Experimental investigation and thermodynamic calculation of the Mg-Ni-Y system (Y < 50 at.%) at 400 and 500 °C

The phase equilibria of the Mg-Ni-Y ternary system in Y < 50 at.% part have been experimentally investigated and thermodynamically assessed. Fourteen key alloys annealed at 400 and 500 degrees C for 30 days were examined by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and differential scanning calorimeter (DSC). The existence of long-period stacking ordered (LPSO) phases with structures of 18R, 14H and 10H were confirmed and the transformation between those structures were clarified based on the experimental results. The three structures co-existed at 400 degrees C, but 10H may transform to 18R through a solid-state reaction 10H + Mg2Ni -> 18R + MgNi4Y at 450.5 degrees C. The MgNi4Y phase exhibited a solid solution range with about Mg1-xYxNi2 (0.42 < x < 0.50). A self-consistent thermodynamic description of the MgeNieY ternary system was optimized through considering the experimental results. (C) 2015 Elsevier B.V. All rights reserved.