Experimental determination of the phase equilibria of the Mg-Nd-Zn system at 320 °C

The phase equilibria of the Mg-Nd-Zn system at 320 degrees C were investigated with an Mg-Nd-Zn diffusion couple and 34 equilibrated alloys, by means of X-ray diffraction technique and electron probe microanalyses. Eight ternary phases, denoted as tau-tau(7) and T-NdMg12, respectively, were found at 320 degrees C. It was revealed that the T-NdMg12 phase is based on the metastable NdMg12 compound and stabilized by the substitution of Zn for Mg. The tau(1) phase with a C-centered orthorhombic crystal structure was determined to have a composition range of 7.4-7.7 at.% Nd and 25.8-40.1 at.% Zn. The tau(2) phase with a hexagonal crystal structure was measured to have a composition range of 6.3-7.8 at.% Nd and 61.0-64.0 at.% Zn. The crystal structures of the five ternary phases tau(3)-tau(7) are still unknown. Four ternary phases, viz. T-NdMg12 and tau(5) to tau(7), can be regarded as the newly found ternary phases in the present work. According to the present work, the tau(3), tau(4) and tau(5) phases have the Zn composition ranges of 61.6-64.6 at.% Zn, 54.4-67.9 at.% Zn and 59.5-64.5 at.% Zn, and have the approximate Nd contents of 10.4, 13.5 and 17.2 at.% Nd, respectively. The tau(6) phase has a approximate chemical composition of Nd15.7Mg8.4Zn75.9 while the tau(7) phase has a composition range of 58.0-60.2 at.% Zn at about 21.3 at.% Nd. (C) 2014 Elsevier B. V. All rights reserved.