Hexagonal eutectic solidification patterns operating near a marginal stability point

TL;DR

This study investigates the long-term behavior of hexagonal eutectic solidification patterns near a marginal stability point, revealing how minor imperfections influence pattern dynamics and spacing selection.

Contribution

It demonstrates that slight curvature-induced dilatation drives patterns near a stability threshold, clarifying the mechanism behind spacing selection in bulk eutectic growth.

Findings

Patterns are driven into a near-marginal stability regime by minor isotherm curvature.

The system's dynamics are influenced by a slow pattern dilatation.

Instrumental imperfections can maintain the system near a stability threshold.

Abstract

We study the long-time dynamics of hexagonal directional-solidification patterns in bulk samples of a transparent eutectic alloy using an optical method which permits real-time observation of the growth front. A slow dilatation of the patterns due to a slight curvature of the isotherms drives the system into a permanent regime, close to the threshold for the rod splitting instability. Thus an apparently minor instrumental imperfection suffices to maintain the system near a marginal stability point. This answers the long-standing question of spacing selection in bulk eutectic growth.