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Section II: Phase Diagram Evaluations

Al-Fe-Mo (Aluminum-Iron-Molybdenum) V. Raghavan

The early review of this system by [1992Rag] presented two isothermal sections at 1050 and 800
C from the work of [1970Mar]. An update by [2005Rag] reviewed the isothermal section at 1000
C determined by [1999Eum]. Extending this work, [2008Eum1, 2008Eum2] made a detailed investigation of the isothermal sections at 1150, 1000, and 800
C.

Binary Systems The Al-Fe phase diagram [1993Kat] shows a gamma 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 intermediate phases in the system: FeAl2 (triclinic, space group P 1), Fe2Al5 (orthorhombic, space group Cmcm), and Fe4Al13 (or FeAl3; monoclinic, space group C2/m). The Al-Mo phase diagram [2008Eum1] depicts the following intermediate phases: MoAl12

(Al12W-type cubic), MoAl5 (r) (rhombohedral, space group R3c), MoAl5 (h¢) (hexagonal, P321), MoAl5 (h) (hexagonal, P6322), Mo5Al22 (orthorhombic, Fdd2), Mo4Al17 (monoclinic, C2), MoAl4 (monoclinic, Cm), MoAl3 (monoclinic, C2/m), Mo3Al8 (monoclinic, Cm), Al63Mo37, MoAl (bcc), and Mo3Al (A15, Cr3Si-type cubic). In the Fe-Mo phase diagram [Massalski2], the r phase (D8b-type tetragonal) and the R phase (rhombohedral) form through peritectic reactions and decompose above 1200
C. Fe7Mo6 (denoted l; D85-type rhombohedral) and Fe2Mo (C14, MgZn2type hexagonal) form in the solid state. The iron-based bcc phase a and (Mo) show significant mutual solubility.

Ternary Phases Two ternary phases are known in this system: Al8FeMo3 (s1) has the D022, aTiAl3-type of tetragonal structure with lattice parameters of a = 0.3745 nm and c = 0.8390 nm. It forms at a temperature above 1150
C and decomposes eutectoidally at 850
C. It has a small homogeneity range

Fig. 1 Al-Fe-Mo isothermal section at 1150
C [2008Eum2]

372

Journal of Phase Equilibria and Diffusion Vol. 30 No. 4 2009

Phase Diagram Evaluations: Section II

Fig. 2 Al-Fe-Mo isothermal section at 1000
C [2008Eum2, 1999Eum]

Fig. 3 Al-Fe-Mo isothermal section at 800
C [2008Eum1]

Journal of Phase Equilibria and Diffusion Vol. 30 No. 4 2009

373

Section II: Phase Diagram Evaluations of 67.9-69.6 at.% Al and 22.0-24.2 at.% Mo at 1000
C and 67.7-71.6 at.% Al and 22.1-24.4 at.% Mo at 1150
C [2008Eum2]. The other phase s2 also forms above 1150
C, has a homogeneity range and decomposes eutectoidally between 1071 and 1095
C. It has the A2-type bcc structure and a lattice parameter range of 0.296-0.313 nm. On addition of Mo, the high-temperature Fe-Al phase e, which possesses a D82, Cu5Zn8-type cubic structure, undergoes a transition to e* with D810, Cr5Al8-type rhombohedral structure [2008Eum2]. With starting metals of 99.999% Al, 99.95% Fe and 99.95% Mo, [2008Eum1, 2008Eum2] melted 13 binary and 54 ternary alloys by levitation melting under Ar atm. The alloys were annealed at 1150, 1000 and 800
C fo