Abstract
AlCoCrFeNiZrx (x = 0, 0.1, 0.2, 0.3, and 0.5) high-entropy alloys (HEAs) were prepared by a non-consumable vacuum arc melting technology, and the microstructure and corrosion behavior were investigated by XRD, SEM, immersion tests, and electrochemical measurements. The results indicate that galvanic corrosion of the AlCoCrFeNiZrx alloys occurred in 0.5 M H2SO4 solution, and only 0.1 mol of the added Zr could greatly improve the corrosion resistance of the alloys. The corrosion properties of the AlCoCrFeNiZrx HEAs had similar change tendencies with the increase in the Zr content in the immersion tests, potentiodynamic polarization measurements, and electrochemical impedance analysis, that is, the corrosion resistance of the AlCoCrFeNiZrx alloys in a 0.5 M H2SO4 solution first increased and then decreased with the increase in the Zr content. The Zr0.1 alloys were found to have the best selective corrosion and general corrosion resistance with the smallest corrosion rate, whereas the Zr0.3 alloys presented the worst selective corrosion and general corrosion resistance with the highest corrosion rate from both the immersion tests and the potentiodynamic polarization measurements.
Highlights
high-entropy alloys (HEAs) or multi-principal element alloys (MPEAs) were first defined as alloys composed of five or more principal elements in equimolar ratios and with simple average crystal structures such as face-centered cubic (FCC), body-centered cubic (BCC), and CsCl; the definition was expanded to alloys in which the principal elements each had a concentration of 5–35 at. %, and the alloys could contain minor elements in concentrations below
Many researchers have contributed their efforts to understanding the fabrication, composition, microstructure, and properties of more than 400 HEAs to date [5,6,7,8,9,10,11,12], where the CoCrFeNi system HEAs have been heavily researched, and many studies in the literature have focused on improving the corrosion resistance of CoCrFeNi system HEAs through the addition of other alloy elements, such as Al, Mn, Mo, Cu, and Ti [13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29]
Kao et al [14] investigated the electrochemical passive properties of AlxCoCrFeNi alloys by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and weight loss tests, indicating that a higher amount of Al in AlxCoCrFeNi alloys was harmful to the corrosion resistance in a 0.5 M H2 SO4 solution at temperatures exceeding 27 ◦ C; similar results for the Al content were obtained by Lee et al regarding the corrosion behavior of AlxCrFe1.5MnNi0.5 alloys in aqueous environments, where an increased proportion of Al resulted in a higher general corrosion susceptibility of the alloys in a 0.5 M H2 SO4 solution, and the pitting potentials of Al0.5CrFe1.5MnNi0.5 HEAs were significantly lower than those of Al-free CrFe1.5MnNi0.5 HEAs in a 1 M NaCl solution [15]
Summary
Due to their excellent functional and mechanical properties as well as being highly promising candidates for industrial applications [1,2,3,4], high-entropy alloys (HEAs) or multi-principal element alloys (MPEAs) have caused widespread attention in the materials science and engineering fields. Many researchers have contributed their efforts to understanding the fabrication, composition, microstructure, and properties of more than 400 HEAs to date [5,6,7,8,9,10,11,12], where the CoCrFeNi system HEAs have been heavily researched, and many studies in the literature have focused on improving the corrosion resistance of CoCrFeNi system HEAs through the addition of other alloy elements, such as Al, Mn, Mo, Cu, and Ti [13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29]. The corrosion behavior of the CoCrFeMnNi family HEAs was evaluated in a CO2 -containing 3.5 wt %
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