Phase equilibria of the Mg–Sn-Nd ternary system at 400 °C

Abstract

The phase equilibria of the Mg–Sn-Nd ternary at 400 °C were investigated by X-ray powder diffraction (XRD), scanning electron microscope equipped with an energy dispersive spectrometer (SEM-EDS). Seven stable ternary compounds and one eutectoid decomposed structure (A1) were observed in the section. The crystal structure for the phases: τ1 (MgSnNd, I4/mmm, tI12) and τ2 (MgSn2Nd, I42 m, tI32) were confirmed. τ3 (Mg75Sn3.5Nd21.5) is the iso-structure of Mg23SnLa6 (Zn23SiZr6 prototype, cF120 Pearson's code) and τ4 (Mg40+3Sn26.7-3Nd33.3) has the same structure and homogeneity range of Mg4-xSn2+xLa3(0.12 < x ≤ 0.4) (Cu4Si2Zr3 prototype, hP9 Pearson's code). The crystal structure of τ5 (Mg44Sn34Nd22), τ6 (Mg40Sn36Nd24) and τ7 (Mg16+3Sn45Nd39-3) are not determined. Two binary compounds Nd3Sn and Nd2Sn3, which were not included in the Nd–Sn binary phase diagram, were detected in this work. All detected Nd–Sn binary compounds show different amounts of Mg solubility, among which NdSn3 and Nd5Sn4 dissolve up to 10 and 6.8 at.% Mg and the rest Nd–Sn binary phases contain 1–3 at.% Mg. The MgNd phase dissolves up to 6.0 at. % Sn.