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154. Grain-size effect on the deformation mechanisms of nanostructured copper processed by high-pressure torsion.

Author

Liao, X.Z., Zhao, Y.H., Zhu, Y.T., Valiev, R.Z., and Gunderov, D.V.

Subjects
DEFORMATIONS (Mechanics), TORSION, STRAINS & stresses (Mechanics), HIGH pressure (Science), DISLOCATIONS in crystals, CRYSTAL grain boundaries
Abstract

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]

Published
2004
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186. Microstructural features of failure surfaces and low-temperature mechanical properties of Ti-6Al-4V ELI ultra-fine grained alloy

Author

Tabachnikova, E.D., Podolskiy, A.V., Smirnov, S.N., Csach, K., Miskuf, J., Saitova, L.R., Semenova, I.P, Valiev, R.Z., and Bengus, V.Z.

Subjects
Научно-технический раздел
Abstract

Microstructural regularities of failure surfaces and low-temperature mechanical characteristics in quasistatic uniaxial tension and compression have been studied for ultra-fine grained structural states of Ti-6Al-4V ELI alloy processed by equal channel angular pressing. Values of the yield stress and uniform strain at 300, 77, and 4.2 K have been compared for structural states of the Ti-6Al-4V ELI alloy that differ in the average grain size and the morphology of α and β phases. Statistical distributions of dimple sizes on the failure surfaces have been studied for different structural states and temperatures. Исследованы особенности микроструктуры поверхностей излома и низкотемпературные механические свойства сверхмелкозернистого ELI-сплава Ti-6Al-4V, обработанного методом равноканального углового прессования, при квазистатическом одноосном растяжении и сжатии. Проведено сравнение значений предела текучести и однородной деформации, полученных при температурах 300, 77 и 4,2 К для разных структурных состояний ELI-сплава ТІ-6А1-4У с различным средним размером зерна и морфологией α- и β-фаз. Исследовано статистическое распределение размеров ямок на поверхностях излома при различных структурных состояниях и температурах.

Published
2008

187. Superplastic behavior of ultrafine-grained Ti−6Al−4V ELI alloy produced by severe plastic deformation

Author

Semenova, I.P., Saitova, L.R., Raab, G.I., and Valiev, R.Z.

Abstract

This paper reports the results of investigation of mechanical behavior of the ultrafinegrained (UFG) Ti-6Al-4V alloy processed by equal-channel angular pressing (ECAP) and extrusion at temperatures in a range of 500−800°C. The UFG alloy reveals superplastic behavior at relatively low temperatures down to 600°C (elongation 240%). The features of microstructure change of the UFG alloy under superplastic straining conditions that contribute to additional strengthening of the alloy are shown.

Published
2006

188. The new trends in SPD processing to fabricate bulk nanostructured materials

Author

Valiev, R.Z.

Abstract

During the last decade severe plastic deformation (SPD) has become a widely known method of materials processing used for fabrication of ultrafine-grained materials with attractive properties. Nowadays SPD processing is rapidly developing and is on the verge of a transition from lab-scale research to commercial production. This paper focuses on several new trends in the development of SPD techniques for effective grain refinement, including those for commercial alloys, and presents new SPD processing routes to produce bulk nanocrystalline materials.

Published
2006

195. Backpressure at ECAP as a way for decreasing grain size and increasing ductility of UFG materials

Author

Raab., G.I, Krasilnikov, N.A., and Valiev, R.Z.

Abstract

The investigation of the backpressure effect during equal-channel angular pressing (ECAP) on formation of ultrafine-grained (UFG) structure in pure copper has revealed that the increased hydrostatic pressure can contribute to formation of a more homogeneous microstructure with finer grains. ECAP with backpressure also exerts a favorable effect on strength and ductility characteristics of the UFG material.

Published
2003

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