| Texture (crystalline) |
Article Index for Texture |
Information AboutTexture (crystalline) |
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One extreme case is a complete lack of texture: a solid with perfectly random crystallite orientation, which will have Isotropic properties (at length scales sufficiently larger than the crystal size). The opposite extreme is a single crystal, which has anisotropic properties by geometric necessity. CHARACTERIZATION AND REPRESENTATION Texture can be determined directly by Laue photography, simple X-ray diffraction, or the EBSD -method (electron backscatter diffraction) in Scanning Electron Microscope s. More recently, Neutron and synchrotron High-energy X-ray diffraction allow to access textures of bulk material and In-situ . Other methods of X-ray Crystallography and of Diffraction in general offer indirect measures of texture. Texture is often represented using a Pole Figure , in which a specified Crystallographic axis (or pole) from each of a representative number of crystallites is plotted in a stereographic projection, along with directions relevant to the material's processing history such as the rolling direction and transverse direction or the fiber axis (see below). The full 3-dimensional representation of crystallographic texture is given by the Orientation Density Function ( ODF ) which can be achieved through evaluation of a complete set of pole figures. Subsequently, all pole figures can be dereived from the ODF. ORIGINS In Wire and Fiber , all crystals tend to have nearly identical orientation in the axial direction, but nearly random radial orientation. The most familiar exceptions to this rule are Fiberglass , which has No crystal structure, and Carbon Fiber , in which the crystalline anisotropy is so great that a good-quality filament will be a distorted single crystal with approximately cylindrical symmetry (often compared to a Jelly Roll ). Single-crystal fibers are also not uncommon. The making of metal Sheet often involves compression in one direction and, in efficient rolling operations, tension in another, which can orient crystallites in both axes. However, Cold Work destroys much of the crystalline order, and the new crystallites that arise with Annealing usually have a different texture. Control of texture is extremely important in the making of Silicon Steel sheet for Transformer cores (to reduce Magnetic Hysteresis ) and of Aluminium Can s (since Deep Drawing requires extreme and relatively uniform Plasticity ). Texture in Ceramic s usually arises because the crystallites in a Slurry have shapes that depend on crystalline orientation, often needle- or plate-shaped. These particles align themselves as water leaves the slurry, or as clay is formed. (unless a Seed Crystal is used) and in the casting of Turbine blades and other Creep -sensitive parts. |
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