Saturation of Fragmentation During Severe Plastic Deformation

Abstract

In this review, we focus on the saturation microstructure that evolves during severe plastic deformation (SPD). These nanocrystalline or ultrafine-grained microstructures consist predominantly of high-angle boundaries, although low-angle boundaries are also present. Deformation temperature, alloying, and strain path are the dominant factors controlling the saturation grain size in single-phase materials. The saturation grain size decreases significantly with decreasing deformation temperature, although the dependency is stronger at medium homologous temperatures and less in the low-temperature regime. The saturation microstructure is sensitive to strain rate at medium temperatures and less so at low temperatures. The addition of alloying elements to pure metals also reduces the saturation grain size. The results indicate that grain boundary migration is the dominant process responsible for the limitation in refinement by SPD. Therefore, second-phase particles of the nanometer scale can stabilize even finer microstructures. This mechanism of stabilization of the microstructure is an effective tool for overcoming the limit in refinement of single-phase materials by SPD. The improved thermal stability of the obtained nanostructures is another benefit of the introduction of second-phase particles.

Direct measurement of vacancy relaxation by dilatometry

“…A model system which fulfills these requirements is given with bulk nanocrystalline metals prepared by high-pressure torsion (HPT). 11 HPT-Ni is particularly well-suited owing to the following aspects: Besides a macroscopic sample dimensions (condition (i)) and ultrafine crystallite sizes in the regime of 100 to 200 nm (condition (iv)), HPT-processing of Ni yields elongated crystallites with elongation axis lying in tangential direction of the HPT-disk (condition (ii), see Figs. 2 and 1) [12][13][14].…”

“…For grain refinement by high-pressure torsion, 11 5 revolutions with a quasi-hydrostatic pressure of 2.2 GPa were applied yielding disks with a diameter of 30 mm and a height of ca. 8 mm (Fig.…”

Plastic Deformation of BaTiO3Ceramics by High-pressure Torsion and Changes in Phase Transformations, Optical and Dielectric Properties

“…It should be noted that the occurrence of steady states at large strains, as in Figure 1(b), has been reported in many other materials. [35][36][37] The BTO microstructure at the steady state after HPT processing is shown in Figure 2. Nanograins form after processing, in agreement with earlier studies of grain refinement by severe straining.…”

Structural anisotropy in equal-channel angular extruded nickel revealed by dilatometric study of excess volume

“…It is also well documented that the degree of grain refinement for ECAP-deformation is not as high as for HPT-deformation [22]. As a reason therefore may be considered the reduced equivalent strain, i. e., 7.5 for the present ECAP-deformation, which is below the saturation regime achieved with the HPT-deformation applied here [27].…”