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Title: Strain Hardening and Long-Range Internal Stress in the Localized Deformation of Irradiated Polycrystalline Metals

Abstract

Low-temperature irradiation can significantly harden metallic materials and often results in microscopic strain localization such as dislocation channeling during deformation. In true stress-true strain analyses, however, the strain localization does not significantly affect macroscopic strain-hardening behavior. It was attempted to explain the strain-hardening behavior during strain localization in terms of long-range back stresses. In theoretical modeling the long-range back stress was formulated as a function of the number of residual pileup dislocations at a grain boundary and the number of localized bands formed in a grain. The strain-hardening rates in channel deformation were calculated for ten face-centered cubic (fcc) and body-centered cubic (bcc) metals. A few residual dislocations in each channel could account for the strain-hardening rates as high as those for uniform deformation. It was also shown that the strain-hardening behavior predicted by the long-range back stress model resembled the empirical strain-hardening behaviors, which result from both localized and non-localized deformations. The predicted plastic instability stress was comparable to the tensile test data.

Authors:
 [1];  [1]
  1. ORNL
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); High Flux Isotope Reactor
Sponsoring Org.:
Work for Others (WFO)
OSTI Identifier:
1003392
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Nuclear Materials; Journal Volume: 354; Journal Issue: 1-3
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; DISLOCATIONS; IRRADIATION; STRAIN HARDENING; STRESSES; MATHEMATICAL MODELS; METALS; BCC LATTICES; FCC LATTICES

Citation Formats

Byun, Thak Sang, and Hashimoto, Naoyuki. Strain Hardening and Long-Range Internal Stress in the Localized Deformation of Irradiated Polycrystalline Metals. United States: N. p., 2006. Web. doi:10.1016/j.jnucmat.2006.02.099.
Byun, Thak Sang, & Hashimoto, Naoyuki. Strain Hardening and Long-Range Internal Stress in the Localized Deformation of Irradiated Polycrystalline Metals. United States. doi:10.1016/j.jnucmat.2006.02.099.
Byun, Thak Sang, and Hashimoto, Naoyuki. Sun . "Strain Hardening and Long-Range Internal Stress in the Localized Deformation of Irradiated Polycrystalline Metals". United States. doi:10.1016/j.jnucmat.2006.02.099.
@article{osti_1003392,
title = {Strain Hardening and Long-Range Internal Stress in the Localized Deformation of Irradiated Polycrystalline Metals},
author = {Byun, Thak Sang and Hashimoto, Naoyuki},
abstractNote = {Low-temperature irradiation can significantly harden metallic materials and often results in microscopic strain localization such as dislocation channeling during deformation. In true stress-true strain analyses, however, the strain localization does not significantly affect macroscopic strain-hardening behavior. It was attempted to explain the strain-hardening behavior during strain localization in terms of long-range back stresses. In theoretical modeling the long-range back stress was formulated as a function of the number of residual pileup dislocations at a grain boundary and the number of localized bands formed in a grain. The strain-hardening rates in channel deformation were calculated for ten face-centered cubic (fcc) and body-centered cubic (bcc) metals. A few residual dislocations in each channel could account for the strain-hardening rates as high as those for uniform deformation. It was also shown that the strain-hardening behavior predicted by the long-range back stress model resembled the empirical strain-hardening behaviors, which result from both localized and non-localized deformations. The predicted plastic instability stress was comparable to the tensile test data.},
doi = {10.1016/j.jnucmat.2006.02.099},
journal = {Journal of Nuclear Materials},
number = 1-3,
volume = 354,
place = {United States},
year = {Sun Jan 01 00:00:00 EST 2006},
month = {Sun Jan 01 00:00:00 EST 2006}
}
  • Effects of irradiation at temperatures 200oC on tensile stress parameters are analyzed for dozens of bcc, fcc, and hcp pure metals and alloys, focusing on irradiation hardening, strain hardening, and relationships between the true stress parameters. Similar irradiation-hardening rates are observed for all the metals irrespective of crystal type; typically, the irradiation-hardening rates are large, in the range 100 - 1000 GPa/dpa, at the lowest dose of <0.0001 dpa and decrease with dose to a few tens of MPa/dpa or less at about 10 dpa. However, average irradiation-hardening rates over the dose range of 0 dpa − (the dose tomore » plastic instability at yield) are considerably lower for stainless steels due to their high uniform ductility. It is shown that whereas low temperature irradiation increases the yield stress, it does not significantly change the strain-hardening rate of metallic materials; it decreases the fracture stress only when non-ductile failure occurs. Such dose independence in strain hardening behavior results in strong linear relationships between the true stress parameters. Average ratios of plastic instability stress to unirradiated yield stress are about 1.4, 3.9, and 1.3 for bcc metals (and precipitation hardened IN718 alloy), annealed fcc metals (and pure Zr), and Zr-4 alloy, respectively. Ratios of fracture stress to plastic instability stress are calculated to be 2.2, 1.7, and 2.1, respectively. Comparison of these values confirms that the annealed fcc metals and other soft metals have larger uniform ductility but smaller necking ductility when compared to other materials.« less
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  • Long-range internal stresses in dislocation cell and subgrain structures were investigated experimentally. The transition of the dislocation structure from cells to subgrains was achieved by deforming copper polycrystals in compression creep tests at constant stress normalized by the shear modulus in the temperature range from 298 K to 633 K. The long-range internal stresses were investigated by two methods. The first one was the evaluation of characteristically asymmetric X-ray line profiles. The internal stresses are the result of the analysis of the X-ray line profiles. The second one was the measurement of local lattice parameters. The results obtained from bothmore » methods show that long-range internal stresses of the same type exist in the cell as well as in the subgrain structures.« less
  • Synchrotron X-ray microbeam diffraction was used to measure the full elastic long range internal strain and stress tensors of low dislocation density regions within the submicrometer grain/subgrain structure of equal-channel angular pressed (ECAP) aluminum alloy AA1050 after 1, 2, and 8 passes using route B C. This is the first time that full tensors were measured in plastically deformed metals at this length scale. The maximum (most tensile or least compressive) principal elastic strain directions for the unloaded 1 pass sample for the grain/subgrain interiors align well with the pressing direction, and are more random for the 2 and 8more » pass samples. The measurements reported here indicate that the local stresses and strains become increasingly isotropic (homogenized) with increasing ECAP passes using route BC. The average maximum (in magnitude) LRISs are -0.43 σ a for 1 pass, -0.44 σ a for 2 pass, and 0.14 σ a for the 8 pass sample. Furthermore, these LRISs are larger than those reported previously because those earlier measurements were unable to measure the full stress tensor. Significantly, the measured stresses are inconsistent with the two-component composite model.« less