X-RAY DETERMINATION OF DISLOCATION DENSITIES IN PLASTICALLY DEFORMED Cu SINGLE AND POLYCRYSTALS

D. Breuer, P. Klimanek

Freiberg University of Mining and Technology, Institute of Physical Metallurgy D - 09 596 Freiberg, Germany

The analysis of broadened X-ray diffraction peaks is a suitable procedure for the integrated investigation of dislocation arrangements in plastically deformed crystalline materials [1,2,3]. However, especially in polycrystalline materials the evaluation of the line broadening is complicated by

  1. occurrence of instrumental line broadening due to the non-ideal conditions of the diffraction experiment and
  2. structural inhomogeneity (i.e. significant changes of the local dislocation arrangement in single crystals or variations of the defect content of the grains in polycrystals).
Instrumental line broadening can be minimized by application of high-resolution X- ray diffractometry or has approximately to be eliminated by means of a standard (Stokes - correction; [4]), for instance) the influence of structural inhomogeneity may be taken into account by averaging over a sufficiently large sample volume or, e.g. in coarse-grained polycrystals, by investigation of single-grain scattering. In order to check the reliability and the comparability of dislocation densities obtained with different diffraction methods, [001]-oriented Cu single crystals and polycrystalline Cu with grain sizes of 100 m and 40 m were plastically deformed in compression and investigated by means of

- a double-crystal spectrometer (DCS) with a nearly-perfect Ge monochromator and

- a conventional Bragg-Brentano powder diffractometer (XPD) with a secondary beam graphite monochromator.

In the DCS experiments the instrumental line broadening could be neglected (cp. [5]), in the XPD investigations it was determined by a Cu standard. For the estimation of the dislocation densities the theory of Krivoglaz et.al [3] for dislocation arrangements with weak defect correlation was used. In the polycrystalline materials a good agreement was found between the results of DCS and XPD. Moreover, the dislocation densities of the single crystals can well be related to those of the polycrystals via the flow stress.

1. Krivoglaz, M.A., Ryaboshapka, K.P.: Fiz. Met. Metalloved. 15 (1963) 18
2. Wilkens, M. : phys.stat.sol. (a) 2 (1970) 359
3. Krivoglaz, M.A., Martynenko, O.V., Ryaboshapka, K.P. : Fiz. Met. Metalloved. 55 (1983) 5
4. Stokes, A.R.: Proc. Phys. Society (London) 61 (1948) 382
5. May, Ch., Klimanek, P.: Z. Kristallographie, in preparation