Microstructures in a ternary eutectic alloy: devising metrics based on neighbourhood relationships

A Dennstedt,B Nestler,L Ratke,A Choudhury

doi:10.1088/1757-899x/117/1/012025

Abstract

Ternary eutectics, where three phases form simultaneously from the melt, present an opportunity to study the fundamental science of microstructural pattern formation during the process of solidification. In this paper we investigate these phenomena, both experimentally and by phase-field simulations. The aim is to develop necessary characterisation tools which can be applied to both experimentally determined and simulated microstructures for a quantitative comparison between simulations and experiments. In SEM images of experimental cross sections of directionally solidified Ag-Al-Cu ternary eutectic alloy at least six different types of microstructures are observed. Corresponding 3D phase-field simulations for different solidification conditions and compositions allow us to span and isolate the material parameters which influence the formation of three-phase patterns.Both experimental and simulated microstructures were analysed regarding interface lengths, triple points and number of neighbours. As a result of this integrated experimental and computational effort we conclude that neighbourhood relationships as described herein, turn out to be an appropriate basis to characterise order in patterns.

Highlights

During solidification of a eutectic melt several solid phases appear at the same time while no melt will be left
In the present analysis our aim is to investigate the material parameters and conditions which lead to the selection of the different patterns in a ternary eutectic alloy
Therein two intermetallic phases Ag2Al and Al2Cu alternate in a row and one could imagine them as one lamella consisting of two sub-lamellae

Summary

Introduction

During solidification of a eutectic melt several solid phases appear at the same time while no melt will be left. In the case of binary eutectics two phases are created. They can be arranged as lamellae or as fibres in a matrix. Which pattern will be created depends on the eutectic composition. In the case of ternary eutectics three phases are created. Lewis et al published a sketch showing five types of ternary eutectics [1] that were before verbally listed by Ruggiero and Rutter [2]. In reality ternary eutectics are much more complex as shown in this sketch In reality ternary eutectics are much more complex as shown in this sketch ([3, 4, 5, 6, 7] and refs. therein) and their structures generally fail to be describable by the simple geometrical approaches [8]

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