The Microstructure And Corrosion Resistance Of Two High Entropy Alloys

High entropy alloy（HEA）possesses excellent corrosion resistance and becomes the research hotspot of corrosion,but the correlation between the microstructure and macroscopic corrosion resistance is still not clear.In this paper,Co Cr Cu_0.1Fe Mo Ni HEA and（Fe Co Ni）₆₀Al₁₅Cr₂₅HEA were used as the research material,the microstructure of HEAs was characterized by using X-ray diffraction（XRD）and scanning electron microscopy（SEM）.Corrosion behavior of HEAs in 0.5 M Na Cl,0.5 M Na OH,0.5 M H₂SO₄solution was investigated by electrochemical and immersion test.The passive film formed on the surface of HEAs was analyzed by using X-ray photoelectron spectroscopy（XPS）.The correlation among the compositions and microstructure of HEAs,composition of passive film and corrosion behavior was clarified.The results showed that Co Cr Cu_0.1Fe Mo Ni HEA was composed of island-like and dendritic structure,the island-like and dendritic structure were composed of Mo-Cr richμphase,the inter-dendritic structure was composed of Cu rich FCC1 phase and Fe-Ni rich FCC2 phase.（Fe Co Ni）₆₀Al₁₅Cr₂₅HEA exhibited a columnar dendritic structure,the main phase of columnar dendrite was Ni-Al rich BCC phase,and the inter-dendritic structure was composed of Fe-Co-Cr rich FCC phase.During the corrosion,the Cu rich phase and Fe-Ni rich phase in Co Cr Cu_0.1Fe Mo Ni HEA were prone to dissolve preferentially,while the Ni-Al rich phase in（Fe Co Ni）₆₀Al₁₅Cr₂₅HEA tended to corrode preferentially.The electrochemical results showed that the corrosion behaviors of Co Cr Cu_0.1Fe Mo Ni and（Fe Co Ni）₆₀Al₁₅Cr₂₅HEA in acid,neutral and alkali systems were inconsistent.In 0.5 M Na Cl and Na OH solutions,（Fe Co Ni）₆₀Al₁₅Cr₂₅HEA possessed lower corrosion current density and higher polarization resistance of passive film（R_p）,thus the corrosion resistance of（Fe Co Ni）₆₀Al₁₅Cr₂₅HEA was superior to that of Co Cr Cu_0.1Fe Mo Ni HEA.However,the corrosion resistance of Co Cr Cu_0.1Fe Mo Ni HEA in 0.5 M H₂SO₄solution was better.The results of immersion experiments showed that the value of R_pfor HEAs in 0.5 M Na Cl and 0.5 M Na OH solutions both increased with the increase of immersion time,indicating that the improvement of protective ability for passive film.Compared with Co Cr Cu_0.1Fe Mo Ni HEA,the value of R_pfor（Fe Co Ni）₆₀Al₁₅Cr₂₅HEA was higher when the immersion time was the same,indicating greater corrosion resistance of（Fe Co Ni）₆₀Al₁₅Cr₂₅HEA.The value of R_pfor Co Cr Cu_0.1Fe Mo Ni HEA in 0.5 M H₂SO₄solution was higher and increased with the extension of immersion time,indicating that the corrosion resistance of Co Cr Cu_0.1Fe Mo Ni HEA was better.The main corrosion-resistant element of the above HEAs was Cr,which can form a protective film of Cr₂O₃,and less protective film of Cr（OH）₃.Therefore,the value of Cr₂O₃/（Cr+Cr（OH）₃）can be used to evaluate the corrosion resistance of HEAs.XPS analysis results showed that the value of Cr₂O₃/（Cr+Cr（OH）₃）for HEAs in 0.5 M Na Cl and 0.5 M Na OH solutions increased with the extension of immersion time,indicating that the protective ability of passive film improved;compared with Co Cr Cu_0.1Fe Mo Ni HEA,the value of Cr₂O₃/（Cr+Cr（OH）₃）for（Fe Co Ni）₆₀Al₁₅Cr₂₅HEA was higher and exhibited greater corrosion resistance.In 0.5 M H₂SO₄solution,the value of Cr₂O₃/（Cr+Cr（OH）₃）for Co Cr Cu_0.1Fe Mo Ni HEA was higher and increased with the prolongation of immersion time,indicating that the corrosion resistance of Co Cr Cu_0.1Fe Mo Ni HEA was superior,differed from（Fe Co Ni）₆₀Al₁₅Cr₂₅HEA.