INFLUENCE OF PLASTIC DEFORMATION ON POINT DEFECT STRUCTURE OF NiAl COMPOUND STUDIED WITH LAUE METHOD. Hui Zhang, Hartmut Werker, Gernot Zahn and Peter Paufler, Institut fr Kristallographie und Festkrperphysik, TU-Dresden, 01062 Dresden, Germany

To study the influence of plastic deformation on the structure of point defect in the intermetallic compound NiAl, the advantage of Laue method, its full spectral exposure, and advantages of the image plate, its high sensitivity, wide dynamic range and high counting rate, are combined. Furthermore, back reflection exposure is chosen to avoid sample modification, so that the real deformation effect can be observed.

Laue method is a laboratory routine to determine crystal orientation and to study disorders, such as grain structure and mosaic spread. However, it is not so straight forward to get structure factor with Laue method. The measured intensity must be normalized with some extra factors, such as spectral intensity of incident radiation, spectral sensitivity of the detector, and readout efficiency, besides well known factors, such as polarization factor, Lorentz factor, temperature factor and absorption factor. The solution is further hindered by the so called multireflection problem. Since many of, if not most of, strong low index reflections are involved in multiplicity, it is necessary to deconvolute energy overlap. It is achieved experimentally either by rotating sample or by changing tube voltage.

For samples like NiAl which acquire high symmetry, it is possible to get a quite complete intensity data set on a single exposure. Fourier synthesis is then carried out with structure factors thus extracted and electron distribution map is plotted to show some features of point defect configuration. Even if the data set is not so complete, by comparing measured structure factors with that calculated based on theoretical models, it is still possible to determine point defect structure.