The mechanism of crystal deformation

Abstract

Microscopy provides an atomistic view of how crystalline materials deform [Also see Report by Kuzmina et al. ] Modern metals and alloys (pure metals containing additives that modify the metal structure and properties) are used in almost all aspects of modern engineering. One of the unique properties of metals and alloys not shared by other materials, such as ceramics, semiconductors, and some polymers, is that they are malleable. That is, they can be plastically deformed to obtain a necessary shape. Furthermore, their degree of ductility can actually be controlled so as to define the level of malleability according to the requirements of the manufacturing process, or what is required during use. The mechanism by which metals deform is via the motion of linear defects at the atomistic scale, called dislocations (see the figure). In metals, dislocations are usually mobile, and their motion provides for the irreversible shifting of atomic planes in a process called slip, resulting in plastic deformation. Without the mechanism of moving dislocations, metals would fail under mechanical loading by brittle fracture, behaving in a manner similar to brittle semiconductors or ceramics. As a result, dislocation theory has been a critical issue from both a fundamental and applied point of view. On page 1080 of this issue, Kuzmina et al. ( 1 ) address perhaps one of the most crucial questions regarding dislocations and their properties: What is the nature of the dislocation core, and can its structure and chemistry be modified to control the properties of dislocations?