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Title: Strengthening and microstructure modification associated with moving twin boundaries in hcp metals

Abstract

The interaction of a moving {1012} twin boundary (TB) with clusters of self-interstitial atoms and vacancies, containing up to 35 point defects, has been studied by atomic computer simulation in a model crystal of hcp Zr. Conservative movement of the boundary has been achieved by glide of twinning dislocations under applied shear stress. Several reactions were observed, the result depending on cluster orientation and location relative to the glide plane of the twinning dislocation, i.e. tension or compression region. They included 1) restriction of TB mobility; 2) change of cluster orientation and shape; 3) glissile cluster drag by the TB without contact; and 4) total or partial absorption of a cluster by the TB and cluster drag, together with simultaneous glide along the TB. It is concluded that the applied shear stress for motion of TBs is raised by interaction with point defect clusters. Furthermore, moving TBs act as defect sinks or recombination centres and provide a means for removing defects from regions of radiation damage.

Authors:
 [1];  [2];  [3]
  1. Universitat Politecnica de Catalunya
  2. University of Liverpool
  3. ORNL
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
958785
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Journal Article
Resource Relation:
Journal Name: Philosophical Magazine Letters; Journal Volume: 87; Journal Issue: 7
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ABSORPTION; ATOMS; COMPRESSION; COMPUTERIZED SIMULATION; DEFECTS; DISLOCATIONS; MICROSTRUCTURE; MODIFICATIONS; ORIENTATION; POINT DEFECTS; RADIATIONS; RECOMBINATION; SHAPE; SHEAR; TWINNING; VACANCIES; twin bondaries; moving interfaces; radiation defects

Citation Formats

Serra, Anna, Bacon, David J, and Osetskiy, Yury N. Strengthening and microstructure modification associated with moving twin boundaries in hcp metals. United States: N. p., 2007. Web. doi:10.1080/09500830701244812.
Serra, Anna, Bacon, David J, & Osetskiy, Yury N. Strengthening and microstructure modification associated with moving twin boundaries in hcp metals. United States. doi:10.1080/09500830701244812.
Serra, Anna, Bacon, David J, and Osetskiy, Yury N. Mon . "Strengthening and microstructure modification associated with moving twin boundaries in hcp metals". United States. doi:10.1080/09500830701244812.
@article{osti_958785,
title = {Strengthening and microstructure modification associated with moving twin boundaries in hcp metals},
author = {Serra, Anna and Bacon, David J and Osetskiy, Yury N},
abstractNote = {The interaction of a moving {1012} twin boundary (TB) with clusters of self-interstitial atoms and vacancies, containing up to 35 point defects, has been studied by atomic computer simulation in a model crystal of hcp Zr. Conservative movement of the boundary has been achieved by glide of twinning dislocations under applied shear stress. Several reactions were observed, the result depending on cluster orientation and location relative to the glide plane of the twinning dislocation, i.e. tension or compression region. They included 1) restriction of TB mobility; 2) change of cluster orientation and shape; 3) glissile cluster drag by the TB without contact; and 4) total or partial absorption of a cluster by the TB and cluster drag, together with simultaneous glide along the TB. It is concluded that the applied shear stress for motion of TBs is raised by interaction with point defect clusters. Furthermore, moving TBs act as defect sinks or recombination centres and provide a means for removing defects from regions of radiation damage.},
doi = {10.1080/09500830701244812},
journal = {Philosophical Magazine Letters},
number = 7,
volume = 87,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}
  • We develop the monomer, a molecular statics technique for the search of transition states under conditions of relatively complex atomistic environments. As its counterpart from the literature, the dimer, our method is based on forces evaluation alone and is able to find the saddle configuration without previous knowledge of the equilibrium state across the saddle; at variance with it, the needed local curvature is determined with just one force evaluation per iteration step. The method is here applied to the location of saddle configurations relevant to the migration of vacancies and self-interstitials in the (1121) and (1122) twin boundaries ofmore » {alpha}-Zr modeled with an embedded atom type interatomic potential. Besides the fundamental interest of studying migration in these environments of reduced symmetry and dimensionality, we aim at a better understanding of grain boundaries as agents contributing to the mechanical deformation under irradiation conditions. Whereas vacancies have already been studied in the same boundaries employing a different methodology, self-interstitial results are new. For comparison purposes and completeness however, some results relating to vacancies are also included. Our main findings relate to the prediction of very low interstitial migration energies that radically change the anisotropy of bulk migration. This behavior may be associated, though not necessarily, with spatially extended configurations. The results suggest that the picture of grain boundaries as essentially perfect sinks, common to models of irradiation creep and growth, may need revision.« less
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  • We have performed total-energy electronic structure calculations to examine competing structures for the twin boundary, which can form under tensile stress along the c axis. The twin boundary structures are significantly different, most notably in their symmetry. These calculations show that, for all materials studied, the different structures have nearly the same energy, in agreement with calculations from empirical potentials. This result is surprising, given the difference in the structures, and the fact that previous first-principles calculations of the energies of compression twin boundaries have shown significant differences from empirical potentials.
  • Herein, we use first principles calculations to study the energy of the (1121) twin boundary in Zr, Zn, Mg, Ti, and Be. This boundary is important for understanding the microyielding and damping of hexagonal close-packed metals. The (1121) twin boundary is unique in that it is composed of--and can form by the glide of--basal dislocations nucleating at every c lattice parameter. The effect of the number of atoms between boundaries on the boundary energy, and the resulting lattice strains of the relaxed structures are quantified. It is shown that the energies obtained converge within 32-64 atoms/supercell. The structures with amore » higher second-order elastic constant term, c{sub 44}, also have higher boundary energies. It is further shown that the critical resolved shear stresses of the basal dislocations at 0 K, which make up the (1121) twin, are so low as to be below the threshold of the first principles calculations.« less
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