Al-Cu-Gd (Aluminum-Copper-Gadolinium)

Studies of this system by [1988Pre] gave an isothermal section at 497 °C (770 K), depicting several ternary compounds. [2001Gum] identified new ternary compounds and refined the structure of the previously known compounds. They constructed an isothermal section at 597 °C (870 K), depicting seven ternary compounds and significant solubility of the third component in several binary compounds. This system is included in the review of Al-Cu-RE systems by [2004Ria].

Binary Systems

The Al-Cu phase diagram [1998Liu] depicts a number of intermediate phases: CuAl₂ (C16-type tetragonal, denoted θ), CuAl (η₁, orthorhombic), CuAl (η₂, monoclinic), Cu₅Al₄(LT) (ζ, orthorhombic), ɛ₂ (B8₂, Ni₂In-type hexagonal), ɛ₁ (bcc), Cu₃Al₂ (δ, rhombohedral), Cu₉Al₄(HT) (γ₀, D8₂, Cu₅Zn₈-type cubic), Cu₉Al₄(LT) (γ₁, D8₃-type cubic), and Cu₃Al (β, bcc). In the above, HT = high-temperature and LT = low-temperature. The Al-Gd system [Massalski2] has the following intermediate phases GdAl₃ (D0₁₉, Ni₃Sn-type hexagonal), GdAl₂ (C15, MgCu₂-type cubic), GdAl (ErAl-type orthorhombic), Gd₃Al₂ (Zr₃Al₂-type tetragonal), and Gd₂Al (C23, Co₂Si-type orthorhombic). The Cu-Gd phase diagram [Massalski2, 2004Ria] depicts the following intermediate phases: GdCu₆, βGdCu₅ (D2 _d , CaCu₅-type hexagonal), αGdCu₅ (AuBe₅-type cubic), Gd₂Cu₉ (monoclinic), GdCu₂ (CeCu₂-type orthorhombic), and GdCu (B2, CsCl-type cubic).

Ternary Phases

[2001Gum] identified four new ternary compounds in this system and refined the crystal structures of two previously known compounds. The structural details of seven compounds, numbered 1 to 7 by [2001Gum] (denoted τ₁ to τ₇ here) are given in Table 1.

Table 1 Al-Cu-Gd crystal structure and lattice parameter data [2001Gum]

Isothermal Section

With starting metals of 99.95 mass % Al, 99.95 mass % Cu, and 99.5 mass % Gd, [2001Gum] prepared 38 ternary alloys by arc-melting under Ar atm. The alloys were annealed at 597 or at 497 °C for 1000 h and quenched in water. The phase analysis was carried out with x-ray powder diffraction. The same seven ternary compounds were found at both temperatures. The ternary compound GdCuAl₃ reported by [1988Pre] with the Al₄Ba-type tetragonal structure was not found by [2001Gum] at 597 or 497 °C. The isothermal section at 597 °C (870 K) constructed by [2001Gum] for Gd content up to 33.3 at. % is shown in Fig. 1. Along the Al-Cu side, at this temperature, the liquid phase (L) is present instead of θ. The ternary compounds are shown at the compositions listed by [2001Gum]. The binary compound GdCu₅ and GdCu₂ dissolve up to 50 and 4 at. % Al, respectively. GdAl₂ dissolves up to 5 at. % Cu.

Fig. 1

Al-Cu-Gd isothermal section at 597 °C (870 K) [2001Gum]