Melting behavior and globular microstructure formation in semi-solid CoCrCuxFeNi high-entropy alloys

Abstract

High-entropy alloys can be compelling raw materials for semi-solid applications. In the present study, the influence of the Cu content on the melting behavior and semi-solid microstructure of CoCrCuxFeNi (x = 0, 1, 2, 3) alloys was investigated. Arc-melted samples were cross-rolled at room temperature and then isothermally treated at 1175 °C in the semi-solid state for 300 s. Microstructural characterization showed that the alloys containing Cu were formed by two fcc phases. Notably, the increase in Cu content also led to an increase in the volumetric fraction of the Cu-rich phase. During solidification, this phase, which is the last to form, nucleates and epitaxially grows on the Cu-lean phase. All the studied CoCrCuFeNi alloys exhibited the same melting behavior. The Cu-rich phase melts at approximately 1120 °C, whereas the Cu-lean phase melts at approximately 1350 °C, providing a suitable processing temperature range of more than 200 °C. The semi-solid microstructures were considerably refined and globular regardless of the alloy composition, being suitable for semi-solid processing. Furthermore, each fcc phase exhibited roughly the same composition under the different processing conditions. The Cu content in the Cu-lean phase was approximately 10 at.%, while Co, Cr, Fe, and Ni were in an approximately equiatomic ratio. Meanwhile, the Cu content was between 80 at.% and 86 at.% in the Cu-rich phase. The isothermal treatment of the CoCrCu3FeNi alloy at a higher temperature (1300 °C) only caused the globules to coarsen. In conclusion, this work showed that these alloys can be potential candidates for semi-solid processing