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Woei-shyan Lee - One of the best experts on this subject based on the ideXlab platform.

  • Dynamic Deformation Behaviour and Dislocation Substructure of AZ80 Magnesium Alloy over a Wide Range of Temperatures
    EPJ Web of Conferences, 2018
    Co-Authors: Woei-shyan Lee, Cheng Wen Chou
    Abstract:

    The high strain rate deformation behaviour and Dislocation Substructure of AZ80 magnesium alloy are investigated at strain rates of 8x102 s-1, 1.5x103 s-1 and 2.2x103 s-1 and temperatures of-100 ºC, 25 ºC and 300 ºC using a compressive split-Hopkinson pressure bar system. The flow stress, work hardening coefficient, strain rate sensitivity and temperature sensitivity all increase with increasing strain rate or decreasing temperature. Moreover, the dynamic deformation behaviour is well described by the Zerilli-Armstrong hcp constitutive equation. Transmission electron microscopy observations show that the Dislocation density increases with a higher strain rate or a lower temperature. Finally, the flow stress varies linearly with the square root of the Dislocation density in accordance with the Bailey-Hirsch model.

  • Temperature-dependent variation in dynamic deformation behaviour and Dislocation Substructure in AZ80 magnesium
    Materials Science and Technology, 2017
    Co-Authors: Woei-shyan Lee, Cheng Wen Chou
    Abstract:

    The dynamic deformation behaviour and Dislocation Substructure of AZ80 magnesium alloy are investigated at strain rates of 8 × 102, 1.5 × 103 and 2.2 × 103 s−1 and temperatures of −100, 25 and 300°C using a compressive split-Hopkinson pressure bar system. The flow stress, work hardening coefficient, strain rate sensitivity and temperature sensitivity all increase with increasing strain rate or decreasing temperature. Moreover, the dynamic deformation behaviour is well described by the Zerilli–Armstrong hexagonal close packed (hcp) constitutive equation. Catastrophic failure occurs at all three temperatures under strain rates of 1.5 × 103 and 2.2 × 103 s−1. Transmission electron microscopy observations show that the Dislocation density increases with a higher strain rate or a lower temperature. Finally, the flow stress varies linearly with the square root of the Dislocation density in accordance with the Bailey–Hirsch model.This paper is part of a thematic issue on Light Alloys.

  • effects of directional grain structure on impact properties and Dislocation Substructure of 6061 t6 aluminium alloy
    Materials Science and Technology, 2014
    Co-Authors: Woei-shyan Lee, M H Liu
    Abstract:

    AbstractThe effects of the grain structure direction on the impact properties and Dislocation Substructure of 6061-T6 aluminium alloy are investigated under room temperature conditions and strain rates of 1×103, 3×103 and 5×103 s−1 using a split-Hopkinson pressure bar system. The impact tests are performed using specimens machined from rolled 6061-T6 plates in the longitudinal, transverse and through thickness directions respectively. The results show that for all specimens, the flow stress increases with increasing strain rate. Furthermore, for all strain rates, the highest flow stress occurs in the transverse specimen. For strain rates of 1×103 and 3×103 s−1, the flow stress in the through thickness specimen is greater than that in the longitudinal specimen. However, at a strain rate of 5×103 s−1, the flow stress in the longitudinal specimen is higher than that in the through thickness specimen due to a greater Dislocation multiplication rate. For all three grain structure directions, the strain rate se...

  • effect of directional grain structure and strain rate on impact properties and Dislocation Substructure of 6061 t6 aluminum alloy
    Key Engineering Materials, 2014
    Co-Authors: Woei-shyan Lee, M H Liu
    Abstract:

    The effect of directional grain structure and strain rate on the impact properties and Dislocation Substructure of 6061-T6 aluminum alloy is studied. Impact tests are performed at strain rates ranging from 1x103 to 5x103s-1 using a split Hopkinson pressure bar system. Cylindrical specimens are prepared from the rolled plates in longitudinal direction, transverse direction and through-thickness direction, respectively. The results show that the flow stress is strongly dependent on the strain rate and displays complex variations with grain structure direction. The flow stress increases with increasing strain rate. For all tested strain rates, the flow stress is the highest in the transverse specimen, followed by the through-thickness specimen and longitudinal specimen. However, at the strain rate of 5x103s-1, the flow stress in longitudinal specimen is higher than that in through-thickness specimen due to the change of Dislocation multiplication rate. The plastic flow occurs within the deformation regions, and becomes more pronounced at high strain rates, especially for the longitudinal specimen. Dislocation density increases markedly with increasing strain rate. Strengthening effect is the highest in the transverse specimen, followed by the longitudinal specimen and through-thickness specimen.

