Study of the containerless undercooling of Ti-Ce immiscible alloys

Ti-Ce immiscible alloys of compositions across the miscibility gap were con tainerlessly 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 f or the separated liquid Ti-rich phase. The low gravity, quiescent environme nt favored higher undercooling over the unit-gravity samples. Every underco oled sample had massive separation of the liquid phases. Metallurgical anal ysis of samples undercooled in unit-gravity showed signs of vigorous convec tive stirring and shearing of the L-1 Ti-liquid by the applied levitation e lectromagnetic field. In low-gravity processed samples, the L-1 liquid form ed a near-concentric sphere within a Ce shell with some residual smaller sp herical particles dispersed throughout the Ce. This configuration is predic ted from wetting theory and from Marangoni separation. Plots of both the me lting and solidification temperatures indicate that the monotectic temperat ure is 1831 +/- 12 degreesK rather than the 1723 degreesK as reported in th e literature. From chemical and diffraction analysis, the solubility of Ce in the Ti-rich phase was found to be extended; also, some cerium oxide prec ipitates formed but no perceptible dissolved oxygen within the Ce or Ti pha ses was found which indicates that the higher monotectic temperature report ed here is probably not an oxygen effect. (C) 2001 Kluwer Academic Publishe rs.