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Section II: Phase Diagram Evaluations

Al-Er-Ti (Aluminum-Erbium-Titanium) V. Raghavan

Recently, [2000Lia] determined an isothermal section for this system at 500 °C.

Binary Systems The Al-Er phase diagram [2002Cac] depicts five intermetallic compounds: ErAl3 (AuCu3-type cubic), ErAl2 (MgCu2-type cubic), ErAl (orthorhombic), Er3Al2 (Zr3Al2type tetragonal), and Er2Al (Co2Si-type orthorhombic). An additional phase Er2Al17 (Th2Zn17-type rhombohedral) was reported by [1993And] and confirmed by [2000Lia]. An updated Al-Ti phase diagram appears in this issue. The Er-Ti phase diagram [Massalski2] contains no intermediate phases. The mutual solid solubility between Er and Ti is limited.

Ternary Compounds Two Al-rich ternary compounds were reported in this system by [1995Nie1,2]. Er6Ti4Al43 (denoted ␶1 here) is Ho6Mo4Al43-type hexagonal, space group P63/mcm, a = 1.1024 nm, and c ⳱ 1.7800 nm [1995Nie1]. The second compound ErTi2Al20 (␶2) is CeCr2Al20-type cubic, space group Fd3 or Fd3m, a ⳱ 1.4662 nm [1995Nie2].

Isothermal Section With starting metals of 99.9% purity, [2000Lia] melted 130 alloy compositions in an arc furnace under Ar atm.

After a final anneal at 500 °C for 4 days, the samples were quenched in an ice-water mixture. The phase equilibria were studied mainly by x-ray powder diffraction. The isothermal section at 500 °C constructed by [2000Lia] is redrawn in Fig. 1 to agree with the accepted binary data. The two ternary compounds Er6Ti4Al43 (␶1) and ErTi2Al20 (␶2) are stable at 500 °C. Er2Al, Er3Al2 and ErAl2 dissolve 2, 3, and 16 at.% Ti, respectively. The solubility of Er in the Ti-Al phases is 0.6 at.% or less. References 1993And: M. Andrecut, I. Pop, and I. Burda, Structural and Magnetic Characteristics of the Intermetallic Compounds Ho2Al17 and Er2Al17, J. Phys. D: Appl. Phys., Vol 26, 1993, p 1810-1813 1995Nie1: S. Niemann and W. Jeitschko, Ternary Aluminides A6T4Al43 (A ⳱ Y, Nd, Sm, Gd-Lu, and U; T ⳱ Ti, V, Nb, and Ta) with Ho6Mo4Al43 Type Structure, J. Solid State Chem., Vol 116, 1995, p 131-135 1995Nie2: S. Niemann and W. Jeitschko, Ternary Aluminides AT2Al20 (A ⳱ Rare-Earth Elements and Uranium; T ⳱ Ti, Nb, Ta, Mo and W) With CeCr2Al20 type Structure, J. Solid State Chem., Vol 114, 1995, p 337-341 2000Lia: J. Liang, J. Huang, H. Zhou, Y. Zhang, and J. Yan, Phase Equilibia of the Al-Ti-Er Ternary System at 500 °C, Z. Metallkde., Vol 91 (No. 8), 2000, p 669-671. 2002Cac: G. Cacciamani, A. Saccone, S. De Negri, and R. Ferro, The Al-Er-Mg Ternary System. Part II: Thermodynamic Modeling, J. Phase Equilibria, Vol 23 (No 1), 2002, p 38-50

Fig. 1 Al-Er-Ti isothermal section at 500 °C [2000Lia]; narrow two-phase regions around tie-triangles are omitted.

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Journal of Phase Equilibria and Diffusion Vol. 26 No. 2 2005