Non-glide effects and dislocation core fields in BCC metals

AbstractA hallmark of low-temperature plasticity in body-centered cubic (BCC) metals is its departure from Schmid’s law. One aspect is that non-glide stresses, which do not produce any driving force on the dislocations, may affect the yield stress. We show here that this effect is due to a variation of the relaxation volume of the $$1/2\langle 111\rangle$$1∕2⟨111⟩ screw dislocations during glide. We predict quantitatively non-glide effects by modeling the dislocation core as an Eshelby inclusion, which couples elastically to the applied stress. This model explains the physical origin of the generalized yield criterion classically used to include non-Schmid effects in constitutive models of BCC plasticity. We use first-principles calculations to properly account for dislocation cores and use tungsten as a reference BCC metal. However, the methodology developed here applies to other BCC metals, other energy models and other solids showing non-glide effects.

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First-Principles Calculations of Oxygen-Dislocation Interaction in Magnesium

Materials ◽

10.3390/ma13010116 ◽

2019 ◽

Vol 13 (1) ◽

pp. 116

Author(s):

Chao Fang ◽

Jing Zhang ◽

Ying Huang ◽

Jianhao Chen

Keyword(s):

Screw Dislocation ◽

First Principles ◽

Dislocation Core ◽

Prismatic Slip ◽

Interstitial Oxygen ◽

First Principles Calculations ◽

Dislocation Interaction ◽

Dislocation Glide ◽

Deformation Behaviors ◽

Oxygen Atoms

The interaction between interstitial oxygen atoms and <a>-type screw dislocations was investigated via first-principles calculations to elucidate the effect of oxygen solutes on the deformation behaviors of Mg. The results show that repulsive interactions exist between basal screw dislocation cores and oxygen atoms, which would enable the full basal dislocation to bypass the oxygen atoms in the dislocation glide plane through the cross-slip process. This repulsion also increases the resistance to the motion of dissociated basal dislocations. Moreover, the energy of prismatic <a>-type screw dislocation cores is reduced by the presence of oxygen, which would stabilize the screw dislocation core on the prismatic plane, accordingly facilitating the prismatic slip. This information can complement the fundamental knowledge of alloying Mg using interstitial solutes.

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First-principles calculations of vacancy–solute element interactions in body-centered cubic iron

Acta Materialia ◽

10.1016/j.actamat.2009.08.020 ◽

2009 ◽

Vol 57 (20) ◽

pp. 5947-5955 ◽

Cited By ~ 94

Author(s):

Toshiharu Ohnuma ◽

Naoki Soneda ◽

Misako Iwasawa

Keyword(s):

First Principles ◽

First Principles Calculations ◽

Body Centered Cubic ◽

Solute Element ◽

Element Interactions

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Origin of dramatic oxygen solute strengthening effect in titanium

Science ◽

10.1126/science.1260485 ◽

2015 ◽

Vol 347 (6222) ◽

pp. 635-639 ◽

Cited By ~ 135

Author(s):

Qian Yu ◽

Liang Qi ◽

Tomohito Tsuru ◽

Rachel Traylor ◽

David Rugg ◽

...

Keyword(s):

First Principles ◽

Dislocation Core ◽

Strengthening Effect ◽

First Principles Calculations ◽

Screw Dislocations ◽

Elastic Fields ◽

Transmission Electron ◽

Short Range Repulsion ◽

Solute Atoms ◽

Solute Strengthening

Structural alloys are often strengthened through the addition of solute atoms. However, given that solute atoms interact weakly with the elastic fields of screw dislocations, it has long been accepted that solution hardening is only marginally effective in materials with mobile screw dislocations. By using transmission electron microscopy and nanomechanical characterization, we report that the intense hardening effect of dilute oxygen solutes in pure α-Ti is due to the interaction between oxygen and the core of screw dislocations that mainly glide on prismatic planes. First-principles calculations reveal that distortion of the interstitial sites at the screw dislocation core creates a very strong but short-range repulsion for oxygen that is consistent with experimental observations. These results establish a highly effective mechanism for strengthening by interstitial solutes.

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Partial Dislocations under Forward Bias in SiC

Materials Science Forum ◽

10.4028/www.scientific.net/msf.556-557.279 ◽

2007 ◽

Vol 556-557 ◽

pp. 279-282 ◽

Cited By ~ 2

Author(s):

G. Savini ◽

A.A. El Barbary ◽

M.I. Heggie ◽

Sven Öberg

Keyword(s):

First Principles ◽

Dislocation Line ◽

Forward Bias ◽

Dislocation Core ◽

First Principles Calculations ◽

Dangling Bond ◽

Free Energies ◽

Electron Hole ◽

Partial Dislocations ◽

Conduction Bands

First-principles calculations are used to investigate the partial dislocations in 4H-SiC. We have shown that the Peierls barriers are strongly dependent on the dislocation core structures. Our results have revealed that the asymmetric reconstruction does not possess midgap states while the symmetric reconstructions, characterized by dangling bond on like atoms along the dislocation line, are always electrically active. We suggested that under forward bias, the free energies of the symmetric reconstructions are dynamically lowered by continuous electron-hole transitions between the respective deep levels and valence/conduction bands.

