The impact of particle morphology on the melting characteristics of matrix-embedded Pb nanocrystals

Abstract

The melting behaviour of Pb nanoparticles embedded in an Al matrix (0.5 at. % Pb) synthesized by high-energy ball milling is investigated. By differential scanning calorimetry it is shown that, as the material is cycled repeatedly through the melting transition, the particles melt reversibly at temperatures T f below the melting temperature T f 0 - of bulk Pb. However, after a suitable heat treatment the nanoparticle morphology is modified such that a significant fraction of the Pb particles now melts at increased temperatures Tf > T 0 f. Transmission electron microscopy gives strong indications as to the origin of the change in melting behaviour; strains in the as-prepared material do not recover during cycling through Tf, and resolidification of the molten particles in the strained matrix brings the particles back to the initial structure with curved interfaces and small, but noticeable, misalignments relative to the cube-on-cube orientation relationship. Annealing leads to strain relief and to faceted Pb particles. The relation between strains and particle morphology is discussed.