Phase equilibria and crystal structure of ternary compounds in Al-rich corner of Al-Er-Y system at 673 and 873K

Abstract

Phase equilibria in the Al-rich corner of the Al-Er-Y ternary system from 65 at.% to 100 at.% Al at 673 and 873 K were investigated, and the two isothermal sections were established by X-ray diffraction (XRD), scanning electron microscope (SEM) and electron probe micro analysis (EPMA). Three ternary-phase regions are observed and the phase relations are similar at both isothermal sections. There are two ternary compounds, and a complete crystal structures and composition ranges of the two ternary compounds are determined as τ1 (Al75-76Er15-22Y2-10, R-3m) and τ2 (Al75-76Er11-17Y7-14, P63/mmc) via XRD, focused ion beam coupled with transmission electron microscope (FIB-TEM) and EPMA. Meanwhile, the solubilities of the third element in the binary compounds at both temperatures are measured. The solubility of Er in β-Al3Y phase reaches to 6.6 at.% and that of Y in Al3Er phase reaches to 1.5 at.% after annealing at 873 K. The temperature effect is not obvious for the phase equilibria at 673 and 873 K, but it increases the solubility of Er in β-Al3Y, while it is not obvious for both the solubility of Y in Al3Er and that of Er and Y in (Al). The phase equilibria of the Al-Er-Y ternary system determined by the present work have provided new phase diagram data for a future thermodynamic assessment of this system.