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Screw dislocation core structure in the paramagnetic state of bcc iron from first-principles calculations

Physical Review B ◽

10.1103/physrevb.102.094420 ◽

2020 ◽

Vol 102 (9) ◽

Author(s):

Luis Casillas-Trujillo ◽

Davide Gambino ◽

Lisa Ventelon ◽

Björn Alling

Keyword(s):

Screw Dislocation ◽

First Principles ◽

Dislocation Core ◽

Paramagnetic State ◽

Core Structure ◽

First Principles Calculations ◽

Bcc Iron ◽

Dislocation Core Structure

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Strong anisotropic nodal lines in the TiBe family

Physical Chemistry Chemical Physics ◽

10.1039/c9cp00508k ◽

2019 ◽

Vol 21 (16) ◽

pp. 8402-8407 ◽

Cited By ~ 7

Author(s):

Z. C. Zou ◽

P. Zhou ◽

Z. S. Ma ◽

L. Z. Sun

Keyword(s):

First Principles ◽

Energy Band ◽

Model Analysis ◽

The Body ◽

Low Energy ◽

First Principles Calculations ◽

Body Centered Cubic ◽

Band Structures ◽

Nodal Lines

Using first-principles calculations and k·p model analysis, we find that Dirac nodal lines (DNLs) exist in low energy band structures of real materials of the body-centered cubic TiBe family.

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The Effect of Surface Oxide Films on the Mechanical Behavior of NiAl

MRS Proceedings ◽

10.1557/proc-39-319 ◽

1984 ◽

Vol 39 ◽

Author(s):

R. D. Noebe ◽

R. Gibala

Keyword(s):

Mechanical Behavior ◽

Surface Film ◽

Dislocation Core ◽

The Body ◽

Surface Films ◽

Intermetallic Alloys ◽

Body Centered Cubic ◽

Cubic Metals ◽

Bcc Metals ◽

Ordered Intermetallic

ABSTRACTThin surface films have been shown to enhance the ductility and decrease the flow stress of several body-centered cubic metals at temperatures T < 0.2 Tm. The origin of this effect lies in the large difference in the intrinsic mobilities of edge and screw dislocations in body-centered cubic crystals. B2 ordered intermetallic alloys, although simple cubic in structure, are based on the body-centered cubic structure and have dislocation core structures, dislocation mobilities and temperature and orientation dependent deformation qualitatively similar to that of bcc metals. This investigation was initiated to examine possible effects of surface films on the mechanical behavior of B2 ordered intermetallic alloys, using oxidized NiAl as the initial material for investigation. Experiments were performed on an impure non-stoichiometric (47.1 at.% Al) single crystal material with an axial orientation near [123]. Surface film softening was observed at room temperature in compression at a strain rate of 2 x 10-4 s-1. Flow stresses of the oxide coated crystals were as much as 20% lower than those of identically prepared uncoated crystals. The strains to fracture of coated specimens were larger than those of uncoated specimens and in a few instances the ductility enhancement was as much as four times. Of the several oxides examined, the largest softening effects were found for a thermally deposited delta-A1203 film formed at 1000 °C for 1 hour. The current results for NiAl are compared to results previously obtained for bcc metals. Experiments which could further enhance the film softening effects observed in B2 ordered intermetallic alloys are suggested.

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Alloy Design and Mechanical Properties: First-principles Calculations of Dislocation Core

Materia Japan ◽

10.2320/materia.56.5 ◽

2017 ◽

Vol 56 (1) ◽

pp. 5-13

Author(s):

Tomohito Tsuru

Keyword(s):

Mechanical Properties ◽

First Principles ◽

Dislocation Core ◽

Alloy Design ◽

First Principles Calculations

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Theoretical Study of Inter-Planer Ordering of Mg-Based LPSO Structures

Solid State Phenomena ◽

10.4028/www.scientific.net/ssp.258.41 ◽

2016 ◽

Vol 258 ◽

pp. 41-44 ◽

Cited By ~ 1

Author(s):

Daisuke Matsunaka ◽

Yoji Shibutani

Keyword(s):

First Principles ◽

Formation Energy ◽

Theoretical Study ◽

Mass Change ◽

Chain Model ◽

First Principles Calculations ◽

Physical Origin ◽

Lpso Structure ◽

Solute Atoms ◽

Periodic Arrangement

To study the physical origin of the periodic arrangement of the quadrople solute-enriched layers in Mg-based LPSO structures, we carry out first-principles calculations of the formation energy of the L12 cluster and investigate effects of phonon on the inter-planer ordering of the solute-enriched layers using the 1-dimensional chain model with mass change. The formation energy of the L12 cluster increases as the period of the LPSO structure decreases. Thus, it is found that the electron-mediated interaction is short-range repulsive. On the other hand, in the case of considerably heavy mass change, the ordering of the mass changes is stabilized by phonons and the energy gain increases with the concentration of the mass changes, i.e., the short LPSO period is favorable. A promising mechanism of the inter-planer ordering of the LPSO structures is the phonon-mediated interaction of the quadrople layers where heavy solute atoms are enriched as the L12 clusters at SFs.

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