Research On Microstructure Of CoCrFeNiAl High Entropy Alloy After Rapid Cooling

High entropy alloys are formed by mixing five or more than five different elements with equal molar ratio or approximate molar ratio.Its good thermodynamic stability gives it high temperature strength,wear resistance,corrosion resistance and oxidation resistance.Therefore,high entropy alloy has a good application prospect and potential.The accelerated cooling rate will improve the microstructure and improve the properties of the alloy.In this paper,the high entropy alloy was irradiated by strong current pulse electron beam and the band rejection treatment.The effect of rapid cooling on the microstructure and properties of high entropy alloy was studied.The microstructure and properties of high entropy alloy Co Cr Fe Ni Al after electron beam irradiation were analyzed.The results of XRD show that the phase structure in the modified layer is still BCC single-phase solid solution structure after HCPEB irradiation,and there is no FCC phase structure,the diffraction peak position of the modified layer is offset,and the internal microcosmic residual stress is found.The results of scanning electron microscopy(SEM)show that after HCPEB irradiation,the surface of the alloy appears the melt pit and the micro crack,the thickness of the modified layer.The corrosion resistance of the modified layer is much stronger than that of the matrix at about 5 microns.The microstructure in the modified layer is granular,fine and uniform,and the size of the particles is about 100 nanometers.With the increase of the number of pulses,the surface re-melting is more full and the thickness of the modified layer changes little,but the particles in the modified layer are even smaller and even,The shape is more regular and round,and the results of transmission electron microscopy(TEM)show that after electron beam irradiation,the nanocrystalline crystal structure and the ordered BCC phase structure appear in the modified layer.The fine dispersion phase is distributed in the modified layer,and the dispersion phase size is about 20 nanometers,which is the B2 phase.At the same time,there are lots of dislocations in the modified layer,which indicates that there is a large thermal stress in the modified layer during cooling.After electron beam irradiation,the microhardness decreased slightly,the hardness value was about 530 HV,and the pulse times had little effect on the surface hardness.The microstructure and properties of high entropy alloy Co Cr Fe Ni Al banded samples after strip treatment was analyzed.The XRD results show that the diffraction peak of the BCC phase is still the same as that of the matrix,and the scanning electron microscope(SEM) results show that after the strip treatment,the equiaxed grains are formed in the strip samples,the grain size is between 1-6 microns,and the second phase is dispersed in the grains,and the grains on the contact surface with the copper roller are fine and uniform,and the speed increases,and the microstructure is refined.The transmission electron microscopy(TEM)results show that the microstructure of the high entropy alloy Co Cr Fe Ni Al is refined at a high cooling rate and the microstructure of the microstructure is formed at a higher cooling rate.This structure is still a single phase solid solution structure of BCC based on the B2.After the treatment,the microhardness increased slightly to 699.7HV,and the change of rotational speed had little effect on hardness.