Thermodynamic analysis of phase equilibria in the Nd-Fe-Cu ternary system

A thermodynamic assessment of the Nd-Fe-Cu system was attempted using the CALPHAD method, to clarify an effect of Cu addition to the permanent magnets based on Nd₂Fe₁₄B phase. The regular solution model was applied to liquid phase and solid solutions. Intermediate compounds were described as stoichiometric phases. The formation enthalpy of σ(Nd₆Fe₁₃Cu) phase was evaluated using the first-principles calculation. The result was introduced to the optimization process with some experimental phase boundary data. In the calculated liquidus projection of the ternary system, it is characteristic that the two-phase separation of the liquid phase exists between Fe-rich and (Nd, Cu)-rich regions. The ternary eutectic reaction E1:( L)⇔βNdCu+(αNd)+σ occurs in the Nd-rich region and the reaction temperature is estimated about 508.6?.