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Terence G. Langdon - One of the best experts on this subject based on the ideXlab platform.

  • evolution of plasticity strain rate sensitivity and the underlying Deformation Mechanism in zn 22 al during high pressure torsion
    Scripta Materialia, 2014
    Co-Authors: Inchul Choi, Terence G. Langdon, M Kawasaki, Jaeil Jang
    Abstract:

    This study explores the evolution of plasticity, strain-rate sensitivity and the underlying Deformation Mechanism of a Zn–22% Al eutectoid alloy during high-pressure torsion processing. The experiments reveal an optimal torsional straining condition for achieving the largest plasticity; beyond this condition the strain-rate sensitivity decreases and activation volume increases. The results are discussed in terms of changes in the microstructure and the underlying Deformation Mechanism.

  • The many facets of Deformation Mechanism mapping and the application to nanostructured materials
    Journal of Materials Research, 2013
    Co-Authors: Megumi Kawasaki, Terence G. Langdon
    Abstract:

    Deformation Mechanism maps are well established in the field of high temperature creep for materials having conventional coarse grain sizes but they are almost unknown within the field of nanostructured materials. This paper summarizes the background to Deformation Mechanism mapping, presents simplified examples that may be used to easily construct appropriate maps for any selected condition, demonstrates the potential extension of this approach to other areas such as creep fracture, and then considers the potential limitations associated with using the same approach to predict the Deformation Mechanisms in true nanostructured materials. Two representative Deformation Mechanism maps are shown for an ultrafine-grained alloy processed either by equal-channel angular pressing or by high-pressure torsion.

  • Using Deformation Mechanism maps to depict flow processes in superplastic ultrafine-grained materials
    Journal of Materials Science, 2012
    Co-Authors: Megumi Kawasaki, Terence G. Langdon
    Abstract:

    Deformation Mechanism maps are a very useful tool for displaying Deformation Mechanisms as a function of the three fundamental parameters of high temperature flow: the applied stress, the testing temperature and the grain size of the material. These maps are used extensively in the field of high temperature creep but there has been very little use with ultrafine-grained (UFG) metals. This article reviews the principles of Deformation Mechanism maps, presents examples of maps for some representative metals processed by equal-channel angular pressing or high-pressure torsion and then describes a simple procedure for constructing maps for UFG materials.

Akhtar S Khan - One of the best experts on this subject based on the ideXlab platform.

  • a Deformation Mechanism based crystal plasticity model of ultrafine grained nanocrystalline fcc polycrystals
    International Journal of Plasticity, 2016
    Co-Authors: Akhtar S Khan
    Abstract:

    Abstract A new crystal plasticity model based on the Deformation Mechanism for ultrafine-grained/nanocrystalline face-centered cubic (FCC) metals was developed. The Deformation Mechanism was that dislocations glide from grain boundary to grain boundary (GB). Constitutive equations on the slip system level were developed based on dislocation glide and all stages of dislocation activities were considered especially their interactions with GB. An Arrhenius type rate equation was established based on the thermally activated depinning of dislocations from GB obstacles. The new constitutive equations were incorporated into a 3D crystal plasticity formulation, and this crystal plasticity model was implemented into a UMAT subroutine of the ABAQUS finite element program. The uniaxial Deformation responses of the two ufg/nc materials were simulated. Crystal plasticity finite element method (CPFEM) simulations gave flow stress predictions that were very close to the experimental results. The dislocation Mechanism-based crystal plasticity UMAT is ready to be used for more advanced simulation studies.

  • A Deformation Mechanism based crystal plasticity model of ultrafine-grained/nanocrystalline FCC polycrystals
    International Journal of Plasticity, 2016
    Co-Authors: Akhtar S Khan, Jian Liu
    Abstract:

    Abstract A new crystal plasticity model based on the Deformation Mechanism for ultrafine-grained/nanocrystalline face-centered cubic (FCC) metals was developed. The Deformation Mechanism was that dislocations glide from grain boundary to grain boundary (GB). Constitutive equations on the slip system level were developed based on dislocation glide and all stages of dislocation activities were considered especially their interactions with GB. An Arrhenius type rate equation was established based on the thermally activated depinning of dislocations from GB obstacles. The new constitutive equations were incorporated into a 3D crystal plasticity formulation, and this crystal plasticity model was implemented into a UMAT subroutine of the ABAQUS finite element program. The uniaxial Deformation responses of the two ufg/nc materials were simulated. Crystal plasticity finite element method (CPFEM) simulations gave flow stress predictions that were very close to the experimental results. The dislocation Mechanism-based crystal plasticity UMAT is ready to be used for more advanced simulation studies.

Zhiwei Shan - One of the best experts on this subject based on the ideXlab platform.

