Doublon Growth in Solidification

TL;DR

This paper investigates the formation and characteristics of doublon growth structures during directional solidification of succinonitrile with various solutes, revealing their dependence on solute concentration and sample orientation.

Contribution

It provides experimental insights into doublon morphology, showing how solute concentration and orientation influence doublon selection and stability in diffusion-limited growth.

Findings

Doublons are favored at low solute concentrations.

Doublons exhibit preferred growth directions.

Transitions occur between seaweed and doublon growth modes.

Abstract

We present experiments on the doublon growth morphology in directional solidification. Samples used are succinonitrile with small amounts of poly(ethylene oxide), acetone, or camphor as the solute. Doublons, or symmetry-broken dendrites, are generic diffusion-limited growth structures expected at large undercooling and low anisotropy. Low anisotropy growth is achieved by selecting a grain near the $\{111\}$ plane leading to either seaweed (dense branching morphology) or doublon growth depending on experimental parameters. We find selection of doublons to be strongly dependent on solute concentration and sample orientation. Doublons are selected at low concentrations (low solutal undercooling) in contrast to the prediction of doublons at large thermal undercooling in pure materials. Doublons also exhibit preferred growth directions and changing the orientation of a specific doublonic grain changes the character and stability of the doublons. We observe transitions between seaweed and doublon growth with changes in concentration and sample orientation.