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

摘要

Acoustic emission is used here to study melting and solidification ofembedded indium particles in the size range of 0.2 to 3 um in diameter and toshow that dislocation generation occurs in the aluminum matrix to accommodate a2.5% volume change. The volume averaged acoustic energy produced by indiumparticle melting is similar to that reported for bainite formation uponcontinuous cooling. A mechanism of prismatic loop generation is proposed toaccommodate the volume change and an upper limit to the geometrically necessaryincrease in dislocation density is calculated as 4.1 x 10^9 cm^-2 for theAl-17In alloy. Thermomechanical processing is also used to change the size anddistribution of the indium particles within the aluminum matrix. Dislocationgeneration with accompanied acoustic emission occurs when the melting indiumparticles are associated with grain boundaries or upon solidification where thesolid-liquid interfaces act as free surfaces to facilitate dislocationgeneration. Acoustic emission is not observed for indium particles that requiresuper heating and exhibit elevated melting temperatures. The acoustic emissionwork corroborates previously proposed relaxation mechanisms from prior internalfriction studies and that the superheat observed for melting of thesemicron-sized particles is a result of matrix constraint.