ADVANCED NEUTRON DIFFRACTION FOR MICROSTRUCTURE ANALYSIS OF POLYCRYSTALLINE MATERIALS. P.Mikula, P.Lukas, M.Vrana, P.Strunz and V.Wagner* Nuclear Physics Institute, 25068 Rez near Prague, Czech Republic, *Physikalisch Technische Bundesanstalt, 38116 Braunschweig, Germany
Recently, we have developed novel high-resolution modifications of conventional neutron diffraction techniques - Bragg diffraction peak analysis (BDPA) and Energy Dispersive Transmission Analysis (EDTA) - for the strain and microstructure distortions of polycrystalline materials. Using Bragg diffraction optics (focusing in real and momentum space) the new modifications provide good diffractometer luminosity and [[Delta]]d/d resolution of about 10-3 of the diffraction profile of an etalon sample. The resolution is represented by the FWHM and in the latter case of EDTA it is related to the Gaussian of the corresponding cumulative function. [1-3]. Besides the measurements of macrostrains with an extremely high sensitivity up to 10-5 the novel modifications provide also unique possibilities for microstrain, grain size and dislocation density studies of plastically deformed polycrystalline materials on the basis of the diffraction profile analysis. In contrast to X-ray profile analysis, the experiments with neutrons are not restricted to the surface, but can be performed on rather large bulk samples and at much higher scattering angles where the X-ray intensities strongly decrease. These modifications have been implemented on diffractometers in NPI and PTB where effects of both elastic and plastic deformations are commonly investigated, and which can be used by external users. Thanks to the exploitation of focusing effects and special diffraction geometries in combination with position sensitive detectors for data acquisition, reasonable counting times even at our medium power reactors are achieved. Results of investigations obtained with different plastically deformed polycrystalline samples of Fe(110) and Fe(321) will be presented.
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[2] M.Vrana et al., Nucl. Instrum. Methods, A338 (1994) 125.
[3] P.Mikula et al., Physica B, 213&214 (1995) 845.