New directions in thermodynamic research of high-entropy alloys

Abstract

Turchanin M. A., Dreval L. A., Agraval P. G., Dovbenko A. I., Ilyenko S. M. New directions in thermodynamic research of high-entropy alloys // Herald of the DSEA. – 2019. – № 2 (46). – Р. 47–50.

A thermodynamic study of high-entropy alloys (HEA) of the Co–Cr–Cu–Fe–Ni system was performed. For this purpose, we used our own self-consistent base of thermodynamic parameters of the phases of ten two-component and ten three-component systems that are part of the studied system. Using this database and the CALPHAD method, the following were performed: the thermodynamic properties of four- and five-component equiatomic melts of the Co–Cr–Cu–Fe–Ni system were calculated at temperatures 1873 K and 1500 K; the phase transformations in a five-component system were modeled. The excess integral functions of mixing of four-component systems with copper and the Co–Cr–Cu–Fe–Ni system demonstrate positive deviations from ideality, which is due to positive copper–chromium pair interactions in the Co–Cr–Cu, Cr–Cu–Ni, Cr–Cu–Fe systems, copper–iron in the Cr–Cu–Fe, Co–Cu–Fe, Cu–Fe–Ni systems, copper–cobalt in the Co–Cr–Cu, Co–Cu–Fe systems. The behavior of the components in the Co–Cr–Fe–Ni system is close to ideal. A comparison of the values of thermodynamic functions calculated at 1873 K and 1500 K showed that a positive deviation from ideality of the excess thermodynamic mixing functions increased slightly with decreasing temperature and the magnitude of the ideal contribution to the Gibbs energy noticeably decreases. The results of modeling phase transformations demonstrate their similarity in four-component systems with copper and in the Co–Cr–Cu–Fe–Ni system. In four systems with copper (Co–Cr–Cu–Fe, Co–Cr–Cu–Ni, Co–Cu–Fe–Ni, Cr–Cu–Fe–Ni), the FCC solution separeted into FCC2 rich in copper, and FCC1 with a high content of chromium, cobalt, iron and nickel, and in the Co–Cr–Fe–Ni system, there is a high mutual solubility of the components. According to our calculations, the equiatomic Co–Cr–Cu–Fe–Ni alloy is two phase with the FCC+BCC structure. Practical recommendations have been developed on the choice of compositions of precipitation hardened HEA.