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Page 2 of 37 Ye et al. J Mater Inf 2023;3:15 https://dx.doi.org/10.20517/jmi.2023.08

the enthalpy of formation of the Fe-RE (apart from Fe-Y, Fe-Ce, Fe-Gd, and Fe-Dy) intermetallic compounds
become increasingly negative. The results provide a thorough set of thermodynamic parameters of thirteen Fe-RE
binary systems, which could serve as a sound basis for developing a thermodynamic database of Fe-RE-based alloy
systems.

Keywords: Fe-RE binary systems, Phase equilibria, Thermodynamic

INTRODUCTION
The intermetallic compounds made of the transition metal Fe and rare earth (RE) elements have been
[1-3]
studied extensively because of their excellent physical properties . For example, Fe RE compounds
2
17
exhibit large negative thermal expansion below the Curie temperature, which has numerous high-precision
technology and positioning instrument applications . Fe RE compounds, such as Terfenol-D plates (i.e.,
[4-6]
2
Fe Tb Dy compound), enable efficient energy and information conversion between electromagnetic and
1-x
2
x
mechanical energy . Furthermore, Fe RE compounds have maximum strain characteristics among giant
[7-9]
2
magnetostrictive materials [10,11] . Additionally, the intermetallic compounds made of RE elements, the
transition metal Fe, and a third light element B (e.g., Nd Fe B, Dy Fe B, and Tb Fe B) have excellent
2
2
14
14
14
2
magnetic properties as permanent magnets, widely used in various industries, including electronic
information, electrical machine, and medical equipment [12-17] . The reliable phase diagrams and
thermodynamic properties of the Fe-RE binary systems are essential to better understand the effect of RE
metals on the phase formation of the Fe-RE intermetallic compounds.
Konar et al. executed a systematic calculation of the Fe-RE binary systems by using a modified
quasichemical model to describe the liquid phase considering the reported experimental results [18,19] .
Although the calculated thermodynamic properties and phase equilibria of the Fe-RE binary systems were
in agreement with the experimental information, Konar et al. did not consider the heat capacity of Fe RE
2
and Fe RE phases (e.g., Fe Tb, Fe Dy, Fe Er, Fe Lu, Fe Lu , and Fe Y ) at low temperature (below 298 K)
2
2
2
17
17 2
2
2
2
17
in their calculations . Moreover, to ensure model compatibility inside the thermodynamic database in the
[19]
Fe-RE-based systems. The description of the liquid phase reported by Konar et al. [18,19] needs to be revised to
match thermodynamic calculations of the B-RE binary systems in our previous work [20-24] . In our earlier
work, we also assessed the Fe-RE (RE = La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, and Tm) binary systems [25-29] . In
addition, the Fe-RE (RE = Pm, Eu, and Yb) binary systems have not been assessed because of a lack of the
experimental data, while the Fe-Y binary system was investigated through the experimental determination
and thermodynamic calculations .
[19]
This study focuses on the Fe-RE (RE = Er, Lu, and Y) binary systems by the CALPHAD method in
consideration of experimental results and previous calculations. To improve our previous calculations of the
Fe-RE (Tb and Dy) binary systems , the Gibbs energies of intermetallic compounds Fe Tb and Fe Dy were
[27]
2
2
modified to eliminate the artificial break point in their heat capacity curves that appear in the earlier work.
By combining our present evaluations with previous optimizations [25-29] , we provide a comprehensive
discussion of phase equilibria and thermodynamic characteristics of the Fe-RE binary systems.
LITERATURE INFORMATION
Fe-La and Fe-Ce
Several studies have experimentally investigated the Fe-La binary phase diagram [30-33] . These studies
identified three peritectic reactions and one eutectic reaction, but stable intermetallic compounds were not
observed. In addition, the thermodynamic properties in liquid Fe-La alloys were measured [34,35] .