Phase relationships in the neodymium-magnesium alloy system

Description

The Nd-Mg system was studied using differential thermal analysis (DTA), X-ray examination, metallography, and microprobe analysis. The following intermetallic compounds were found to exist and their crystal structures confirmed or determined: NdMg (cubic, cP2 CsCl type, melting point 800 °C), NdMg2 (cubic, cF24 MgCu2 type, peritectic formation ∼755 °C), NdMg3 (cubic, cF16 BiF3 type, melting point 780 °C), and Nd5Mg41 (tetragonal, tI92 Ce5Mg41 type, decomposes peritectically at 560 °C). The NdMg2 phase undergoes a eutectoidal decomposition at 660 °C. Three eutectic equilibria were observed to occur at 42.5 at. pct Mg and 775 °C, 64.5 at. pct Mg and 750 °C, and 92.5 at. pct Mg and 545 °C, respectively. In the Nd-rich alloys, previously determined data[15] concerning the Mg solubility in α-Nd (8.2 at. pct Mg, ≈550 °C) were accepted. The Mg solubility in β-Nd was evaluated as 34 at. pct Mg at 775 °C. The β-Nd phase was observed to decompose eutectoidally at 17 at. pct Mg and 545 °C. Moreover, in the Mgrich alloys, a metastable NdMg12 phase (tetragonal, tI26 ThMn12 type) was observed in samples quenched from the liquid. The general properties of the Nd-Mg phases are compared with those of the R-Mg compounds and briefly discussed. © 1990 The Metallurgical of Society of AIME.

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