INVESTIGATION OF THE DISLOCATION STRUCTURE PARAMETERS IN SINGLE CRYSTALS BY X-RAY METHOD. Sergey V. Ulshin and Olga P. Karasevskaya. Institute of Metal Physics,Ukrainian Academy of Sciences, 36,Vernadsky pr.,252142 Kiev,Ukraine

The basis for this method is the kinematic theory of X-ray scattering by non-ideal crystal with dislocations. This X-ray method allows to obtain three-dimensional intensity distribution from of I(q) in the cases of homogeneous and nonhomogeneous dislocation structure (DS), pole figure, average meanings of I(q) and their dispersion and to compare theoretical and experimental of I(q) for real crystals and identify DS.

But real crystals very often contain mixture of different DS with numerous parameters, that's why their analyze is complicated.In our paper we modeled several X-ray reflexes and found out that for crystals with different DS reflexes parameters strongly depend on their {hkl} and diffraction vector orientation. Therefore it is necessary to select reciprocal lattice sites, which can allow us to obtain the smallest error for structure parameters. The mathematical criterion for the choosing of the sum of sites which are suitable for investigation have been proposed by us. The investigations of I(q) in the cases of different types DS being in the crystal have shown that I(q) differs essentially for different sites and is very sensitive to types the DS. This makes it possible to develop the express-method for qualitative determination of the DS evolution during the process of single crystals deformation of new kind of the dislocations.

The parameters DS in BCC single crystals were studied. As a result of our experiments the change of the density of screw and edge dislocations {110} ,{112} ,{123} <111> and their distribution during the creep in the temperature interval (0,3-0,6) Tm established. At the high temperature creep multilevel DS is formed. The screw dislocations density really does not increase. At the initial stage of deformation correlation of the edge dislocations density 9:3:1 for the {110} ,{112} ,{123} <111> is formed.Than after 3-6% deformation depending on the single crystals orientation one sign surplus dislocation density essentially increases. At the low temperature creep dislocations density increase linearly with deformation.Correlation of the edge dislocations density 20:2:1 for the {110} ,{112} ,{123} <111> is formed.