Experimental investigation of the phase equilibria and thermodynamics properties of the Fe-TM-Ce systems
High saturation magnetization is obtained for compounds with light rare-earth metals. Rare-earth – transition metal compounds form an interesting group of magnetic materials and are important for making permanent magnets.
Re2Fe17-xTMx compounds (TM – transition metals) are of interest from the standpoint of the search for new high-energy materials for permanent magnet production. The partial substitution of TM for Fe can increase the Curie temperature and the saturated magnetostriction. In this project is aimed to experimental study, using SEM, EPMA, X-ray and DTA, of the phase equilibria in the Fe-TM-Ce systems. Due to lack of the experimental information on thermodynamic properties of the Fe-TM-Ce systems, this project is aimed also to experimental determination of enthalpy of formation, ΔHof, of intermetallic composition.
The enthalpies of formation of the ternary compound different compositions Fe13.3-11.0Mn3.7-6.0Ce2 (t1) were measured in the first time by solution drop calorimeter in an aluminium bath. The enthalpy of formations ∆Hof for t1 were measured as -(1.51-5.88) kJ/mol/atom.
The isostructural compounds Fe17Ce2 and Co17Ce2 (Zn17Th2-type structure, hR57-R-3m) were shown to form a continuous solid solution (Fe,Co)17Ce2 at the solidus temperature. The Laves phase Fe2Ce and Co2Ce (MgCu2-type structure, cF24-Fd-3m) also form a continuous solid solution (Fe,Co)2Ce at the solidus temperature.
The liquidus surface of the Fe-Co-Ce system is characterized by fields of primary crystallization of (γFe,Co), (δFe), (δCe), (gCe) and the binary-based phases (Fe,Co)17Ce2, (Fe,Co)2Ce, Co5Ce, Co19Ce5, Co7Ce2, Co3Ce and Co11Ce24. In the solidus surface five three-phase fields are present: (gCe) + (Fe,Co)2Ce + Co11Ce24, (Fe,Co)17Ce2 + (Fe,Co)2Ce + Co3Ce, Co5Ce + Co19Ce5 + Co7Ce2, (Fe,Co)17Ce2 + Co5Ce + Co7Ce2 and (Fe,Co)17Ce2 + Co7Ce2 + Co3Ce. The first three-phase field at the solidus surface results from an invariant eutectic four-phase equilibria LE ⇄ (gCe) + (Fe,Co)2Ce + Co11Ce24.
At 900 °C the liquid phase is stable in the Fe-Co-Ce system. The isothermal section at 900°C is characterized by five three-phase regions: (Fe,Co)17Ce2 + (Fe,Co)2Ce + Co3Ce, Co5Ce + Co19Ce5 + Co7Ce2, (Fe,Co)17Ce2 + Co5Ce + Co7Ce2, (Fe,Co)17Ce2 + Co7Ce2 + Co3Ce and (Fe,Co)17Ce2 + (aFe) + (gCo) plus the corresponding two-phase rg.