Study of the containerless undercooling of Ti-Ce immiscible alloys

Abstract

Ti-Ce immiscible alloys of compositions across the miscibility gap were containerlessly processed in both a low-gravity and a unit-gravity environment. Although undercooling of the single-phase liquid into the miscibility gap could not be observed, undercooling did occur across the miscibility gap for the separated liquid Ti-rich phase. The low gravity, quiescent environment favored higher undercooling over the unit-gravity samples. Every undercooled sample had massive separation of the liquid phases. Metallurgical analysis of samples undercooled in unit-gravity showed signs of vigorous convective stirring and shearing of the L1 Ti-liquid by the applied levitation electromagnetic field. In low-gravity processed samples, the L1 liquid formed a near-concentric sphere within a Ce shell with some residual smaller spherical particles dispersed throughout the Ce. This configuration is predicted from wetting theory and from Marangoni separation. Plots of both the melting and solidification temperatures indicate that the monotectic temperature is 1831 ± 12°K rather than the 1723°K as reported in the literature. From chemical and diffraction analysis, the solubility of Ce in the Ti-rich phase was found to be extended; also, some cerium oxide precipitates formed but no perceptible dissolved oxygen within the Ce or Ti phases was found which indicates that the higher monotectic temperature reported here is probably not an oxygen effect.