  • Impact Deformation and Dislocation Substructure of Ti-6Al-7Nb Biomedical Alloy
    Applied Mechanics and Materials, 2014
    Co-Authors: Woei-shyan Lee, Chia Wei Chen
    Abstract:

    The high temperature deformation and Dislocation Substructure of Ti-6Al-7Nb biomedical alloy are investigated under high strain rate loading conditions using a split-Hopkinson pressure bar. Impact tests are performed at strain rates ranging from 1x103s-1 to 3x103s-1 and temperatures of 300°Cand 700°C, respectively. The experimental results show that the flow stress, work hardening coefficient and strain rate sensitivity all increase with increasing strain rate, but decrease with increasing temperature. Transmission electron microscopy observations reveal that the Dislocation density increases with increasing strain rate, but decreases with increasing temperature. A pronounced thermal softening effect is observed in the specimens deformed at 700°C due to the rapid annihilation of the Dislocations. However, a work hardening effect occurs at higher strain rates and lower temperatures due to an enhanced degree of Dislocation multiplication and tangling. Finally, a linear relationship is observed between the square root of the Dislocation density and the flow stress.

Chia Wei Chen - One of the best experts on this subject based on the ideXlab platform.

  • Impact Deformation and Dislocation Substructure of Ti-6Al-7Nb Biomedical Alloy
    Applied Mechanics and Materials, 2014
    Co-Authors: Woei-shyan Lee, Chia Wei Chen
    Abstract:

    The high temperature deformation and Dislocation Substructure of Ti-6Al-7Nb biomedical alloy are investigated under high strain rate loading conditions using a split-Hopkinson pressure bar. Impact tests are performed at strain rates ranging from 1x103s-1 to 3x103s-1 and temperatures of 300°Cand 700°C, respectively. The experimental results show that the flow stress, work hardening coefficient and strain rate sensitivity all increase with increasing strain rate, but decrease with increasing temperature. Transmission electron microscopy observations reveal that the Dislocation density increases with increasing strain rate, but decreases with increasing temperature. A pronounced thermal softening effect is observed in the specimens deformed at 700°C due to the rapid annihilation of the Dislocations. However, a work hardening effect occurs at higher strain rates and lower temperatures due to an enhanced degree of Dislocation multiplication and tangling. Finally, a linear relationship is observed between the square root of the Dislocation density and the flow stress.

  • high temperature impact properties and Dislocation Substructure of ti 6al 7nb biomedical alloy
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2013
    Co-Authors: Woei-shyan Lee, Chia Wei Chen
    Abstract:

    Abstract The high temperature deformation and Dislocation Substructure of Ti–6Al–7Nb biomedical alloy are investigated under high strain rate loading conditions using a split-Hopkinson pressure bar. Impact tests are performed at strain rates ranging from 1×10 3  s −1 to 3×10 3  s −1 and temperatures of 300 °C and 700 °C, respectively. The experimental results show that the flow stress, work hardening coefficient and strain rate sensitivity all increase with increasing strain rate, but decrease with increasing temperature. Moreover, the fracture observations reveal that the Ti–6Al–7Nb specimens fail predominantly as the result of intensive localised shearing. The fracture surfaces of the deformed specimens contain both cleavage structures and dimple-like structures. Transmission electron microscopy observations reveal that the Dislocation density increases with increasing strain rate, but decreases with increasing temperature. A pronounced thermal softening effect is observed in the specimens deformed at 700 °C due to a rapid annihilation of the Dislocations. However, a work hardening effect occurs at higher strain rates and lower temperatures due to an enhanced degree of Dislocation multiplication and tangling. Finally, a linear relationship is observed between the square root of the Dislocation density and the flow stress.

