Stability of three-phase ternary-eutectic growth patterns in thin sample

Near-eutectic ternary alloys subjected to thin-sample directional solidification can exhibit stationary periodic growth patterns with an ABAC repeat unit, where A, B, and C are the three solid phases in equilibrium with the liquid at the eutectic point. We present an in-situ experimental study of the dynamical features of such patterns in a near-eutectic In-In2Bi-Sn alloy. We demonstrate that ABAC patterns have a wide stability range of spacing lambda at given growth rate. We study quantitatively the lambda-diffusion process that is responsible for the spacing uniformity of steady-state patterns inside the stability interval. The instability processes that determine the limits of this interval are examined. Qualitatively, we show that ternary-eutectic ABAC patterns essentially have the same dynamical features as two-phase binary-eutectic patterns. However, lamella elimination (low-lambda stability limit) occurs before any Eckhaus instability manifests itself. We also report observations of stationary patterns with an [AB](m)[AC](n) superstructure, where m and n are integers larger than unity. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.