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 AlCrFe 2 Ni 2.1 , in a 0.5 M H 2 SO 4 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 AlCrFe 2 Ni 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 AlCrFe 2 Ni 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. • Electrochemical behavior of cost-effective AlCrFeNi HEAs with various microstructure characteristics was studied. • The AlCoCrFeNi 2.1 EHEA and cost-effective AlCrFeNi HEAs consist of (Co)CrFeNi-rich FCC and NiAl-rich (BCC)/B2 phases. • The AlCrFeNi 3.1 alloy has excellent passivation behavior, followed by the AlCoCrFeNi 2.1 and AlCrFe 2 Ni 2.1 HEAs. • High Cr/Al ratio of BCC/B2 phase in AlCrFeNi 3.1 alloy has potential formation of a thicker passive film.