V. E. Gromov - One of the best experts on this subject based on the ideXlab platform.

  • change of deformation characteristics and Dislocation Substructure of nonferrous metals under influence of magnetic field
    IOP Conference Series: Materials Science and Engineering, 2016
    Co-Authors: D. V. Zagulyaev, Irina Komissarova, S V Konovalov, V V Shlyarov, E A Anuchina, V. E. Gromov
    Abstract:

    The objects of the study were polycrystalline copper of M00b grade and commercially pure titanium BT1-0. Microindentation was carried out on the samples of titanium BT1-0 in the initial state, immediately after magnetic field exposure of 0.4 T and after certain time intervals. The defect Substructure of cooper samples M00b, subjected to loading to failure in the creep mode under the influence of magnetic field of 0.35 T and without it, was investigated by the methods of electron diffraction microscopy. It was revealed that the effect of magnetic field exposure on commercially pure titanium BT1-0 leads to the decrease in microhardness with the subsequent stabilization during the time that depends on the processing parameters. And the effect of the magnetic field exposure on copper during the process of creeping results in the redistribution of Dislocation Substructure types. Also, there are changes in quantitative characteristics of Dislocation Substructures.

  • Regularities of varying the Dislocation Substructure of copper under creep in the magnetic field
    Russian Journal of Non-Ferrous Metals, 2015
    Co-Authors: Sergey Konovalov, N. G. Yaropolova, Yurii F. Ivanov, D. V. Zagulyaev, Irina Komissarova, V. E. Gromov
    Abstract:

    The object of the study is polycrystalline copper of M006 brand. The Dislocation Substructure (DSS), which is formed in copper under the destruction in creep conditions in a magnetic field of 0.35 T, was studied by diffraction electron microscopy. The Substructure of the initial state of copper is characterized by the presence of the following DSS types: chaotically distributed Dislocations (56%), a cellular Substructure of various degrees of perfection (36%), a netlike Substructure (5%), a band Substructure (3%), Dislocation bundles (3%), and broken subboundaries (2%). It is established that the peculiarities in the quantitative ratio of DSS types manifest themselves under destruction in the magnetic field. Notably, the main DSS type near the destruction zone in copper deformed under creep conditions is the subgrain structure. The application of the magnetic field leads to a decrease in the relative content of the subgrain structure in copper by almost a factor of 2. It is shown that the magnetic-field effect retards the transformation rate of the Dislocation Substructure under creep of copper, which leads to an increase in strength characteristics.

  • formation of gradients of structure phase composition and Dislocation Substructure in differentially hardened rails
    Nanotechnologies in Russia, 2014
    Co-Authors: V. E. Gromov, Yu F Ivanov, K V Morozov, K V Volkov, S V Konovalov
    Abstract:

    A layer by layer analysis of rails, differentially hardened in various modes, has been carried out using transmission electron microscopy on various scale levels. It has been shown that the differential hardening of rails is accompanied by the formation of a morphologically different structure, which is formed according to the diffusion mechanism of γ-α transformation and consisting of plate perlite grains, free ferrite grains, and grains of a ferrite-carbide mixture. The gradient character of modifications of structure, phase composition, and Dislocation Substructure parameters along the cross section of rail head has been established. It has been revealed that the interfaces between globular cementite particles and the matrix are the most dangerous stress concentrators.

  • Formation of structure-phase states and Dislocation Substructures during thermomechanical hardening of Fe–0.09C–2Mn–1Si steel
    Russian Physics Journal, 2012
    Co-Authors: V. B. Kosterev, Yu F Ivanov, V. E. Gromov, O. Yu. Efimov, Sergey Konovalov
    Abstract:

    3 Results of investigations of the structure-phase state and Dislocation Substructure formation during thermomechanical hardening of Fe-0.09C-2Mn-1Si steel in different regimes are presented. Methods of transmission electron microscopy reveal the formation of gradient states characterized by regular changes of the structure, phase composition, types, and parameters of the Dislocation Substructures over the structure cross section.

  • Dislocation Substructure evolution on Al creep under the action of the weak electric potential
    Materials Science and Engineering: A, 2010
    Co-Authors: V. E. Gromov, O. A. Stolboushkina, Yu F Ivanov, Sergey Konovalov
    Abstract:

    The Dislocation Substructure evolution on Al creep under the action of the weak electric potential is established by methods of transmission diffraction electron microscopy. It is shown that change of the electrical potential of the Al sample surface is accompanied by the increase of Dislocation Substructure self-organization degree.

Sergey Konovalov - One of the best experts on this subject based on the ideXlab platform.

