Formation of Rhombohedrons in the Copper Structure after Drawing and Equal Channel Angular Pressing

In this work, the methods of scanning electron microscopy and transmission electron microscopy to study the deformation refinement of copper grains from 200 μm to 50 nm in a 20 mm workpiece’s cross section were used. A grain refinement pattern during the transition of the copper structure from mesolevel (d ≥ 250 nm) to the microlevel (d < 250 nm) after drawing and two, six, and eight passes of the ECAP along the Вс route at room temperature was proposed. It was shown that when shear bands intersect at an angle of 45°, grains in the form of rhombuses or hexagons with a width of 500–800 nm are separated by subgrains with a width of 150–250 nm with their own structure of nano bands with a width of 50 nm, and submicrograins of 50–100 nm. After 8 passes ECAP, high-angle grain boundaries of hexagons were formed at the location of triple grain junctions as a result of primary recrystallization. The scheme of deformation grain refinement was changed as follows. After two ECAP passes, microbands with a cellular structure 100–200 nm wide with an apex angle of 45° were formed. This herringbone-like shear bands were formed. After six ECAP passes, a banded and “lattice” structure was formed at the places of multiple intersections of shear bands, with rhombohedrons forming in the center. After eight ECAP passes, the resulting grain refinement pattern consisted of fragmented shear bands of 400–500 nm wide and shear bands of 300 nm wide located at an angle of 45°.