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Y. Kohzuki - One of the best experts on this subject based on the ideXlab platform.

  • Study on the interaction between a Dislocation and impurities in KCl:Sr^2+ single crystals by the Blaha effect—Part IV influence of heat treatment on Dislocation density
    Journal of Materials Science, 2009
    Co-Authors: Y. Kohzuki
    Abstract:

    Strain-rate cycling tests associated with ultrasonic oscillation were carried out at 80–239 K for two kinds of KCl:Sr^2+ (0.05 mol.% in the melt) single crystals: one is a quenched specimen and the other an annealed one. In this study, it was found that the density of moving Dislocation is not influenced by the heat treatment. Furthermore, the increase in Forest Dislocation density for the annealed specimen seemed to be remarkable under the compression test, compared with that for the quenched specimen. As a result, the strain-hardening rate increased and the extent of plastic deformation region became short at a given temperature by annealing the quenched specimens. The investigation concerning Forest Dislocation density was conducted on the basis of the $$ \Updelta (\Updelta \tau^{\prime}/\Updelta \ln \dot{\varepsilon })/\Updelta \varepsilon , $$ which will represent the variation of the strain-rate sensitivity due to Dislocation cuttings with shear strain.

  • Study on the interaction between a Dislocation and impurities in KCl:Sr2+ single crystals by the Blaha effect—Part IV influence of heat treatment on Dislocation density
    Journal of Materials Science, 2009
    Co-Authors: Y. Kohzuki
    Abstract:

    Strain-rate cycling tests associated with ultrasonic oscillation were carried out at 80–239 K for two kinds of KCl:Sr2+ (0.05 mol.% in the melt) single crystals: one is a quenched specimen and the other an annealed one. In this study, it was found that the density of moving Dislocation is not influenced by the heat treatment. Furthermore, the increase in Forest Dislocation density for the annealed specimen seemed to be remarkable under the compression test, compared with that for the quenched specimen. As a result, the strain-hardening rate increased and the extent of plastic deformation region became short at a given temperature by annealing the quenched specimens. The investigation concerning Forest Dislocation density was conducted on the basis of the \( \Updelta (\Updelta \tau^{\prime}/\Updelta \ln \dot{\varepsilon })/\Updelta \varepsilon , \) which will represent the variation of the strain-rate sensitivity due to Dislocation cuttings with shear strain.

  • Influence of various divalent impurities on Dislocation density in KCl:Mg2+, Ca2+, Sr2+ or Ba2+ single crystals
    Journal of Materials Science, 2003
    Co-Authors: Y. Kohzuki
    Abstract:

    Single crystals of nominally pure KCl and KCl doped with Mg2+, Ca2+, Sr2+ or Ba2+ were deformed by compression at 77–254 K; during the tests strain-rate cycling was conducted in association with ultrasonic oscillation. The data were analyzed in terms of strain-rate sensitivity ((Δτ′/Δlneέ)) versus stress decrement (Δτ). The curve for KCl doped with the divalent impurities has two bending points and two plateau regions. It is proposed that the variation of strain-rate sensitivity at the second plateau place on the curve with shear strain (Δ(Δτ′/Δlneέ)/Δe) is due to a change in Forest Dislocation density with shear strain. The Forest Dislocation density for the specimens seemed to increase by the divalent additions in the compression test on account of the jogs on the screw Dislocations. It depended on the concentration of impurities and also on the size of impurity in the specimens at a given temperature. Unfortunately, it was not possible to determine whether a change in the size of impurity influences mobile Dislocation density, ρ, from the values of Δρ/Δτ′ for KCl doped with Ca2+, Sr2+ or Ba2+.

Christopher Woodward - One of the best experts on this subject based on the ideXlab platform.

