GPa level pressures on the microstructure evolution of eutectic high-entropy alloys CoCrFeNi(TiNb)0.325 and corrosion resistance

Abstract

In this study, high-pressure solidification (HPS) was used to systematically investigate the microstructure evolution and corrosion resistance of the designed eutectic high-entropy alloy CoCrFeNi(TiNb)_0.325 under ambient pressure, 4 GPa and 7 GPa. With increasing solidification pressure, the eutectic component points continue to move toward the upper left of the phase diagram, and the microstructure of the EHEA changes from eutectic under AP to hypereutectic at 4 GPa. Finally, the eutectic lamellar structure disappears under 7 GPa pressure, and the microstructure shows a divorced eutectic morphology. Mott–Schottky and XPS analyses revealed that the passivation film defect density of the HPS sample was lower than that of the other samples, but because the increase in the FCC/Laves phase spacing promoted pitting nucleation, the sample was difficult to repassivate, thus weakening the pitting corrosion resistance of the HPS sample. This work provides new insights into the relationships among pressure, microstructure, and corrosion performance.