Formation of High-Angle Grain Boundaries in Iron upon Cold Deformation by Equal-Channel Angular Pressing

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Abstract
At present, the possibility of the formation of high-angle grain boundaries upon severe cold deformation, in particular, equal-channel angular (ECA) pressing is reliably proved. The structure formation upon multi-cycle ECA pressing substantially depends on the route determining the shear plane in the sample upon repeated passes. The route is defined by the rotation of the sample around its axis upon the multi-cycle ECA pressing. There are four main routes: route A, in which the sample is deformed by many passes without any rotations; route Ba, in which the sample is rotated by ± 90°; route Bc, in which the sample is sequentially rotated in the same direction by 90°and route C, in which the sample is rotated by 180° about its axis before each subsequent pass. By the methods of SEM, TEM and EBSD analysis it was shown that the fraction of high-angle boundaries in a-Fe upon cold ECA pressing with an angle of 90° between the channels and N=4 depends on the deformation route and increases according to the route sequence: Ba-C-Bc.