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Section II: Phase Diagram Evaluations

Al-Gd-Ti (Aluminum-Gadolinium-Titanium) V. Raghavan

Recently, [2002Zho] determined an isothermal section for this system at 500 °C, which depicts two ternary compounds.

type hexagonal, space group P63/mcm, a = 1.1072 nm, and c ⳱ 1.7942 nm [1995Nie1]. The second compound GdTi2Al20 (␶2) is CeCr2Al20-type cubic, space group Fd3 or Fd3m, a ⳱ 1.4684 nm [1995Nie2].

Binary Systems

Ternary Isothermal Section

The Al-Gd system [2000Sac] has five intermediate compounds of fixed stoichiometry: GdAl3 (D019-type hexagonal), GdAl2 (C15-type cubic), GdAl (ErAl-type orthorhombic), Gd3Al2 (Zr3Al2-type tetragonal), and Gd2Al (Co2Si-type orthorhombic). An update of the Al-Ti phase diagram appears in this issue. There are no intermediate phases in the Gd-Ti system [Massalski2].

With starting materials of 99.9% purity, [2002Zho] melted 206 alloy samples in an arc furnace under Ar atm. The alloys were given a final anneal at 500 °C for 7 days and quenched in an ice-water mixture. The phase equilibria were studied by optical and scanning electron metallography, x-ray powder diffraction and electron probe microanalysis. The isothermal section constructed by [2002Zho] is redrawn in Fig. 1 to agree with the accepted binary data. The two ternary compounds found by [1995Nie1,2] are present at 500 °C [2002Zho]. The maximum solubilities of Ti in the binary compounds Gd2Al, Gd3Al2, and GdAl2 are 2.0, 3.5, and 16.3 at.%, respectively, with Ti substituting for Al. The solubility of the third component in the other binary phases is not significant.

Ternary Compounds Two ternary compounds were reported in this system by [1995Nie1,2]. Gd6Ti4Al43 (denoted ␶1 here) is Ho6Mo4Al43-

Fig. 1 Al-Gd-Ti isothermal section at 500 °C [2002Zho]; narrow two-phase regions around tie-triangles are omitted.

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

Phase Diagram Evaluations: Section II References 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 2000Sac: A. Saccone, A.M. Cardinale, S. Delfino, and R. Ferro, Gd-Al and Dy-Al Systems: Phase Equilibria in the 0 to 66.7 at.% Al Composition Range, Z. Metallkde., Vol 91 (No. 1), 2000, p 17-23 2002Zho: H. Zhou, Y. Zhan, J. Yan, and S. Yuan, Phase Relationships in the Gd-Ti-Al Ternary System at 500 °C, J. Mater. Sci., Vol 37, 2002, p 1203-1205

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

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