Phase Stability in High-Entropy Alloys: The Role of Configurational Entropy

High-entropy alloys (HEAs) have been attracted the attention of many researchers and have exhibited excellent performance due to their structures. Many researchers take the view that the unique structure of HEAs is closely related to configurational entropy (S-mix). Hence, it is of great significance to assess the role of configurational entropy on the phase stability for designing HEAs. A model for calculating the S-mix of HEAs, including that containing interstitial atoms, has been proposed in this work. The results demonstrate that the true mixing entropy (S-T) deviates from the ideal mixing entropy, and is controlled by the mismatch of the atomic size and mixing enthalpy. Hence, the S-T of HEAs decreases with decreasing temperature, which reduces the stability of solid solutions. Moreover, introducing very different atoms, such as carbon, would exacerbate this trend. This means that it is still difficult to obtain high solid solubility for such atoms in HEAs even at high temperature, which is consistent with the experimental results. It is demonstrated that the role of entropy was reflected in the driving force of intermetallic compounds and the entropy-related diffusion coefficient. The work is helpful in understanding the effect of configurational entropy on the microstructure and properties of HEAs.