Materials Research Lecture

The size distribution of particles, which is essential for many properties of nanomaterials, is equally important for the mechanical behavior of the class of alloys whose strength derives from a dispersion of nanoscale precipitates. However, particle size distributions formed by solid-state precipitation are generally not well controlled. This talk will describe, through the example of core shell precipitates in Al Sc Li alloys, an approach to forming highly monodisperse particle size distributions by simple solid-state reactions. The approach involves the use of a two-step heat treatment, whereby the core formed at high temperature provides a template for growth of the shell at lower temperature. If the core is allowed to grow to a sufficient size, the shell develops in a size focusing regime, where smaller particles grow faster than larger ones.

The experimental observations underlying this discovery exploit state of the art characterization based on advanced electron microscopy techniques, and is complimented by theoretical modeling combining mean-field kinetic theories with first-principles modeling. These results suggest strategies for manipulating precipitate size distributions in similar systems through simple variations in thermal treatments.