Liquid phase separation, solidification and phase transformations of Gd-Ti and Gd-Ti-Al-Cu alloys

Phase equilibria of the quaternary Gd-Ti-Al-Cu system have been studied with particular respect to solidification and phase separation phenomena in metallic glasses. Along the section Gd55−xTixAl25Cu20 the primary solidifying phase changes from Gd2CuAl (x=0) toward α-Ti (x≥10) with rising Ti-fraction x. This is accompanied by an upturn of the liquidus temperature from TL=745 °C to TL>1100 °C. The miscibility gap predicted from thermodynamic calculations for Gd55−xTixAl25Cu20 melts at intermediate Ti-fractions was not verified experimentally. Unlike binary Gd-Ti melts, levitated Gd-Ti-Al-Cu droplets do not exhibit liquid phase separation features after quenching from different holding temperatures, even at high melt undercooling up to 200 K prior to solidification.