  • Atomistic simulations of intersection cross-slip nucleation in L12 Ni3Al
    Scripta Materialia, 2012
    Co-Authors: Satish I. Rao, Dennis M. Dimiduk, Triplicane A. Parthasarathy, Michael D. Uchic, Christopher Woodward
    Abstract:

    Using atomistic simulations, the authors evaluate the activation barrier for a screw superDislocation to form the Paidar–Pope–Vitek (PPV) locked configuration when intersecting a Forest Dislocation in L1 2 Ni 3 Al, as a function of the superpartial core width. It is shown that the PPV lock is stable at the intersection, unlike when formed along an isolated Dislocation line, and that the activation energy for cross slip at the Forest Dislocation intersection is significantly lower than that for cross slip along an isolated Dislocation.

  • Atomistic Simulations of Intersection Cross-Slip Nucleation in Ll2 Ni3Al (Preprint)
    2011
    Co-Authors: Dennis M. Dimiduk, Satish I. Rao, Michael D. Uchic, Christopher Woodward, Triplicane A. Parthasarathy
    Abstract:

    Abstract : Using atomistic (molecular statics) simulations with embedded atom potentials, we evaluate the activation barrier for a Dislocation to form the PPV lock intersecting a Forest Dislocation in Ll2 Ni3Al as a function of the superpartial core width. The activation energies were obtained by determining equilibrium configurations (energies) when variable pure tensile or compressive stresses are applied along the [111] direction on the partially cross-slipped state. We show that the PPV lock is stable at the intersection, unlike bulk and that the activation energy for cross-slip at the Forest Dislocation intersection is significantly lower than that for cross slip in bulk [energy of two separate constrictions]. These results suggest that cross-slip should be preferentially observed at selected screw Dislocation intersections in Ll2 Ni3Al.

  • The Activated State for Cross-Slip at Screw Dislocation Intersections in Face-Centered Cubic Nickel
    2010
    Co-Authors: Satish I. Rao, Dennis M. Dimiduk, Michael D. Uchic, Christopher Woodward, Jaafar A. El-awady, Triplicane A. Parthasarathy
    Abstract:

    Abstract : We extend our recent work where a screw Dislocation in FCC Ni was found to spontaneously attain a low-energy partially cross-slipped configuration upon intersecting a Forest Dislocation. Using atomistic (molecular statics) simulations with embedded atom potentials, we evaluate the activation barrier for a Dislocation to transform from fully residing on the glide plane to fully residing on the cross-slip plane intersecting a Forest Dislocation. The activation energies were obtained by determining equilibrium configurations (energies) when variable pure tensile or compressive stresses are applied along the direction on the partially cross-slipped state. We show that the activation energy is a factor of 3 - 6 lower than that for cross slip in isolation via the Escaig process. Further, the activation barrier for cross-slip at these intersections is shown to be linearly proportional to (d/b)ln(d/b), as in the Escaig process, where ?d? is the Shockley partial Dislocation spacing and ?b? is the Burgers vector of the screw Dislocation. These results suggest that cross-slip should be preferentially observed at selected screw Dislocation intersections in FCC materials.

  • Activated states for cross-slip at screw Dislocation intersections in face-centered cubic nickel and copper via atomistic simulation
    Acta Materialia, 2010
    Co-Authors: Satish I. Rao, Dennis M. Dimiduk, Triplicane A. Parthasarathy, Michael D. Uchic, Jaafar A. El-awady, Christopher Woodward
    Abstract:

    We extend our recent simulation studies where a screw Dislocation in face-centered cubic (fcc) Ni was found to spontaneously attain a low energy partially cross-slipped configuration upon intersecting a Forest Dislocation. Using atomistic (molecular statics) simulations with embedded atom potentials, we evaluated the activation barrier for a Dislocation to transform from fully residing on the glide plane to fully residing on a cross-slip plane intersecting a Forest Dislocation in both Ni and Cu. The activation energies were obtained by determining equilibrium configurations (energies) when variable pure tensile or compressive stresses were applied along the [1 1 1] direction on the partially cross-slipped state. We show that the activation energy is a factor of 2–5 lower than that for cross-slip in isolation via the Escaig process. The cross-slip activation energies obtained at the intersection in Cu were in reasonable accord with the experimentally determined cross-slip activation energy for Cu. Further, the activation barrier for cross-slip at these intersections was shown to be linearly proportional to (d/b)[ln( ffiffiffi 3 p d/b)] 1/2 , as in the Escaig process, where d is the Shockley partial Dislocation spacing and b is the Burgers

Michael D. Uchic - One of the best experts on this subject based on the ideXlab platform.

