The Growth Pattern of Co3Sn2 in Directional Solidification of Co-Sn Hypereutectic Alloy Melts

Abstract

Co70Sn30 hypereutectic alloy was directionally solidified at various velocities at temperature gradients of 200 and 300 K/cm. At a given temperature gradient, α-Co/β-Co3Sn2 lamellar eutectic grows with a planar interface when the withdrawal velocity is small. The increases of withdrawal velocity result in primary β-Co3Sn2 phase growing ahead of the eutectic, and its morphology changes from dendritic pattern to fractal seaweed pattern above a critical withdrawal velocity. The rise of the temperature gradient narrows the withdrawal velocity range within which primary β-Co3Sn2 phase can grow in the dendritic pattern. The tip-splitting frequency of the β-Co3Sn2 seaweed vs growth velocity shows a power law $$ f \propto V^{{{3 \mathord{\left/ {\vphantom {3 2}} \right. \kern-0pt} 2}}} $$ The change of the primary arm spacing of β-Co3Sn2 with the growth velocity follows $$ d_{1} = k_{1} V^{{ - e_{1} }} , $$ where the exponent e1 is larger for seaweed growth than for dendritic growth.