a large number of structural defects jointly promoted the growth of a continuous and stable oxide film,thereby improving the corrosion resistance on the surface of the material.