  • Atomistic simulations of intersection cross-slip nucleation in L12 Ni3Al
    Scripta Materialia, 2012
    Co-Authors: Satish I. Rao, Dennis M. Dimiduk, Triplicane A. Parthasarathy, Michael D. Uchic, Christopher Woodward
    Abstract:

    Using atomistic simulations, the authors evaluate the activation barrier for a screw superDislocation to form the Paidar–Pope–Vitek (PPV) locked configuration when intersecting a Forest Dislocation in L1 2 Ni 3 Al, as a function of the superpartial core width. It is shown that the PPV lock is stable at the intersection, unlike when formed along an isolated Dislocation line, and that the activation energy for cross slip at the Forest Dislocation intersection is significantly lower than that for cross slip along an isolated Dislocation.

  • Atomistic Simulations of Intersection Cross-Slip Nucleation in Ll2 Ni3Al (Preprint)
    2011
    Co-Authors: Dennis M. Dimiduk, Satish I. Rao, Michael D. Uchic, Christopher Woodward, Triplicane A. Parthasarathy
    Abstract:

    Abstract : Using atomistic (molecular statics) simulations with embedded atom potentials, we evaluate the activation barrier for a Dislocation to form the PPV lock intersecting a Forest Dislocation in Ll2 Ni3Al as a function of the superpartial core width. The activation energies were obtained by determining equilibrium configurations (energies) when variable pure tensile or compressive stresses are applied along the [111] direction on the partially cross-slipped state. We show that the PPV lock is stable at the intersection, unlike bulk and that the activation energy for cross-slip at the Forest Dislocation intersection is significantly lower than that for cross slip in bulk [energy of two separate constrictions]. These results suggest that cross-slip should be preferentially observed at selected screw Dislocation intersections in Ll2 Ni3Al.

  • calculations of intersection cross slip activation energies in fcc metals using nudged elastic band method
    Acta Materialia, 2011
    Co-Authors: S I Rao, Triplicane A. Parthasarathy, D M Dimiduk, Jaafar A Elawady, C Woodward, Michael D. Uchic
    Abstract:

    Abstract The nudged elastic band (NEB) method is used to evaluate activation energies for Dislocation intersection cross-slip in face-centered cubic (fcc) nickel and copper, to extend our prior work which used an approximate method. In this work we also extend the study by including Hirth locks (HL) in addition to Lomer–Cottrell locks and glide locks (GL). Using atomistic (molecular statics) simulations with embedded atom potentials we evaluated the activation barrier for a Dislocation to transform from fully residing on the glide plane to fully residing on the cross-slip plane when intersecting a 120° Forest Dislocation in both Ni and Cu. The initial separation between the screw and the intersecting Dislocation on the (1 1 1) glide plane is varied to find a minimum in the activation energy. The NEB method gives energies that are ∼10% lower than those reported in our prior work. It is estimated that the activation energies for cross-slip from the fully glide plane state to the partially cross-slipped state at the 120° intersection forming GL in Ni and Cu are ∼0.47 and ∼0.65 eV, respectively, and from the fully cross-slip plane state to the partially cross-slipped state forming LC are ∼0.68 and ∼0.67 eV. The activation energies for cross-slip from the fully glide plane state to the partially cross-slipped state at the 120° intersection forming HL in Ni and Cu are estimated to be ∼0.09 and ∼0.31 eV, respectively. These values are a factor of 3–20 lower than the activation energy for bulk cross-slip in Ni and, a factor of 2–6 lower than the activation energy for cross-slip in Cu estimated by Friedel–Escaig analysis. These results suggest that cross-slip should nucleate preferentially at selected screw Dislocation intersections in fcc materials and the activation energies for such mechanisms are also a function of stacking fault energy.

