Experimental determination of the phase equilibrium in the Mg–Cu–Ca ternary system at 350 °C

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The phase equilibrium of Mg–Cu–Ca ternary system at 350 °C were investigated using thirteen key samples. Scanning electron microscopy (SEM) equipped with energy-dispersive spectroscope (EDS) was employed to investigate equilibrium relationships and phase compositions in alloy samples. Powder X-ray diffraction (XRD) technique was used to analyze the crystal structures of new found phases. Two unreported ternary phases, P1 and Mg25-xCu75Cax were observed and investigated for the first time. The compound P1 has a narrow solid homogeneity ranged from about Mg25Cu35Ca40 to Mg30Cu30Ca40 (in at. %). The solid solubility limit of the compound Mg25-xCu75Cax was found to be 8.03 ≤ xCa ≤ 16.67 with constant value of about 75 at. % Cu at 350 °C. The 2θ of fourteen diffraction peaks of new phase P1 were determined to be 23.0°, 35.9°, 37.3°, 38.9°, 42°, 44°, 47°, 52.5°, 54°, 56.7°, 62.3°, 66.8°, 68.2° and 75.4°. The 2θ of ten diffraction peaks of the new compound Mg25-xCu75Cax were confirmed to be 20.5°, 21.2°, 34.7°, 35.7°, 42.3°, 43.3°, 44.8°, 47.3°, 50.5° and 74.5°. The maximum solid solubility of Ca in the terminal compound MgCu2 was found to be 8.83 at. % at 350 °C. Ternary maximum solid solubility of binary terminal compounds Mg2Ca, Mg2Cu, Cu5Ca and CuCa were less than 2 at. %. In addition, eight three-phase equilibrium relationships were determined in the present work.