grainorientation

Grain orientation refers to the crystallographic directions of individual grains within a polycrystalline material. Each grain is a single crystal, and its lattice orientation relative to the macroscopic sample axes varies from grain to grain. The collective distribution of orientations is called the material's texture. Orientation can be described quantitatively by Euler angles (for example, phi1, Phi, phi2 in the Bunge convention) or summarized as an orientation distribution function and in pole figures.

Grain orientation is measured with techniques such as electron backscatter diffraction (EBSD) in a scanning electron microscope, X-ray diffraction, and neutron diffraction. These methods yield orientation maps, pole figures, or an orientation distribution function that describe how orientations are distributed. Color-coded EBSD maps are commonly used to visualize texture across a sample.

Textures arise during processing. Plastic deformation by rolling, extrusion, or drawing tends to align lattice directions with the imposed strain, creating a preferred orientation. Subsequent annealing and recrystallization can modify or amplify texture, with the final orientation distribution depending on material system and processing history.

Grain orientation influences anisotropic properties. Mechanical behavior, such as yield strength, ductility, and formability, as well as diffusion, electrical, and magnetic properties, can vary with direction. Grain boundaries with certain misorientation angles can affect recrystallization, grain growth, and crack propagation.

Understanding grain orientation is essential in materials engineering, as controlling texture improves performance in metals, ceramics, and thin films, from structural steels to aluminum alloys and turbine blades.