  • The Activated State for Cross-Slip at Screw Dislocation Intersections in Face-Centered Cubic Nickel
    2010
    Co-Authors: Satish I. Rao, Dennis M. Dimiduk, Michael D. Uchic, Christopher Woodward, Jaafar A. El-awady, Triplicane A. Parthasarathy
    Abstract:

    Abstract : We extend our recent work where a screw Dislocation in FCC Ni was found to spontaneously attain a low-energy partially cross-slipped configuration upon intersecting a Forest Dislocation. Using atomistic (molecular statics) simulations with embedded atom potentials, we evaluate the activation barrier for a Dislocation to transform from fully residing on the glide plane to fully residing on the cross-slip plane intersecting a Forest Dislocation. The activation energies were obtained by determining equilibrium configurations (energies) when variable pure tensile or compressive stresses are applied along the direction on the partially cross-slipped state. We show that the activation energy is a factor of 3 - 6 lower than that for cross slip in isolation via the Escaig process. Further, the activation barrier for cross-slip at these intersections is shown to be linearly proportional to (d/b)ln(d/b), as in the Escaig process, where ?d? is the Shockley partial Dislocation spacing and ?b? is the Burgers vector of the screw Dislocation. These results suggest that cross-slip should be preferentially observed at selected screw Dislocation intersections in FCC materials.

  • Activated states for cross-slip at screw Dislocation intersections in face-centered cubic nickel and copper via atomistic simulation
    Acta Materialia, 2010
    Co-Authors: Satish I. Rao, Dennis M. Dimiduk, Triplicane A. Parthasarathy, Michael D. Uchic, Jaafar A. El-awady, Christopher Woodward
    Abstract:

    We extend our recent simulation studies where a screw Dislocation in face-centered cubic (fcc) Ni was found to spontaneously attain a low energy partially cross-slipped configuration upon intersecting a Forest Dislocation. Using atomistic (molecular statics) simulations with embedded atom potentials, we evaluated the activation barrier for a Dislocation to transform from fully residing on the glide plane to fully residing on a cross-slip plane intersecting a Forest Dislocation in both Ni and Cu. The activation energies were obtained by determining equilibrium configurations (energies) when variable pure tensile or compressive stresses were applied along the [1 1 1] direction on the partially cross-slipped state. We show that the activation energy is a factor of 2–5 lower than that for cross-slip in isolation via the Escaig process. The cross-slip activation energies obtained at the intersection in Cu were in reasonable accord with the experimentally determined cross-slip activation energy for Cu. Further, the activation barrier for cross-slip at these intersections was shown to be linearly proportional to (d/b)[ln( ffiffiffi 3 p d/b)] 1/2 , as in the Escaig process, where d is the Shockley partial Dislocation spacing and b is the Burgers

Triplicane A. Parthasarathy - One of the best experts on this subject based on the ideXlab platform.

  • Atomistic simulations of intersection cross-slip nucleation in L12 Ni3Al
    Scripta Materialia, 2012
    Co-Authors: Satish I. Rao, Dennis M. Dimiduk, Triplicane A. Parthasarathy, Michael D. Uchic, Christopher Woodward
    Abstract:

    Using atomistic simulations, the authors evaluate the activation barrier for a screw superDislocation to form the Paidar–Pope–Vitek (PPV) locked configuration when intersecting a Forest Dislocation in L1 2 Ni 3 Al, as a function of the superpartial core width. It is shown that the PPV lock is stable at the intersection, unlike when formed along an isolated Dislocation line, and that the activation energy for cross slip at the Forest Dislocation intersection is significantly lower than that for cross slip along an isolated Dislocation.

