FORMATION OF INTERNAL STRUCTURE IN THE DEFORMATION ZONE DURING ROLLING OF THE BCC SINGLE CRYSTAL (110)[001]

Structure formation staging of a single crystal (110) [001] of the alloy with Fe-3 % Si bcc was investigated directly in deformation zone during cold rolling. Laboratory rolling mill was abruptly stopped during the rolling of every sample to create a visible «deformation zone». Lubrication was used on some samples to reduce the friction coefficient. Deformation structure was investigated by the methods of metallography and orientation electron microscopy. The connection of the experimental data with the calculated stress state was analyzed in Deform-3D program for different values of cold rolling friction coefficient. It was demonstrated that stress state in relation to friction coefficient can considerably influence the generation of mesostructure and crystal texture evolution in the material. It was observed that deformation bands formed in a cold rolled single crystal that was subject to high friction and relatively low strain value. Orientation analysis of the deformation bands linkage demonstrated in this area the existence of alternating microbands with slightly different orientations, separated from each other by low-angle boundaries. In case of single crystal (110)[001] rolling with lubrication (low friction) twinning was noted even for low strain level. As it seems, the reduction of surface energy input into the total energy of twin formation was the result of twinning. It was demonstrated that during all deformation process twins of both systems either preserved a strong L3 crystallographic connection with the matrix or L3 disorientation transformed into close special disorientations Y.llb and L43c in connection to local reorientation of crystal lattice. Based on experimental data dislocation model of deformation mesostructure formation during single crystal (110)[001] cold rolling has been proposed. This model deals with microbands formation at the initial stage of deformation bands appearance, the formation of transition bands parallel to rolling plane which retain initial orientations in dynamics, formation of transition bands tilted to the rolling plane with the habit planes parallel to {112} matrix planes. These transition bands are equivalent to shear bands the habit of which makes the angle of about 17° with the rolling plane.

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