Technical Data

Metallurgical Terms

X-Ray Crystallography.

Max von Laue in 1921 showed that the planes of atoms in crystals act as a diffraction grating to X-rays, which are scattered by them and provide an accurate means of determining the details of the internal atomic structure. X-ray photographs of metals provide information which in many cases cannot be obtained by ordinary microscopic methods. The lines produced by each element, or phase, are characteristic, and their general pattern enables the crystalline structure to be identified. The scale of the pattern can be used to determine accurately the size of the unit cell and, therefore, the distance apart of the individual atoms; and from the relative intensity of the lines can be deduced the distribution throughout the unit cell of the various types of atoms in an alloy, or the degree of preferred orientation in the material. In addition, the sharpness of the lines provides information on both the state of strain and the grain size of the material.