  • Atomistic Simulations of Intersection Cross-Slip Nucleation in Ll2 Ni3Al (Preprint)
    2011
    Co-Authors: Dennis M. Dimiduk, Satish I. Rao, Michael D. Uchic, Christopher Woodward, Triplicane A. Parthasarathy
    Abstract:

    Abstract : Using atomistic (molecular statics) simulations with embedded atom potentials, we evaluate the activation barrier for a Dislocation to form the PPV lock intersecting a Forest Dislocation in Ll2 Ni3Al as a function of the superpartial core width. The activation energies were obtained by determining equilibrium configurations (energies) when variable pure tensile or compressive stresses are applied along the [111] direction on the partially cross-slipped state. We show that the PPV lock is stable at the intersection, unlike bulk and that the activation energy for cross-slip at the Forest Dislocation intersection is significantly lower than that for cross slip in bulk [energy of two separate constrictions]. These results suggest that cross-slip should be preferentially observed at selected screw Dislocation intersections in Ll2 Ni3Al.

  • calculations of intersection cross slip activation energies in fcc metals using nudged elastic band method
    Acta Materialia, 2011
    Co-Authors: S I Rao, Triplicane A. Parthasarathy, D M Dimiduk, Jaafar A Elawady, C Woodward, Michael D. Uchic
    Abstract:

    Abstract The nudged elastic band (NEB) method is used to evaluate activation energies for Dislocation intersection cross-slip in face-centered cubic (fcc) nickel and copper, to extend our prior work which used an approximate method. In this work we also extend the study by including Hirth locks (HL) in addition to Lomer–Cottrell locks and glide locks (GL). Using atomistic (molecular statics) simulations with embedded atom potentials we evaluated the activation barrier for a Dislocation to transform from fully residing on the glide plane to fully residing on the cross-slip plane when intersecting a 120° Forest Dislocation in both Ni and Cu. The initial separation between the screw and the intersecting Dislocation on the (1 1 1) glide plane is varied to find a minimum in the activation energy. The NEB method gives energies that are ∼10% lower than those reported in our prior work. It is estimated that the activation energies for cross-slip from the fully glide plane state to the partially cross-slipped state at the 120° intersection forming GL in Ni and Cu are ∼0.47 and ∼0.65 eV, respectively, and from the fully cross-slip plane state to the partially cross-slipped state forming LC are ∼0.68 and ∼0.67 eV. The activation energies for cross-slip from the fully glide plane state to the partially cross-slipped state at the 120° intersection forming HL in Ni and Cu are estimated to be ∼0.09 and ∼0.31 eV, respectively. These values are a factor of 3–20 lower than the activation energy for bulk cross-slip in Ni and, a factor of 2–6 lower than the activation energy for cross-slip in Cu estimated by Friedel–Escaig analysis. These results suggest that cross-slip should nucleate preferentially at selected screw Dislocation intersections in fcc materials and the activation energies for such mechanisms are also a function of stacking fault energy.

  • The Activated State for Cross-Slip at Screw Dislocation Intersections in Face-Centered Cubic Nickel
    2010
    Co-Authors: Satish I. Rao, Dennis M. Dimiduk, Michael D. Uchic, Christopher Woodward, Jaafar A. El-awady, Triplicane A. Parthasarathy
    Abstract:

    Abstract : We extend our recent work where a screw Dislocation in FCC Ni was found to spontaneously attain a low-energy partially cross-slipped configuration upon intersecting a Forest Dislocation. Using atomistic (molecular statics) simulations with embedded atom potentials, we evaluate the activation barrier for a Dislocation to transform from fully residing on the glide plane to fully residing on the cross-slip plane intersecting a Forest Dislocation. The activation energies were obtained by determining equilibrium configurations (energies) when variable pure tensile or compressive stresses are applied along the direction on the partially cross-slipped state. We show that the activation energy is a factor of 3 - 6 lower than that for cross slip in isolation via the Escaig process. Further, the activation barrier for cross-slip at these intersections is shown to be linearly proportional to (d/b)ln(d/b), as in the Escaig process, where ?d? is the Shockley partial Dislocation spacing and ?b? is the Burgers vector of the screw Dislocation. These results suggest that cross-slip should be preferentially observed at selected screw Dislocation intersections in FCC materials.