  • An Impact of the Magnetic Field on the Fine Copper Structure under Creep Failure Conditions
    2016
    Co-Authors: Sergey Konovalov, N. G. Yaropolova, Dmitry Zaguyliaev, Yurii Ivanov, Victor Gromov
    Abstract:

    Abstract. An impact of a weak magnetic field on changes in the Dislocation Substructure of commercially pure copper exposed to stressing up to destruction under creep conditions was investigated. It was established that a magnetic field action on a metal subjected to creep resulted in the formation of a band Dislocation Substructure. In some cases grains with the Dislocation chaos structure or cellular and grid Substructures were revealed. In addition, quantitative differences in the Dislocation Substructure characteristics were also identified. A gradient nature of changes in the number of stress concentrators when moving away from the failure surface was defined. It was shown that the density of bend extinction contours characterizing the number of stress concentrators in the material decreased when moving away from the failure surface

  • Regularities of varying the Dislocation Substructure of copper under creep in the magnetic field
    Russian Journal of Non-Ferrous Metals, 2015
    Co-Authors: Sergey Konovalov, N. G. Yaropolova, Yurii F. Ivanov, D. V. Zagulyaev, Irina Komissarova, V. E. Gromov
    Abstract:

    The object of the study is polycrystalline copper of M006 brand. The Dislocation Substructure (DSS), which is formed in copper under the destruction in creep conditions in a magnetic field of 0.35 T, was studied by diffraction electron microscopy. The Substructure of the initial state of copper is characterized by the presence of the following DSS types: chaotically distributed Dislocations (56%), a cellular Substructure of various degrees of perfection (36%), a netlike Substructure (5%), a band Substructure (3%), Dislocation bundles (3%), and broken subboundaries (2%). It is established that the peculiarities in the quantitative ratio of DSS types manifest themselves under destruction in the magnetic field. Notably, the main DSS type near the destruction zone in copper deformed under creep conditions is the subgrain structure. The application of the magnetic field leads to a decrease in the relative content of the subgrain structure in copper by almost a factor of 2. It is shown that the magnetic-field effect retards the transformation rate of the Dislocation Substructure under creep of copper, which leads to an increase in strength characteristics.

  • Magnetic Field Effect on Creep of Polycrystalline Copper
    Advanced Materials Research, 2015
    Co-Authors: Sergey Konovalov, N. G. Yaropolova, Dmitry Zaguyliaev, Yurii F. Ivanov, Victor Gromov, A. P. Semin
    Abstract:

    The constant magnetic field effect (B≤0.6 T) on creep of polycrystalline copper and its Dislocation Substructure has been established. The correlation of creep rate to time up to failure has been determined. The magnetic field effect on change of Dislocation Substructure parameters depending on the distance to the surface of failure (at a distance of 2, 4, 7, 10 and 20 mm from the surface of failure) under creep has been studied. It has been shown that magnetic field affects greatly the redistribution of Dislocation Substructure types and their scalar density of Dislocations. The magnetic field effect on polycrystalline copper is connected with magneto-induction relaxation of Dislocation structure.

  • Formation of structure-phase states and Dislocation Substructures during thermomechanical hardening of Fe–0.09C–2Mn–1Si steel
    Russian Physics Journal, 2012
    Co-Authors: V. B. Kosterev, Yu F Ivanov, V. E. Gromov, O. Yu. Efimov, Sergey Konovalov
    Abstract:

    3 Results of investigations of the structure-phase state and Dislocation Substructure formation during thermomechanical hardening of Fe-0.09C-2Mn-1Si steel in different regimes are presented. Methods of transmission electron microscopy reveal the formation of gradient states characterized by regular changes of the structure, phase composition, types, and parameters of the Dislocation Substructures over the structure cross section.

  • Dislocation Substructure Gradient Formation in Aluminum by Creep under Weak Potential
    Arabian Journal for Science and Engineering, 2011
    Co-Authors: Sergey Konovalov, O. A. Stolboushkina, Yu F Ivanov, Victor Gromov
    Abstract:

    Transmission diffraction electron microscopy of thin foils was used to study the Dislocation Substructure gradient of aluminum destroyed during creep. Creep under +1 V potential resulted in the formation of a Dislocation Substructure gradient, which was observed as a regular change in quantitative structural characteristics upon moving away from the sample fracture surface.

Yu F Ivanov - One of the best experts on this subject based on the ideXlab platform.