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The unique nonuniform deformation characteristic of high-pressure torsion was used to produce nanostructures with systematically varying grain sizes in a copper disk, which allows us to study the grain-size effect on the deformation mechanisms in nanostructured copper using a single sample. The as-processed copper disk has 100–200 nm grains near its center and 10–20 nm grains at its periphery. High densities of full dislocations (2×1016/m2) were distributed nonuniformly in large grains, implying that dislocation slip is the dominant deformation mechanism. With increasing dislocation density, the dislocations accumulated and rearranged, forming elongated nanodomains. The originally formed nanodomains remain almost the same crystalline orientation as their parent large grains. Further deformation occurred mainly through partial dislocation emissions from nanodomain boundaries, resulting in high density of nanotwins and stacking faults in the nanodomains. The elongated nanodomains finally transformed into equiaxed nanocrystalline grains with large-angle grain boundaries. The results suggest that grain boundary rotation and grain boundary sliding might play a significant role in the formation of large-angle grain boundaries in nanocrystalline grains. These experimental results show that different deformation mechanisms operate at different length scales and confirm unambiguously the deformation mechanisms of nanocrystalline grains predicted by molecular dynamic simulations. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Focuses on a study conducted on an ultrafine-grained (UFG) Ni sample which was processed by severe plastic deformation, using x-ray diffraction investigations in a temperature ranging from 85 to 295 K. Details on the thermal behavior of atoms in UFG Ni; Information on the temperature dependence of the lattice parameter; Calibration of the geometrical conditions of the instrument.

Cast Co-5.6 wt% Cu and Co-13.6 wt% Cu alloys were subjected to severe plastic deformation (SPD) by high-pressure torsion (HPT). The HPT treatment drastically decreases the size of the Co grains (from 20 µm to 100 nm) and the Cu precipitates (from 2 µm to 10 nm). As a result, the coercivity Hc of both the alloys radically increases. The saturation magnetization, Ms, remains almost unchanged. Thus, SPD of the bulk samples opens the way for drastic increase in the coercivity for the Co-based alloys. [ABSTRACT FROM AUTHOR]

The process of equichannel angular pressing (ECAP) is studied with the aim of fabricating large-size preforms with a diameter of 40 mm and a length of 160 mm from alloy 1421 to be used for forming sheets by subsequent warm rolling. Special features of the microstructure and optimum modes of superplasticity and mechanical properties of sheets with ultrafine-grain (UFG) structure are considered. [ABSTRACT FROM AUTHOR]

Nanostructured materials should present a good resistance to irradiation because the large volume fraction of grain boundaries can be an important sink for radiation-induced defects. The objective of the present study is to experimentally investigate the irradiation impact on the microstructure and mechanical properties in nanostructured materials. Nickel and Cu-0.5 Al2O3 specimens were synthesized by electro deposition (ED) and severe plastic deformation (SPD). Mean grain size of the unirradiated specimen is about 30nm for the ED Ni and about 115 nm for the SPI) Ni, 590 MeV proton irradiation and 840 kcV nickel ion irradiation were conducted at room temperature. Vickers hardness measurements and transmission electron microscope observation were performed to examine the impact of irradiation on nanocrystalline materials. It appears that the irradiation induced microstructure in Ni and in Cu-0.5Al2O3, which leads to hardening, consists exclusively of stacking fault tetrahedra. Their density appears much lower than in the case of coarser grained material. These results, experimentally showing the resistance of nanostructured material to radiation damage, are presented here. [ABSTRACT FROM AUTHOR]

Shows the conveniences for the preparation of bulk nanocrystalline materials by severe plastic deformation (SPD) using a Ti-Ni-Cu alloy possessing the shape-memory effect and a Nd-Fe-B alloy, which is a hard magnetic material. Indication that the SPD of amorphous rapidly quenched alloys results in an abrupt decrease in their crystallization temperature; Formation of finer nanocrystalline structure.