Effect Of Heat Treatment On Microstructure And Performance Of CoCrFeNiMn（Al₂O₃）_x Coating

High entropy alloys have been highly valued by researchers since they were proposed by scholars in 2004.After more than ten years of research,the properties of high-entropy alloys are also well known.For example,by changing the principal elements of different elements in the alloy,good properties can be obtained.Strength,hardness,plasticity,wear resistance,corrosion resistance and high temperature stability.There are also scholars adding ceramic phase nanoparticles to high-entropy alloys.This kind of high entropy alloys contribute to the change of the mechanical properties of the matrix due to the occurrence of lattice distortion.Compared with light alloys such as magnesium and aluminum or even steel,it can effectively improve the strength of the material,Hardness and wear resistance.Because this kind of material has various good properties at the same time,it has good development prospects in many different industries.In this paper,three kinds of CoCrFeNiMn（Al₂O₃）_x high-entropy alloy coatings with different Al₂O₃ content were prepared by plasma spraying technology.The three high-entropy alloy coatings were heat-treated at five different temperatures and carried out at 700℃.High temperature oxidation experiment.Subsequently,X-ray diffractometer,scanning electron microscope,energy spectrometer,and Vickers hardness tester were used to study the changes in structure and hardness of Al₂O₃ high-entropy alloy coatings with different compositions,different treatment temperatures and high-temperature oxidation,and are compared the difference in its organization and performance.The experimental results showed that the unheated CoCrFeNiMn（Al₂O₃）_x high-entropy alloy coatings all had a single FCC structure,and their structure is lamellar.With the increase of Al₂O₃ content,the hardness of the coating gradually increases.After the heat treatment,the CoCrFeNiMn（Al₂O₃）_x coating is still a single FCC structure,the coating and the substrate were well bonded,no cracks are found in the coating,and multiple oxides appear in the structure,and the hardness is less than that without heat treatment.The coating had increased.When the heat treatment temperature was 700℃,the dark gray lamellar layer enriched with Ni,Cr and O elements in the CoCrFeNiMn（Al₂O₃）_x（x=0,0.25,0.5）coating and the light gray layered structure enriched with Co and Fe elements.The distribution is the most uniform in the coating,and the average hardness reaches the highest value after heat treatment,which were 516.8HV,543.6HV and 560.7HV,respectively.Subsequently,as the heat treatment temperature continued to increase,the lamellar structure gradually began to diffuse,and the hardness began to decrease.After 50 hours of high temperature oxidation at 700°C,Cr O,Ni Mn₂O₄.appeared in the coating.The oxidation weight gain of CoCrFeNiMn（Al₂O₃）_x（x=0,0.25,0.5）high-entropy alloy coatings decreases with the increase of Al₂O₃ content,and the average oxidation weight gain rate of each group of coatings（x=0,0.25,0.5）respectively 0.081 g/（m²·h）,0.087g/（m²·h）and 0.066 g/（m²·h）.The FCC structure has not changed with the increase of time,and there are no defects such as cracks in the coating after high temperature oxidation.