Anomalous production of vacancy clusters and the possibility of plastic deformation of crystalline metals without dislocations

Kiritani, M.; Satoh, Yuhki; Kizuka, Y.; Arakawa, Kazuto; Ogasawara, Yasokichi; Arai, Shigeo; Shimomura, Y.

doi:10.1080/095008399176616

Cited by 126 publications

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“…As the grain boundaries have an open structure compared with the crystalline lattice, they usually show reduced elastic modulus relative to the bulk material [84][85][86]. Another possible explanation for this observation is that SPD-processed metals have an extraordinarily high concentration of excess vacancies [87,88]. In fact, it has been shown that HPT can increase the vacancy concentration of a metal to the level found immediately below the melting point of the metal, $10 À4 .…”

Section: Discussionmentioning

confidence: 99%

Microstructure and mechanical properties at different length scales and strain rates of nanocrystalline tantalum produced by high-pressure torsion

et al. 2011

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Wei, Q.; Pan, Z. L.; Wu, X. L.; Schuster, B. E.; Kecdkes, L. J.; and Valiev, R. Z., "Microstructure and mechanical properties at different length scales and strain rates of nanocrystalline tantalum produced by high-pressure torsion" (2011 AbstractFully dense, nanocrystalline tantalum (average grain size as small as $40 nm) has been processed for the first time by high-pressure torsion. High-resolution transmission electron microscopy reveals non-equilibrium grain boundaries and grains decorated with high-density dislocations. Microhardness measurements and instrumented nanoindentation experiments indicate that the mechanical property is quite uniform except for the central area of the disks. Nanoindentation experiments at different strain rates suggest that the strain rate sensitivity of nanocrystalline tantalum is increased compared to the coarse-and ultrafine-grained counterparts and is accompanied by an activation energy of the order of a few $b 3 (b is the magnitude of the dislocation Burgers vector), implying a shift in the plastic deformation mechanism from the screw dislocation dominated regime. We thus infer the plastic deformation mechanisms of nanocrystalline body-centered cubic (bcc) and face-centered cubic metals converge. To examine the stress-strain behavior, we have used microcompression to measure the compressive stress-strain curves on microscale pillars fabricated by focused ion beam technique. Yield strength as high as 1.6 GPa has been observed. High-strain rate behavior has been investigated using a miniature Kolsky bar system. We have found that at high-strain rates the nanocrystalline tantalum specimens exhibit adiabatic shear banding, a dynamic plastic deformation mode common to many ultrafine-grained and all nanocrystalline bcc metals.

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Section: Discussionmentioning

confidence: 99%

Microstructure and mechanical properties at different length scales and strain rates of nanocrystalline tantalum produced by high-pressure torsion

et al. 2011

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“…Kiritani et al [1][2][3][4][5] have reported a generation of many vacancy clusters at fractured tips of thin foils of fcc metals. Immediately before the fracture, they also observed that the elastic strain of the sawtooth-like torn portion is more than 10% in Au, Cu and Ni by electron microscopy diffraction analysis.…”

Section: Introductionmentioning

confidence: 99%

Computer Simulation of Formation Energy and Migration Energy of Vacancies under High Strain in Cu

et al. 2004

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Recently it has been reported that many vacancy clusters are generated at sawtooth-like fractured tips of thin foils. The elastic strain of the torn portion is more than 10% before the fracture, which is expected to cause the generation of many vacancy clusters. In this paper, the formation and migration behaviors of vacancies in Cu under high elastic strain from 10% compression to 20% elongation were studied by computer simulation using the effective medium theory (EMT) potential. The model lattice was elastically deformed along the h110i and h100i directions. Poisson's ratio was determined to minimize the total energy. After full relaxation of the lattice by the static method (Newton-Raphson method) under fixed boundary conditions, a vacancy was introduced and the change of the total energy (formation energy) was calculated. The migration energy of vacancies was obtained as the total energy difference between the model lattice with an atom at the lattice point and the atom at the saddle point. High strain dependence of these energies is obtained. For example, the formation and the migration energies of vacancies are 1.21 eV and 0.79 eV in the absence of deformation, respectively. The formation energy in the h100i deformation is 1.09 eV and 1.13 eV by 10% compression and 10% elongation, respectively. The migration energies and the migration distances vary with the migration direction. For example, the migration energy for the shortest migration distance in the h100i deformation is reduced to 0.45 eV and 0.26 eV by 10% compression and 10% elongation, respectively. While that for the longest migration distance increases to 1.29 eV by 10% compression. These results are explained by the configuration of neighboring atoms nearest to the vacancy.

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“…[1][2][3][4][5] Materials scientists have emphasized the role of high-speed deformation in engineering applications, mainly the relationship between deformationinduced microstructures and residual mechanical properties. The complex interrelationships between stress, stress state, strain, strain rate and temperature, have been used for pursuing a better design of materials with the objective of postponing a period of use.…”

Section: Introductionmentioning

confidence: 99%

“…For more details the readers are referred to Mayers. 13) Recently, Kiritani et al 1,2) reported that a large number of vacancies were produced during high-speed heavy plastic deformation of thin foils of fcc metals. They observed a large density of vacancy defect clusters but very low dislocation densities in the foils after deformation.…”

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confidence: 99%

Microstructures of High-speed Deformation in 0.20% C Carbon Steel Induced by High-current Pulsed Electron Beams Irradiation

Zhao

et al. 2010

ISIJ Int.

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Anomalous production of vacancy clusters and the possibility of plastic deformation of crystalline metals without dislocations

Cited by 126 publications

References 0 publications

Microstructure and mechanical properties at different length scales and strain rates of nanocrystalline tantalum produced by high-pressure torsion

Microstructure and mechanical properties at different length scales and strain rates of nanocrystalline tantalum produced by high-pressure torsion

Computer Simulation of Formation Energy and Migration Energy of Vacancies under High Strain in Cu

Microstructures of High-speed Deformation in 0.20% C Carbon Steel Induced by High-current Pulsed Electron Beams Irradiation

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