Grain boundaries

Article By:

Sass, Stephen L. Department of Materials Science and Engineering, Cornell University, Ithaca, New York.

Last reviewed:January 2020

DOI:https://doi.org/10.1036/1097-8542.296700

The internal interfaces that separate neighboring misoriented single crystals in a polycrystalline solid. Most solids such as metals, ceramics, and semiconductors have a crystalline structure, which means that they are made of atoms which are arranged in a three-dimensional periodic manner within the constituent crystals. Most engineering materials are polycrystalline in nature in that they are made of many small single crystals which are misoriented with respect to each other and meet at internal interfaces which are called grain boundaries. These interfaces, which are frequently planar, have a two-dimensionally periodic atomic structure. A polycrystalline cube 1 cm on edge, with grains 0.0001 cm in diameter, would contain 10¹² crystals with a grain boundary area of several square meters. Thus, grain boundaries play an important role in controlling the electrical and mechanical properties of the polycrystalline solid. It is believed that the properties are influenced by the detailed atomic structure of the grain boundaries, as well as by the defects that are present, such as dislocations and ledges. Grain boundaries generally have very different atomic configurations and local atomic densities than those of the perfect crystal, and so they act as sinks for impurity atoms which tend to segregate to interfaces. See also: Crystal defects; Crystal structure

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