Microstructure characterization and corrosion behavior of Alx(CoCrFeNi)100−x (x = 0, 5, 10, 15, 20) high entropy alloys in 0.5 M H2SO4 solution.

Although the mechanical properties of CoCrFeNi system high entropy alloys (HEAs) could be enhanced with the increase of Al content, it is inevitable to produce a gradual transformation of multiphase microstructure with chemical segregations. It will lead to the change of work function and the appearance of localized corrosion. The present work investigates the correlation between the corrosion behavior and the microstructure of Al x (CoCrFeNi) 100−x (x = 0–20) HEAs in 0.5 M H 2 SO 4 solution by immersion test, electrochemical measurement, SKPFM and SEM. The microstructure of CoCrFeNi system HEAs with increasing the content of Al has been transformed from single FCC phase to mixture of FCC and BCC duplex phases, and then to BCC phase. The detected value of work function gradually decreases with Al addition. The addition of a little amount of Al which retains the single FCC phase structure is beneficial to improve the corrosion resistance of Al-containing CoCrFeNi system HEAs, and the addition of excessive Al elements which promotes the formation and growth of BCC phase weakens the corrosion resistance of Al-containing CoCrFeNi system HEAs. • The relationship between the microstructure and corrosion resistance of Al x (CoCrFeNi) 100−x was systematically studied. • The microstructure of Al x (CoCrFeNi) 100−x changes from single FCC phase to FCC + BCC, and then to BCC phase. • Little Al addition without phase change improves the corrosion resistance, while excessive Al addition weakens. [ABSTRACT FROM AUTHOR]