High-entropy alloys (HEAs), a relatively new class of materials, have attracted significant attention in materials science owing to their unique properties and potential applications. High entropy stabilizes the phase of a solid solution over a wide range of chemical compositions, yielding unique properties superior to those of conventional alloys. Therefore, this study analyzed the microstructure and electrochemical behavior of HEAs (Cantor) to evaluate their corrosion resistance, according to their manufacturing process (casting, cold rolling, and annealing). The microstructural morphologies and sizes were analyzed using electron backscatter diffraction. The electrochemical behavior was examined using open circuit potential measurements, electrochemical impedance spectroscopy, potentiodynamic polarization tests, and critical pitting temperature measurements using a potentiostat. The casting process formed a nonuniform microstructure (average grain size = 19 μm). The cold rolling process caused the formation of fine grains (size = 4 μm). A uniform microstructure (grain size > 151 μm) was formed after heat treatment. The corrosion resistance of the HEAs was determined from the passivation layer formed by Cr oxidation. These microstructural differences resulted in variations in the electrochemical behavior. Microstructural and electrochemical analyses are crucial because HEAs have diverse potential applications. Therefore, this study contributes to future improvements in HEA manufacturing processes.

High-entropy alloys (HEAs), such as the Cantor alloy, are considered for various structural applications owing to their excellent corrosion resistance and high strength at low temperatures, typically below −70 °C, including cryogenic conditions. However, during metalworking, introducing stresses and grain refinement can reduce the corrosion resistance of HEAs. Recrystallization heat treatment relieves these stresses and homogenizes the grain structure, thereby restoring their corrosion resistance and physical properties. However, inadequate heat treatment can result in a microstructure in which coarse and refined grains coexist; thus, the corrosion resistance is diminished and the physical properties are compromised. Therefore, a proper heat treatment is essential for achieving the desired corrosion resistance and mechanical properties of HEAs. In this study, a cold-rolled high-entropy Cantor alloy was subjected to heat treatment for various durations, and the conditions were analyzed. The microstructure and electrochemical behavior were examined. The results indicated that the grains coarsened after a heat treatment time of 5 min and the residual stresses decreased for 15 min. The potential increased from −0.20 to −0.09 V, whereas the resistance of the passive layer increased from 39 to 56 kΩ. These findings confirm that in the Cantor alloy, residual stress reduction and recrystallization begin after 5 min of heat treatment at 1100 °C, which contributes to the recovery of corrosion resistance. The corrosion resistance of the Cantor alloy can be effectively controlled through heat treatment. This underscores the importance of optimizing the heat treatment process in the manufacturing of Cantor alloys.

This study investigated the effects of the Mn content on the microstructure and superelastic properties of the Fe-Mn-Al-Ni alloys fabricated using direct energy deposition. As the Mn content increased from 36 at.% (36Mn) to 42 at.% (42Mn) with fixed Al and Ni contents, the fraction of the FCC-γ phase significantly increased in the as-built state. After six hours of homogenization at 1,200ºC, both the 36Mn and 42Mn alloys exhibited the BCC-α phase. In the results of cyclic compression test, both the 36Mn and 42Mn alloys exhibited superelastic properties. 42Mn, however, showed a superelastic displacement of approximately 3.6% at a maximum compressive displacement of 5%, which was lower than 4.0% of the 36Mn alloy. This appears to be due to the stabilization of the FCT-γ' phase caused by the high Mn content and the increase in permanent deformation caused by low critical slip stress. The results of this study indicate that alloy design that can promote reverse transformation into BCC-α upon the removal of stress by lowering the stability of the FCT-γ' phase while maintaining high critical slip stress is required to improve or maintain superelastic properties.