Melting of embedded anisotropic particles: PbIn inclusions in Al

Abstract

Small particles embedded in the solid state can assume facetted shapes that indicate the anisotropy in interfacial free energy between the particle and the embedding phase. Previous in situ transmission electron microscopy (TEM) of Al–In has shown that such facetted nanoparticles with cubic symmetry embedded in a solid can produce a series of complex melt configurations. To determine the dependence of melt configuration on solid–solid facet energies, this work numerically calculates the equilibrium melt trajectory for a family of cuboctahedral particles parameterized by the ratio of matrix–particle interfacial free energies for orientations taken with respect to the crystal axes of the matrix, ϒ = γ₁₀₀/γ₁₁₁. The calculations assume that equilibrium occurs with the minimization of the total interfacial free energy to determine the stable internal melt configuration for a fixed volume of melt confined within a member of the cuboctahedral family. At particular melt volume fractions, abrupt transitions in shape occur when a stable configuration reaches a touching or necking instability. In situ TEM of a dilute Al alloy containing embedded nanosized PbIn inclusions that gradually melt as the temperature is increased from 230 to 260°C is consistent with the results calculated for ϒ = 1.245.

Keywords:

• PbIn inclusions
• Anisotropic particles
• Embedded anisotropic particles

Acknowledgements

Ellen J. Siem would like to thank Samuel M. Allen and W. Craig Carter for useful discussions. This work was supported by the Danish Natural Sciences Research Council. We are grateful to P. Ochin and his group (CNRS-CECM) for preparing the rapidly solidified materials and to U. Dahmen for access to the microscope (LBNL-NCEM).