Exploring the corrosion behavior of cost-effective AlCrFeNi high-entropy alloys with various microstructure characteristics in sulfuric acid environment

Eutectic high entropy alloys (EHEA) such as AlCoCrFeNi_2.1 exhibit unique mechanical properties, including higher strength and ductility compared to single-phase solid solution high entropy alloys (HEAs). However, their high Co content limits their engineering applications. In this work, the corrosion behavior of cost-effective AlCrFeNi HEAs, specifically AlCrFeNi_3.1 and AlCrFe₂Ni_2.1, in a 0.5 M H₂SO₄ environment is systematically studied by electrochemical methods. Furthermore, the results are compared with those of AlCoCrFeNi_2.1 EHEA. The findings demonstrate that both the AlCoCrFeNi_2.1 EHEA and cost-effective AlCrFeNi HEAs, namely AlCrFeNi_3.1 and AlCrFe₂Ni_2.1, consist of (Co)CrFeNi-rich face-centered cubic (FCC) and NiAl-rich body-centered cubic (BCC)/B2 phases. The AlCrFeNi_3.1 alloy has excellent passivation behavior, followed by the AlCoCrFeNi_2.1 and AlCrFe₂Ni_2.1 HEAs. The high Cr/Al ratio of the BCC/B2 phase in the AlCrFeNi_3.1 alloy decreases the formation of Al hydroxides/oxides in the complex passive film, which enhances passivation and leads to a thicker passive film on the alloy surface. Specifically, the Al hydroxides/oxides reduce corrosion resistance, while Cr serves a crucial protective function. These insights significantly enhance our understanding of the electrochemical behavior of cost-effective AlCrFeNi HEAs subjected to environment-induced degradation, providing valuable guidance for the development of innovative protective materials in engineering applications.