Effect of temperature of HPT deformation and the initial orientation on the structural evolution in single-crystal niobium

Behavior of Nb and Cu–Nb Composites under Severe Plastic Deformation and Annealing

“…46,47) As mentioned above, the strain under the high-pressure torsion is non-uniformly distributed along the specimen radius, growing from the center to periphery, and hence the structure also refines non-uniformly and microhardness differs along the radius as well. 17,49,69,70) On the other hand, many experimental data, including ours, indicate, that this non-uniformity of structure and properties, particularly, microhardness, level off with the strain increasing. 18,22,47) It is illustrated by Fig.…”

“…As well documented in the literature [see, e.g., Refs. 49,62)], the submicrocrystalline structure formation under the HPT proceeds through three stages. It starts from cellular structure; then with the strain growth the mixed structure is formed, consisting of cells and subgrains with growing misorientation angles, and, finally, the structure consisting only of crystallites (grains) with mainly high-angle boundaries is formed.…”

Piecewise Model with Two Overlapped Stages for the Structure Formation and Hardening Upon Severe Plastic Deformation in Iron

“…Later studies performed for bcc metals (iron, niobium, molibdenum) which exhibit stacking faults energy more than 140 mJ/mol showed that there are two types of structure are formed in result of HPT treatment. The structure of the first type consists of dislocation cells, and the second type is formed by microcrystallites [14,16,[18][19][20][21]. It is well known, that the formation of dislocation cells is due to the motion and interaction of individual dislocations, while microcrystallites are formed due to rotational deformation modes with the participation of collective disclination effects.…”