E. M. Taleff and Pedrazas, N. A., “Perspectives: A New Route for Growing Large Grains in Metals,” Science, vol. 341, pp. 1461–1462, 2013.
(Non-Refereed) Most metallic materials consist of a network of small single crystals, or grains, connected by grain boundaries. This microstructure, which spans length scales from a few nanometers to hundreds of micrometers, controls many of the properties of the metal. Mechanical processing and thermal treatments can be used to alter this microstructure, but the evolution of grains during processing of a material is governed by phenomena that are so complex (relative to our present scientific understanding) that the outcome cannot be reliably predicted. On page 1500 of this issue, Omori et al. (1) describe a wholly unexpected microstructure that arises from synergies among multiple phenomena. They created very large grains in a copper-based shape-memory alloy—a material that will spontaneously recover large strains upon a temperature change—by thermal cycling across temperatures that produce solid-state phase transformations. The subtle mechanisms that apparently act together at elevated temperature to produce this microstructure include internal-stress plasticity (2) and abnormal grain growth (3). This discovery has potential for technological applications that depend on long service lives of shape-memory alloys.