The previous review of this system by [1992Rag] presented an isothermal section at 900 °C from the work of [1969Bur]. An update by [2003Rag] reviewed a partial isothermal section at 1150 °C determined by [1999Ste]. The update by [2006Rag] reviewed the more complete study of the system by [2004Ste] and presented a liquidus projection, a reaction scheme and two isothermal sections at 1000 and 800 °C. Very recently, two independent thermodynamic descriptions of this ternary system were reported [2008Guo, 2009Rig].

Binary Systems

The Al-Fe phase diagram [1993Kat] shows that the face-centered cubic (fcc) solid solution based on Fe is restricted by a γ loop. The body-centered cubic (bcc) solid solution α exists in the disordered A2 form as well as the ordered B2 and D03 forms. Apart from the high temperature phase ɛ (D82, Cu5Zn8-type cubic; stable between 1232 and 1102 °C), there are three other intermediate phases: FeAl2(triclinic), Fe2Al5 (orthorhombic), and Fe4Al13 (monoclinic). The Al-Zr phase diagram [Massalski2] depicts the following intermediate phases: ZrAl3 (D023-type tetragonal), ZrAl2 (C14, MgZn2-type hexagonal), Zr2Al3 (orthorhombic), ZrAl (B f , CrB-type orthorhombic), Zr5Al4 (Ga4Ti5-type hexagonal), Zr4Al3 (Ir4Al3-type hexagonal), Zr3Al2 (tetragonal), Zr5Al3 (D8 m , W5Si3-type tetragonal), Zr2Al (B82, Ni2In-type hexagonal), and Zr3Al (L12, AuCu3-type cubic). The Fe-Zr phase diagram [2002Ste] depicts four intermediate phases: Fe2Zr (stable between 1345 and 1240 °C; C36, MgNi2-type hexagonal), Fe2Zr (1673-25 °C; C15, MgCu2-type cubic), FeZr2 (C16, CuAl2-type tetragonal), and FeZr3 (E1 a , Re3B-type orthorhombic).

Ternary Compounds

The ternary phases in this system summarized by [2006Rag] are: (Fe,Al)12Zr (τ1) has the ThMn12-type tetragonal structure. FeAl2Zr6 (τ2) is hexagonal and has a small homogeneity region around the stoichiometric composition. Fe7Al67Zr26 (τ3) has the AuCu3-type cubic structure. In addition to the above, the C14 and C15 Laves phases occur within the ternary region with a range of homogeneity.

Ternary Thermodynamic Descriptions

In their thermodynamic description of this ternary system, [2008Guo] used the substitutional solution model for the liquid, fcc, bcc, and cph phases. The intermetallic phases ZrAl3, Zr2Al3, ZrAl, Zr5Al4, Zr4Al3, Zr3Al2, Zr5Al3, Zr2Al, and Zr3Al with limited Fe solubilities were described with two sublattices, with Al and Fe sharing the first sublattice and Zr in the second sublattice. For FeZr2 and FeZr3, two sublattice models of the type (Al,Fe,Zr)Zr2 and (Al,Fe,Zr)(Fe,Zr)3, respectively, were used. The Laves phases C14 and C15 occur not only as binary members (Al2Zr and Fe2Zr), but also as phases within the ternary region. An expression of the type (Al,Fe,Zr)2(Fe,Zr) was used to describe the Laves phases. The ternary compound τ1 was modeled as (Al,Fe)12Zr. The compound τ2 was modeled as Fe(Al,Zr)2Zr6. The third compound τ3 was taken to be of a fixed composition. The magnetic contribution to the Gibbs energy was taken into account for the fcc, bcc, and cph phases and for the Fe2Zr compound. The binary descriptions of Al-Fe and Al-Zr from the literature were used. The Fe-Zr phase diagram was reassessed by [2008Guo]. Ternary interaction parameters were introduced for the solution phases. The optimized interaction parameters were listed along with those used from literature. The calculated invariant reaction temperatures and compositions were listed and compared with previous work.

In their thermodynamic description, [2009Rig] used the substitutional solution model for the liquid, fcc, bcc, and cph phases. The Fe-based bcc phase was described with a three sublattice model to account for the bcc ↔ B2 ordering transition. The C14 and C15 Laves phases were modeled as different phases, each with two sublattices. In each sublattice, mixing of all elements (Al, Fe, and Zr) takes place, with Al and Fe mainly present in the first sublattice and Zr on the second. As the two-phase fields between C14 and C15 phases are very narrow [2004Ste], the Gibbs energy surfaces separating them were found to be almost identical by [2009Rig]. The binary phases (other than the Laves phases) were treated by [2009Rig] as stoichiometric compounds with no ternary solubility. The τ1 phase was modeled as (Al,Fe)12Zr, whereas the τ2 and τ3 were treated as compounds with fixed composition. A ternary interaction parameter was introduced for the liquid phase. The optimized interaction parameters were listed.

The liquidus lines and primary crystallization fields computed by [2008Guo] and [2009Rig] are shown in Fig. 1 and 2, respectively. The details near the Fe-Al side are omitted. Figure 3 shows a superimposition of the two projections. The sections of [2008Guo], which were drawn on isosceles triangles, are suitably scaled to make the comparison. The two projections are generally similar, but some differences. The regions of primary crystallization of τ2 do not coincide in the two cases. The fields of primary crystallization of the various Laves phases are also somewhat different. In Fig. 2, Zr2Al nucleates in the ternary region, whereas in Fig. 1 it does not take part in the liquid-solid equilibria.

Fig. 1
figure 1

Al-Fe-Zr computed liquidus lines and primary crystallization fields [2008Guo]

Full size image
Fig. 2
figure 2

Al-Fe-Zr computed liquidus lines and primary crystallization fields [2009Rig]

Full size image
Fig. 3
figure 3

Al-Fe-Zr comparison of the computed liquidus lines and primary fields of [2008Guo] and [2009Rig]

Full size image

Figures 4-6 show the computed isothermal section at 1150, 1000, and 800 °C from [2008Guo]. The comparison with the experimental results of [2004Ste] was found to be satisfactory. Figure 7 shows the isothermal section at 900 °C from [2009Rig]. The differences and agreements with the experimental results of [1969Bur] at 900 °C were discussed by [2009Rig].

Fig. 4
figure 4

Al-Fe-Zr computed isothermal section at 1150 °C [2008Guo]

Full size image
Fig. 5
figure 5

Al-Fe-Zr computed isothermal section at 1000 °C [2008Guo]

Full size image
Fig. 6
figure 6

Al-Fe-Zr computed isothermal section at 800 °C [2008Guo]. Narrow two-phase regions are omitted

Full size image
Fig. 7
figure 7

Al-Fe-Zr computed isothermal section at 900 °C [2009Rig]

Full size image

The width of the two-phase regions separating the Laves phases is in the range of ∼1.5-2.5 at.% in the sections computed by [2008Guo], whereas the width is extremely small in the computed sections of [2009Rig]. The width of the two-phase regions between the Laves phases is expected to be not more than 1 at.% [2004Ste], though a precise experimental determination is not available at present. In Fig. 8, the Laves phase regions in the two computed results at 1000 °C are superposed.

Fig. 8
figure 8

Al-Fe-Zr comparison of the Laves phase regions at 1000 °C computed by [2008Guo] and [2009Rig]

Full size image

In conclusion, the differences between the computations of [2008Guo] and [2009Rig] are not much and arise from the different thermodynamic models used and the different emphasis and fit to the experimental data.