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

The phase equilibrium of Mg-Cu-Ca ternary system at 350 degrees 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 <= x(Ca) <= 16.67 with constant value of about 75 at. % Cu at 350 degrees C. The 2q of fourteen diffraction peaks of new phase P1 were determined to be 23.0 degrees, 35.9 degrees, 37.3 degrees, 38.9 degrees, 42 degrees, 44 degrees, 47 degrees, 52.5 degrees, 54 degrees, 56.7 degrees, 62.3 degrees, 66.8 degrees, 68.2 degrees and 75.4 degrees. The 2q of ten diffraction peaks of the new compound Mg25-xCu75Cax were confirmed to be 20.5 degrees, 21.2 degrees, 34.7 degrees, 35.7 degrees, 42.3 degrees, 43.3 degrees, 44.8 degrees, 47.3 degrees, 50.5 degrees and 74.5 degrees. The maximum solid solubility of Ca in the terminal compound MgCu2 was found to be 8.83 at. % at 350 degrees 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. (C) 2019 Elsevier B.V. All rights reserved.