  • Deformation Mechanism maps for sub micron sized aluminum
    Acta Materialia, 2020
    Co-Authors: Degang Xie, Rongrong Zhang, Zhiyu Nie, Zhiwei Shan
    Abstract:

    Abstract Plastic Deformation of sub-μm sized metals at different temperatures is influenced by factors absent in their bulk counterparts, including surface diffusion assisted softening and mechanical/thermal annealing-induced hardening. The test temperature and sample size therefore strongly affect the mechanical behavior, necessitating the construction of new Deformation Mechanism maps (DMM). Here, based on results from in situ quantitative compression tests on micro-pillars at various sizes and temperatures ranging up to 400°C, we have constructed DMMs for single-crystalline sub-micron-scale aluminum, consisting of elasticity, diffusive plasticity, and displacive plasticity regimes. In the sample size-stress DMM (for a fixed temperature), a “strongest size” is found at the triple junction of three regimes, above which “smaller is stronger”, below which “smaller is weaker”. In the diffusive plasticity regime, Deformation is localized within the top pillar volume demarcated by a moving front interface, which is likely a newly formed grain boundary, that is impenetrable to impinging dislocations below a critical stress of ∼1 GPa.

  • visualizing size dependent Deformation Mechanism transition in sn
    Scientific Reports, 2013
    Co-Authors: Lin Tian, Jun Sun, Zhiwei Shan
    Abstract:

    Displacive Deformation via dislocation slip and Deformation twinning usually plays a dominant role in the plasticity of crystalline solids at room temperature. Here we report in situ quantitative transmission electron microscope Deformation tests of single crystal Sn samples. We found that when the sample size was reduced from 450 nm down to 130 nm, diffusional Deformation replaces displacive plasticity as the dominant Deformation Mechanism at room temperature. At the same time, the strength-size relationship changed from ‘‘smaller is stronger’’ to ‘‘smaller is much weaker’’. The effective surface diffusivity calculated based on our experimental data matches well with that reported in literature for boundary diffusion. The observed change in the Deformation mode arises from the sample size-dependent competition between the Hall-Petch-like strengthening of displacive processes and Coble diffusion softening processes. Our findings have important implications for the stability and reliability of nanoscale devices such as metallic nanogaps.

Kenji Higashi - One of the best experts on this subject based on the ideXlab platform.

  • superplastic Deformation Mechanism in powder metallurgy magnesium alloys and composites
    Acta Materialia, 2001
    Co-Authors: Hiroyuki Watanabe, Toshiji Mukai, Mamoru Mabuchi, Kenji Higashi
    Abstract:

    Abstract The parametric dependencies for superplastic flow in powder metallurgy (PM) magnesium alloys and composites were characterized so as to elucidate the Deformation Mechanism. The Mechanism was proposed to be slip accommodated grain boundary sliding. However, the PM alloys and composites were strengthened at low temperatures below ∼550K. This was different from the case in ingot metallurgy (IM) magnesium alloys, that behaved identically over a wide range of temperatures. The critical strain rate, below which the effect of intragranular particle is lost, was developed by considering the dislocation–particle interaction during slip accommodation process. It was suggested that the diffusional relaxation around the intragranular oxide particles was not completed during the slip accommodation process at low temperatures, and this caused the dislocation pile-up at the intragranular particles. It was expected that the dislocation pile-up at the intragranular particles would contribute to the strengthening at low temperatures in PM alloys and PM composites.

  • Deformation Mechanism in a coarse grained mg al zn alloy at elevated temperatures
    International Journal of Plasticity, 2001
    Co-Authors: Hiroyuki Watanabe, H Tsutsui, Toshiji Mukai, Masahide Kohzu, Shigenori Tanabe, Kenji Higashi
    Abstract:

    Deformation behavior of a coarse-grained AZ31 magnesium alloy was investigated at elevated temperatures using commercial rolled sheet. The as-received material had equiaxed grains with an average grain size of 130 μm. The tensile tests revealed that the material exhibited high ductility of 196% at 648 K and 3×10−5 s−1. Stress exponent, grain size exponent and activation energy were characterized to clarify the Deformation Mechanism. It was suggested from the data analysis that the high ductility was attributed to the Deformation Mechanism of glide-controlled dislocation creep. In addition, constitutive equation was developed for the present alloy.

Huan Chang Lin - One of the best experts on this subject based on the ideXlab platform.

  • process design based on the Deformation Mechanism for the non isothermal forging of ti 6al 4v alloy
    Journal of Materials Processing Technology, 1998
    Co-Authors: Rongshean Lee, Huan Chang Lin
    Abstract:

    Abstract Non-isothermal forging has been widely employed in the metalworking industry. Although the die-chilling effect is very significant in the non-isothermal forging process, the process parameters of time and temperature are difficult to measure and control during non-isothermal forging. To cope with this problem, this study employs the thermal-coupled finite element method to examine and to establish the relationship between the process parameters and the Deformation behaviour, then deriving useful design rules. The detailed process model based on experimental conditions, and the flow stress model constructed by the localized linear fitting and interpolation method, were used in the finite element analysis. Consequently, the simulation of the non-isothermal forging of Ti–6Al–4V was performed, the predicted results agreeing well with those from experiment. Due to the large temperature gradient, the mode of Deformation in non-isothermal forging is different from that in isothermal Deformation. Therefore, a Deformation Mechanism for non-isothermal forging was proposed in this paper to explain the Deformation behaviour. Hence, the Deformation Mechanism governing the metal flow of non-isothermal forging can provide guidelines for forging die design and process design.