Experimental investigation and thermodynamic re-assessment of the Mn–Nd binary system

Abstract

Fourteen Mn-Nd alloys were investigated experimentally by means of thermal analysis. The temperatures of the invariant reactions and liquidus in the Mn-Nd binary system were determined. Based on the experimental results obtained in the present work as well as the experimental data reported and the previous assessments in the literature, the Mn-Nd binary system was re-assessed thermodynamically using the CALPHAD method. The solution phases, including liquid, a-Mn, b-Mn, c-Mn, d-Mn, a-Nd and d-Nd, are modeled by the substitutional solution model, and their excess Gibbs energies are expressed with the Redlich-Kister polynomial. The intermetallic compounds, Mn 2 Nd, Mn 23 Nd 6 and Mn 17 Nd 2 , are treated as stoichiometric compounds. A set of self-consistent thermodynamic parameters obtained finally to describe the Gibbs energies of various phases in the Mn-Nd binary system can be used to reproduce well the reported phase equilibria and thermodynamic data.

Development of thermodynamic database of the Mn‐RE (RE = rare earth metals) binary systems

“…Phase equilibria of the Mn‐Ho binary system were studied experimentally, [41,47] and were calculated by Wang et al., [49] Kim et al., [20] and Wang et al [24] . According to the reported experimental data and calculations, five Mn‐RE (RE = La, Nd, Gd, Dy, and Ho) binary systems were reassessed in our group [21–24] . The calculated results are consistent well with the experimental data.…”

“…There are three stable intermetallic compounds, Mn 12 Tb, Mn 23 Tb 6 , and Mn 2 Tb in the Mn‐Tb binary system. It was observed that the reported experimental results [34] are not consistent with the new experimental data in the Mn‐RE (RE = Nd, Gd, Dy, and Ho) binary systems [22–24] . Therefore, it is reasonable the calculated Mn‐Tb binary phase diagram shows a slight deviation from the experimental data [34] .…”

“…In our previous work, [21–24] phase equilibria of the Mn‐RE (RE = La, Nd, Gd, Dy, and Ho) binary systems were redetermined experimentally. Therefore, the proposed temperatures of the invariant reactions were obtained in this work by mainly taking into account the systematic trend mentioned in Section 3.3 above and combining the formation temperatures of the Mn‐RE intermetallic compounds, [21–24] which are different from that proposed by Kim et al [19] …”

“…indicated that the results of the invariant reactions determined by Kirchmayr and Lugscheider [34] in the Mn‐Tb binary system are unreliable after comparing with the reported phase equilibria of the Mn‐Nd, Mn‐Gd, and Mn‐Dy binary systems. Furthermore, phase equilibria of the Mn‐RE (RE = Nd, Gd, Dy, and Ho) binary systems were studied experimentally in our previous work, [22–24] which shows that the invariant reactions in the Mn‐Tb binary system observed by Kirchmayr and Lugscheider [34] are not available. Okamoto [63] reviewed the Mn‐Tb binary system.…”

“…In our previous work, five Mn‐RE (RE = La, Nd, Gd, Dy, and Ho) binary systems were assessed using the substitutional solution model to describe the liquid phase [21–24] . The Mn‐La binary system was investigated by several authors [25–32] and thermodynamic calculations of this binary system were performed [18,21,33] .…”