Alloying with Gd and Ag can significantly enhance the comprehensive properties of magnesium alloys, and accurate phase equilibria are a necessity for advanced alloy design. However, literature review reveals limited information on the phase equilibria in the ternary Mg–Gd–Ag system. Thus, in this paper, the phase equilibria of the ternary Mg–Gd–Ag system in the region of 0–50 at.% Gd at 450 °C and 500 °C were investigated by combining the electron probe microanalysis and X-ray diffraction of totally 66 equilibrated alloys, with two isothermal sections at 450 °C and 500 °C established accordingly; and relatively high solid solubility of Ag in GdMg₃ was characterized. Moreover, seven ternary compounds (denoted as τ₁ to τ₇) were found, and their crystal structures were refined by using Rietveld method. The τ₁ was identical to the previously reported X phase with a diamond-cubic structure, while the remaining six ternary compounds (τ₂ to τ₇) were newly found. The seven ternary compounds (τ₁ to τ₇) are among the space groups of Fd$\overline{3}$$\overline{3}$m (τ₁), P4/nmm (τ₂), P6₃mc (τ₃), P6₃mc (τ₄), Pmn2₁ (τ₅), P$\overline{6}$$\overline{6}$2 m (τ₆) and Pc (τ₇). Their homogeneity ranges and lattice parameters were carefully determined. The solubilities of the third elements in the binary compounds of the three subsystems were also well measured. It is anticipated that the presently obtained phase equilibria as well as the crystal structures of ternary compounds in the Mg–Gd–Ag system would serve as a foundation for developing thermodynamic database and alloy design in the near future.

中文翻译：

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在 450 °C 和 500 °C 下，Mg-Gd-Ag 体系中三元化合物的相平衡和晶体结构，成分范围为 0–50 （含 % Gd）


与 Gd 和 Ag 的合金化可以显著提高镁合金的综合性能，精确的相平衡是先进合金设计的必要条件。然而，文献综述揭示了关于三元 Mg-Gd-Ag 系统中相平衡的信息有限。因此，本文通过结合电子探针微量分析和 X 射线衍射技术，研究了三元 Mg-Gd-Ag 体系在 450 °C 和 500 °C 下在 0–50 at.% Gd 范围内的相平衡，并相应地建立了 450 °C 和 500 °C 的两个等温截面;并且表征了 Ag 在 GdMg ₃ 中相对较高的固溶度。此外，发现了 7 种三元化合物 （表示为 τ ₁ 至 τ ₇ ），并使用 Rietveld 方法对其进行了晶体结构的改进。τ ₁ 与先前报道的具有金刚石立方结构的 X 相相同，而其余 6 种三元化合物 （τ ₂ 到 τ ₇ ） 是新发现的。七种三元化合物（τ ₁ 到 τ ₇ ）属于 Fd $\overline{3}$ m （τ ₁ ）、P4/nmm （τ ₂ ）、P6 ₃ mc （τ ₃ ）、P6 ₃ mc （τ ₄ ）、Pmn2 ₁ （τ ₅ ）、P $\overline{6}$ 2 m （τ ₆ ） 和 Pc （τ ₇ ） 的空间群。它们的均匀性范围和晶格参数是经过仔细确定的。第三元素在三个子系统的二元化合物中的溶解度也得到了很好的测量。预计目前获得的相平衡以及 Mg-Gd-Ag 系统中三元化合物的晶体结构将成为在不久的将来开发热力学数据库和合金设计的基础。