Directional solidification of titanium alloys by electromagnetic confinement in cold crucible

摘要

In order to suppress the reactivity of titanium alloys and modify their structures into directionality, a new solidification method in which its process is continuity of induction melting, electromagnetic confinement and propelling cooling effect is proposed for casting Ti-6Al-4V alloy directionally based on the cold crucible technology. Due to an incomplete contact of the titanium melt with the inner wall of cold crucible with respect to the results of electromagnetic confinement, heat transfer coefficient becomes lower through the melt/crucible interface than that in the conventional casting method. By defining a contact ratio of k_c, the comparison of the heat transfer phenomena in cold crucible with or without electromagnetic effect is taken into account to understand the experimental results to some extent. It is revealed that the solidified front is always convex upward in the periphery areas of the specimens and, in the inner growing zones, the contours of the front will descend from convexity upward to concavity downward with the withdrawal velocities increased. Thus, with slowing down the growth rate, the grain numbers will decrease to a small extent and as shown in this experimental, a single grain has been obtained when the velocity attains 0.5 mm/min. Tensile test shows that directional solidifying ingots have a higher tensile strength and elongation than that without directional structures.