  • Activated states for cross-slip at screw Dislocation intersections in face-centered cubic nickel and copper via atomistic simulation
    Acta Materialia, 2010
    Co-Authors: Satish I. Rao, Dennis M. Dimiduk, Triplicane A. Parthasarathy, Michael D. Uchic, Jaafar A. El-awady, Christopher Woodward
    Abstract:

    We extend our recent simulation studies where a screw Dislocation in face-centered cubic (fcc) Ni was found to spontaneously attain a low energy partially cross-slipped configuration upon intersecting a Forest Dislocation. Using atomistic (molecular statics) simulations with embedded atom potentials, we evaluated the activation barrier for a Dislocation to transform from fully residing on the glide plane to fully residing on a cross-slip plane intersecting a Forest Dislocation in both Ni and Cu. The activation energies were obtained by determining equilibrium configurations (energies) when variable pure tensile or compressive stresses were applied along the [1 1 1] direction on the partially cross-slipped state. We show that the activation energy is a factor of 2–5 lower than that for cross-slip in isolation via the Escaig process. The cross-slip activation energies obtained at the intersection in Cu were in reasonable accord with the experimentally determined cross-slip activation energy for Cu. Further, the activation barrier for cross-slip at these intersections was shown to be linearly proportional to (d/b)[ln( ffiffiffi 3 p d/b)] 1/2 , as in the Escaig process, where d is the Shockley partial Dislocation spacing and b is the Burgers

William A. Curtin - One of the best experts on this subject based on the ideXlab platform.

  • Solute Strengthening of both Mobile and Forest Dislocations: the Origin of Dynamic Strain Aging in fcc Metals
    2015
    Co-Authors: M.a. Soare, William A. Curtin
    Abstract:

    A full rate-dependent constitutive theory for dynamic strain aging is developed based on two key ideas. The first idea is that both solute strengthening and Forest strengthening must exist and must exhibit aging phenomena; neither alone can yield negative strain-rate-sensitivity as shown in a companion paper. The second idea is that a single physical aging mechanism, cross-core diffusion within a Dislocation core, controls the aging of both the solute and Forest strengthening mechanisms. All of the material parameters in the model, aside from Forest Dislocation density evolution parameters, are derivable from atomistic-scale studies so that the theory contains essentially no adjustable parameters. In application to a variety of Al-Mg alloys, the model predicts the steady-state stress/strain/strain-rate/temperature/concentration dependent material response, including negative strain rate sensitivity, in qualitative and quantitative agreement with available experiments. With no additional assumptions, the model also reveals the origin of non-additivity of solute and Forest strengthening and explains the observed transient stress behavior in strain-rate jump tests. The theory thus captures essentially all aspects of the dynamic aging phenomenon. With such detailed success, the proposed constitutive model can be incorporated into numerical simulations of the deformation of realistic material components under complex loading conditions

  • Solute strengthening of both mobile and Forest Dislocations: The origin of dynamic strain aging in fcc metals
    Acta Materialia, 2008
    Co-Authors: M.a. Soare, William A. Curtin
    Abstract:

    A full rate-dependent constitutive theory for dynamic strain aging is developed based on two key ideas. The first idea is that both solute strengthening and Forest strengthening must exist and must exhibit aging phenomena. The second idea is that a single physical aging mechanism, cross-core diffusion within a Dislocation core, controls the aging of both the solute and Forest strengthening mechanisms. All the material parameters in the model, apart from Forest Dislocation density evolution parameters, are derivable from atomistic-scale studies so that the theory contains essentially no adjustable parameters. The model predicts the steady-state stress/strain/strain-rate/temperature/concentration dependent material response for a variety of Al-Mg alloys, including negative strain-rate sensitivity, in qualitative and quantitative agreement with available experiments. The model also reveals the origin of non-additivity of solute and Forest strengthening, and explains observed non-standard transient stress behavior in strain-rate jump tests. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.