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hase Diagram Evaluations: Section II

Al-Fe-Zr (Aluminum-Iron-Zirconium) V. Raghavan

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 c loop. The body-centered cubic (bcc) solid solution a exists in the disordered A2 form as well as the ordered B2 and D03 forms. Apart from the high temperature phase e (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 (Bf, CrB-type orthorhombic), Zr5Al4 (Ga4Ti5-type hexagonal), Zr4Al3 (Ir4Al3-type hexagonal), Zr3Al2 (tetragonal), Zr5Al3 (D8m, W5Si3-type tetragonal), Zr2Al (B82, Ni2In-type hexagonal), and Zr3Al (L12, AuCu3type cubic). The Fe-Zr phase diagram [2002Ste] depicts four intermediate phases: Fe2Zr (stable between 1345 and 1240 °C; C36, MgNi2-type hexagonal), Fe2Zr (167325 °C; C15, MgCu2-type cubic), FeZr2 (C16, CuAl2-type tetragonal), and FeZr3 (E1a, Re3B-type orthorhombic).

Ternary Compounds The ternary phases in this system summarized by [2006Rag] are: (Fe,Al)12Zr (s1) has the ThMn12-type tetragonal structure. FeAl2Zr6 (s2) is hexagonal and has a small homogeneity region around the stoichiometric composition. Fe7Al67Zr26 (s3) 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 s1 was modeled as (Al,Fe)12Zr. The compound s2 was modeled as Fe(Al,Zr)2Zr6. The third compound s3 was taken to be of a fixed composition. The magnetic contributi