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

Abstract

Abstract At present, the calculation results of the original Miedema mixing enthalpy model are still somewhat different from the experimental results. Therefore, it is necessary to improve the calculation accuracy of the Miedema model to promote the development of the Miedema model and its application in the design of samarium-cobalt permanent magnet alloys. To solve this problem, the enthalpies of mixing of Sm- (Co, Cu, Fe, Zr) binary alloys were calculated in this paper by using the modified model. The mixing enthalpy (DH), excess entropy (SE), excess Gibbs free energy (GE), component activity (α) and binary Gibbs free energy of Sm-Co, Sm-Fe were calculated. The results show that the improved Miedema model can better match the experimental values. Sm- (Co, Fe, Cu) binary alloys are easy to generate intermetallic compounds. And Sm-Zr is difficult to form intermetallic compounds. The DH, SE and GE of Sm- (Co, Fe) are negative, and there is a large negative deviation from Raoult's law for the activity of each component compared to the ideal solution. The Gibbs free energies for both SmCo5 and Sm2Co17 precipitation reactions are less than zero in the temperature range between 1550 and 1620 K. The Sm2Co17 phase is thermodynamically more stable than the SmCo5 phase.