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

摘要

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 Gd_(55-x)Ti_xAl_(25)Cu_(20) the primary solidifying phase changes from Gd_2CuAl (x=0) toward a-Ti (x≥10) with rising Ti-fraction x. This is accompanied by an upturn of the liquidus temperature from T_L = 745 ℃ to T_L>1100℃. The miscibility gap predicted from thermodynamic calculations for Gd_(55-x)Ti_xAl_(25)Cu_(20) 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.