Texture (crystallography)

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Texture pole figures made of gamma-TiAl in an alpha2-gamma two-phase alloy.

In crystallography, texture is understood as the totality of the orientations of the crystallites of a multicrystalline solid .

This results in particular in the anisotropy of the mechanical deformability of many metallic materials , an often cited example of this is the formation of lobes during deep drawing of sheet metal , as well as the anisotropy of the magnetic properties of some soft magnetic (e.g. grain-oriented dynamo sheet ) and hard magnetic materials (e.g. B. anisotropic Alnico , magnets, samarium-cobalt - alloys , anisotropic neodymium-iron-boron alloys, hard magnetic ferrites ).

If the crystallites are distributed completely randomly, the material has isotropic properties, i. H. same properties in all spatial directions. During solidification processes there is often a directed growth of the crystallites, in the borderline case even single crystal formation . Textures are also created by forming a material such as cold rolling or drawing; with hard magnetic materials, powdery crystallites are aligned by magnetic fields during the sintering process. In deep-drawing steels , the cube-shaped crystal lattice is aligned as far as possible so that a spatial diagonal direction of the cube points in the rolling direction. Grain-oriented dynamo sheet has a very sharp texture with a misorientation angle of less than 3 °, the Goss texture {110} <100> named after its discoverer. Here the magnetically easy direction, a cube edge, points in the direction of rolling. A surface diagonal of the cube points in the transverse direction.

history

Although the textural character of many rocks was already known in the 19th century (e.g. slate ), their more detailed analysis was given a decisive boost by the discovery of X-ray diffraction by Laue in 1912. The film process initially allowed the mapping of pole figures from which the preferred orientations (so-called ideal locations ) were estimated. With the development of counter tube detectors and the use of neutron sources in research reactors , the pole figures could be determined much more precisely. Newer methods use 2d detectors, synchrotron radiation , multiple detectors - time-of-flight mass spectrometers and electron diffraction in scanning electron microscopes .

In the 1960s, the quantitative description of the texture using the so-called orientation density distribution function (ODF) was developed.

Web links

literature

  • H.-J. Bunge: Mathematical Methods of Texture Analysis. Akademie-Verlag, 1969.

Individual evidence

  1. ↑ Liss KD, Bartels A, Schreyer A, Clemens H: High energy X-rays: A tool for advanced bulk investigations in materials science and physics . In: Textures Microstruct. . 35, No. 3/4, 2003, pp. 219-52. doi : 10.1080 / 07303300310001634952 .