Fe-P-Ti (Iron-Phosphorus-Titanium)

Abstract

The previous review of the experimental data on this ternary system by [1988Rag], based on mainly on the work of [1959Vog] and[1965Kan], presented a liquidus projection, an isothermal section at 25°C and a reaction scheme for the Fe-FeP-Ti region. Recently, [2006Oht] made a CALPHAD-type thermodynamic analysis of the entire system, incorporating first-principles energy calculations. Binary SystemsThe Fe-P phase diagram [2006Oht, Massalski2] has the following compounds at ambient pressure: Fe 3 P (D0 e , Ni 3 Ptype tetragonal), Fe 2 P (C22, Fe 2 P-type hexagonal), FeP (B31, MnP-type orthorhombic), FeP 2 (C18, FeS 2 -marcasite type orthorhombic), and FeP 4 (monoclinic). There are two intermediate phases in Fe-Ti system: Fe 2 Ti (C14, MgZn 2 -type hexagonal) and FeTi (B2, CsCl-type cubic). The computed P-Ti phase diagram [2006Oht] shows the following intermediate phases: Ti 3 P (tetragonal, space group P4 2 /n), Ti 2 P (hexagonal, space group P6/mmm), Ti 1.7 P (orthorhombic, space group P2 1 2 1 2 1 ), Ti 5 P 3 (D8 8 , Mn 5 Si 3 -type hexagonal), Ti 4 P 3 (D7 3 , Th 3 P 4 -type cubic?), TiP (B i , AsTi-type hexagonal), and TiP 2 (orthorhombic, space group Pnma). The Computed Ternary Phase EquilibriaIn their thermodynamic modeling, [2006Oht] used a regular solution model for the liquid, face-centered cubic (fcc), body-centered cubic (bcc), and close-packed hexagonal (cph) phases. The C14 phase (Fe 2 Ti) was described by a three sub-lattice model to account for its wide homogeneity range. The slight solubility of Ti in Fe 3 P and Fe 2 P and the homogeneity ranges of Ti 5 P 3 and TiP were taken into account, by using a two sublattice model. The other binary compounds were modeled as stoichiometric phases. The small homogeneity range of the ternary compound FeTiP (anti PbCl 2 -type orthorhombic) was accounted for, by adopting a three sublattice model. The enthalpies of formation of the binary phosphides and the ternary phosphide FeTiP were evaluated from the electron band energy calculations, using the Full Potential Linearized Augmented Plane Wave (FLAPW) method. See [2006Oht] for details.The experimental phase diagram data of [1959Vog] and[1965Kan] were used in the optimization and the derived interaction parameters were listed. Four vertical sections along the Fe 3 P-FeTiP and Fe-FeTiP joins and at constant 7.5 mass % P and 7.5 mass % Ti respectively, computed by [2006Oht] are compared with the experimental data of [1959Vog] in Fig. 1-4. The agreement is fair. A liquidus Fig. 1 Fe-P-Ti computed vertical section along the Fe 3 P-FeTiP join [2006Oht] Fig. 2 Fe-P-Ti computed vertical section along the Fe-FeTiP join [2006Oht]