Research On Hot Deformation Behavior,Microstructure Evolution And High Temperature Properties Of CoCrFeNiAl_0.1RE High Entropy Alloy

When compared to standard alloy materials,high entropy alloys are thought to offer an ideal mix of superior mechanical characteristics,high temperature resistance,and corrosion resistance,attracting a lot of interest from material scientists.As a result,studying the mechanical characteristics,microstructure,deformation mechanism,and high temperature resistance mechanism of high entropy alloy is critical from the standpoint of industrial use.Because of flaws like as coarse grain and irregular structure,as cast CoCrFeNiAl_0.1RE HEA has a low practical engineering application value.Through hot compression deformation experiments,the alloy’s constitutive model and hot working diagram can be built,and then the alloy’s optimal hot working process parameters may be tuned in conjunction with microstructure evolution.However,the material will experience several deformations during the forging and shaping process,resulting in a change in the material’s structure and composition as the deformation duration increases.As a result,it is vital to investigate the alloy’s thermal deformation behavior following significant structural changes in order to better regulate the material’s processing and forming.The mechanical characteristics of CoCrFeNiAl_0.1RE HEA reveal that the forged high entropy alloy has higher tensile mechanical properties than the cast high entropy alloy due to the fine grain strengthening effect.The yield strength was enhanced by 104 MPa,the tensile strength was increased by 208 MPa,but the elongation was marginally reduced by 2.13percent.The Arrhenius type constitutive equation of as forged CoCrFeNiAl_0.1RE HEA in the region of deformation temperature 1323-1473 K and strain rate 0.001 1 s^-1 was derived by the peak stress based on the hot compression experiment.As a result,a constitutive model for the HEA was developed in the temperature range of 1323-1473 K and the strain rate range of0.001 1 s^-1.The processing map demonstrates that in the high strain rate zone of forged CoCrFeNi Al0.1RE HEA,there are significant instability regions that should be avoided as much as possible during the machining process.The high temperature and high strain rate zones,as well as the extensive medium strain rate areas,are suitable hot working areas,with the greatest values（46 percent）at 1050℃/0.01 s^-1 and 1200℃/1 s^-1.Values are less than 30%in a wide variety of low strain rate zones,which is insufficient for the selection of hot operating parameters.The optimal hot deformation parameter of as cast high entropy alloy is in the medium temperature and moderate strain rate area,with a maximum value of 46%.This thesis investigates high temperature oxidation and hot corrosion experiments in order to better understand the high temperature characteristics of CoCrFeNiAl_0.1RE HEA.The high-temperature oxidation test temperatures were 800,900,1000,and 1100℃,respectively,while the hot corrosion test was conducted at 600,700,800,and 900℃in a mixed salt environment of 75% Na₂SO₄+25%Na Cl.During oxidation at higher temperatures,（Cr,Fe）₂O₃,Ni Fe₂O₄,CoCr₂O₄,and CoFe₂O₄ were mostly identified.The degree of damage to the oxide coating grew as the oxidation temperature climbed.At the same time,the oxide film’s outer layer was abundant in Cr,while the inner layer was deficient in Cr but abundant in other alloy elements.The created Cr₂O₃ layer might provide superior protection for the substrate and prevent further oxidation;in addition,XPS test findings confirmed the existence of distinct types of oxides.Cr₂O₃,NaCrO₂,Fe₃O₄,NiCrO₃,and AB₂O₄ spinel phase were the most common hot corrosion products.FCC matrix,on the other hand,could be identified owing to corrosion film damage;corrosion film cracking also increased as temperature climbed.However,throughout the corrosion process,S and Cl formed volatile compounds,and enriching S would exacerbate membrane falloff,making the associated chemicals difficult to detect.