Grain boundary

Photomicrograph of a polycrystalline metal; the grain boundaries were made visible by etching.

Illustration of differently oriented grains in a polycrystalline material

A grain boundary is a two-dimensional lattice defect in crystallography . The grain boundary separates areas ( crystallites or grains) in a crystal with different orientations with otherwise the same crystal structure . Grain boundaries can be made visible by chemical etching on the surface.

A distinction is made between small- angle grain boundaries and large-angle grain boundaries.

The large-angle grain boundary is the limit area in which randomly oriented crystal areas collide with one another whose orientation difference exceeds an angle of 15 °. Such a grain boundary no longer only characterizes a fault in one grain , but the grain boundary to the neighboring crystallite. Large angle grain boundaries hinder the movement of dislocations , from one grain to the other. They therefore have a significant influence on the mechanical properties of metallic materials. In most cases the strength is increased by grain boundaries, ie fine-grained materials are stronger. Precipitations, in particular oxides, which preferentially collect or form at grain boundaries, can also have a negative influence on strength.

literature

• Günter Gottstein: Physical basics of materials science . Springer Verlag, Berlin 1998, ISBN 3-540-62670-0 .