Analysis of acoustic emission during the melting of embedded indium particles in an aluminum matrix: a study of plastic strain accommodation during phase transformation

TL;DR

This study uses acoustic emission to analyze melting and solidification of embedded indium particles in aluminum, revealing dislocation generation mechanisms and the effects of particle size, distribution, and superheating on phase transformation.

Contribution

It introduces a novel acoustic emission approach to study phase change mechanisms and dislocation accommodation in aluminum-indium composites.

Findings

Dislocation generation occurs during indium melting to accommodate volume change.

Acoustic energy during melting is comparable to that of bainite formation.

Superheating of particles is linked to matrix constraints and shows no acoustic emission.

Abstract

Acoustic emission is used here to study melting and solidification of embedded indium particles in the size range of 0.2 to 3 um in diameter and to show that dislocation generation occurs in the aluminum matrix to accommodate a 2.5% volume change. The volume averaged acoustic energy produced by indium particle melting is similar to that reported for bainite formation upon continuous cooling. A mechanism of prismatic loop generation is proposed to accommodate the volume change and an upper limit to the geometrically necessary increase in dislocation density is calculated as 4.1 x 10^9 cm^-2 for the Al-17In alloy. Thermomechanical processing is also used to change the size and distribution of the indium particles within the aluminum matrix. Dislocation generation with accompanied acoustic emission occurs when the melting indium particles are associated with grain boundaries or upon solidification where the solid-liquid interfaces act as free surfaces to facilitate dislocation generation. Acoustic emission is not observed for indium particles that require super heating and exhibit elevated melting temperatures. The acoustic emission work corroborates previously proposed relaxation mechanisms from prior internal friction studies and that the superheat observed for melting of these micron-sized particles is a result of matrix constraint.