The Gd-Al-Si Isothermal Section at 500 °C

Phase relations in the Gd-Al-Si system have been established and experimentally studied at 500 degrees C. The system has been experimentally investigated by mean of scanning electron microscopy (SEM), electron microprobe analysis (EDXS) and x-ray powder diffraction (XRPD). The existence of four ternary compounds has been confirmed: tau(1) GdAl2Si2 (hP5-CaAl2Si2 type), tau(2) GdAlSi (tI12-alpha ThSi2 type), tau(3) Gd4AlSi3 (oC8-CrB type) and tau(4) Gd6Al3Si (tI80-Tb6Al3Si type). Three ternary compounds show a composition homogeneity range: tau(2) dissolves Si up to about 37 at.%, tau(3) shows an homogeneity range (towards the GdSi compound) to 45 at.% Si concentration value, finally the tau(4) phase dissolves 5 at.% of Si. All binary compounds dissolve the third element, except for GdAl The ternary system is characterized by 16 three-phase fields, and 16 two-phase fields.