Solid/liquid interface evolution including seaweed morphology during directional solidification of Co-Sn alloys

Abstract

The directional solidification of Co–Sn alloys at 300 K/cm was performed systematically with particular attention to the uncommon ‘seaweed’ morphology observed in this system. As withdrawal velocity increased, the quenched solid/liquid interface of Co-20 at.-% Sn hypoeutectic transformed from a planar of α-Co/β-Co3Sn2 lamellar eutectic to dendritic α-Co + eutectic, and the planar interface of Co-24 at.-% Sn eutectic destabilised to cellular. As for Co-30 at.-% Sn hypereutectic, the planar interface transited to dendritic β-Co3Sn2 + eutectic and then to seaweed β-Co3Sn2 + eutectic. The increase of withdrawal velocity results in primary α-Co or β-Co3Sn2 phase growing ahead of the coupled eutectic, and the leading distance is gradually increased with withdrawal velocity. The spacing of the two tips of β-Co3Sn2 seaweed in the alloys followed a power law, [Formula: see text], and the tip splitting frequency versus growth velocity as the function of [Formula: see text].