Prediction of Sm- (Co, Cu, Fe, Zr) binary alloys’ thermodynamic parameters by improved miedema model

Currently, the original Miedema mixing enthalpy model yields calculation results that exhibit some discrepancies when compared to experimental data. Therefore, improving the precision of the Miedema model is essential to advance its development and application in developing samarium–cobalt permanent magnet alloys. To address this issue, the enthalpies of mixing for Sm–(Co, Cu, Fe, Zr) binary alloys were calculated using the modified model. In addition, the mixing enthalpy (ΔH), excess entropy (SE), excess Gibbs free energy (GE), component activity (α) and binary Gibbs free energy of Sm–Co and Sm–Fe were calculated. The results indicate that the improved Miedema model more accurately matches the experimental values. Sm– (Co, Fe, Cu) binary alloys tend to form intermetallic compounds easily, whereas Sm–Zr does not. The ΔH, SE and GE of Sm-(Co, Fe) are negative, and the activity of each component shows a considerable negative deviation from Raoult’s law in contrast to that of an ideal solution. In the range of 1550 ∼ 1620 K, the Gibbs free energy of SmCo5 and Sm2Co17 reactions is negative with the Sm2Co17 phase being thermodynamically more stable than the SmCo5 phase.