Dislocation motion, constriction and cross-slip in fcc metals

ABSTRACTWe present evidence for the operation on reconstructed Au(001) of a novel mechanism, involving dislocation motion, which is much more efficient than surface diffusion to redistribute mass around nanoindentations. Cross-slip of individual dislocations generated around the indentation point, with a screw component perpendicular to the surface, is shown to be responsible for the generation of multiple-storied, crystallographically-oriented terraces around the nanoindentation points. We also show that standard dislocation theory can be used to quantitatively describe the characteristics of the dislocations involved in the different processes around the nanoindentation.

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Stochastic Dislocation Dynamics under Creep Conditions in Metals

MRS Proceedings ◽

10.1557/proc-731-w1.7 ◽

2002 ◽

Vol 731 ◽

Author(s):

Masato Hiratani ◽

Hussein M. Zbib

Keyword(s):

Thermal Fluctuation ◽

Dislocation Motion ◽

Cross Slip ◽

Dislocation Dynamics ◽

Atomistic Simulations ◽

Thermal Processes ◽

New Model ◽

Slip Mechanism ◽

Fcc Metals ◽

Thermally Activated

AbstractA stochastic model is proposed to study dislocation dynamics in metallic single crystals. A Langevin type thermal fluctuation is taken into account for the model to maintain thermal equilibrium. This approach works as Brownian motion of segmental dislocations. Additionally, a new model for implementing the cross slip mechanism in FCC metals is developed based on results obtained by atomistic simulations. This new model is capable of simulating realistic thermal processes such as thermally activated dislocation motion during easy glide or cross slip during cold working of metals.

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A dipole model for the cross-slip of screw dislocations in fcc metals

Philosophical Magazine A ◽

10.1080/01418610210130976 ◽

2002 ◽

Vol 82 (9) ◽

pp. 1691-1711 ◽

Cited By ~ 2

Author(s):

L. M. Brown

Keyword(s):

Cross Slip ◽

Dipole Model ◽

Screw Dislocations ◽

Fcc Metals ◽

The Cross

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On the Stress Anomaly of γ-TiAl

MRS Proceedings ◽

10.1557/proc-646-n7.10.1 ◽

2000 ◽

Vol 646 ◽

Author(s):

Marc C. Fivel ◽

Francois Louchet ◽

Bernard Viguier ◽

Marc Verdier

Keyword(s):

Dislocation Motion ◽

Cross Slip ◽

Screw Dislocations ◽

Mesoscopic Simulation ◽

Temperature Range ◽

Ordinary Dislocation ◽

Dislocation Behaviour

ABSTRACTA 3D mesoscopic simulation of dislocation behaviour is adapted to the case of γ-TiAl. It shows that, in the temperature range of the stress anomaly, ordinary dislocation motion essentially proceeds through a series of pinning and unzipping processes on screw dislocations. Pinning points are cross-slip generated jogs, whose density increases with temperature. Unzipping of cusps restores the screw character of the dislocation. The balance between pinning and unzipping becomes increasingly difficult as temperature raises, and results in dislocation exhaustion. All these features agree with the so-called “Local Pinning Unzipping” mechanism.

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Dislocation Cross-Slip in Nanocrystalline fcc Metals

Physical Review Letters ◽

10.1103/physrevlett.100.235501 ◽

2008 ◽

Vol 100 (23) ◽

Cited By ~ 52

Author(s):

E. Bitzek ◽

C. Brandl ◽

P. M. Derlet ◽

H. Van Swygenhoven

Keyword(s):

Cross Slip ◽

Fcc Metals

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The Role of Stacking Fault Energy on the Indentation Size Effect of FCC Pure Metals and Alloys

MRS Proceedings ◽

10.1557/opl.2012.232 ◽

2012 ◽

Vol 1424 ◽

Cited By ~ 1

Author(s):

D.E. Stegall ◽

M.A. Mamun ◽

A.A. Elmustafa

Keyword(s):

Size Effect ◽

Indentation Size Effect ◽

Stacking Fault ◽

Cross Slip ◽

Indentation Size ◽

Fcc Metals ◽

Partial Dislocations ◽

Dislocation Movement ◽

Pure Metals ◽

Interfacial Characteristic

ABSTRACTWe investigated the effect of stacking fault free energy (SFE), on the magnitude of the indentation size effect (ISE) of several pure FCC metals using nanoindentation. The metals chosen were 99.999% Aluminum, 99.95% Nickel, 99.95% Silver, and 70/30 Copper Zinc (α-brass). Aluminum has a high SFE of about 200 mJ/ m2, whereas α -brass has a low SFE of less than 10 mJ/ m2. Nickel and Silver have intermediate SFE of about 128 mJ/ m2 and 22 mJ/m2 respectively. The SFE is an important interfacial characteristic and plays a significant role in the deformation of FCC metals due to its influence on dislocation movement and morphology. The SFE is a measure of the distance between partial dislocations and has a direct impact on the ability of dislocations to cross slip during plastic deformation. The lower the SFE the larger the separation between partial dislocations and thus cross slip and dynamic recovery are inhibited. The SFE impacts pure metals differently from alloys. It was discovered that the characteristic ISE behavior for the pure metals was different when compared to the α-brass which is an alloy. Several additional alloys were chosen for comparison including 7075 Aluminum and 70/30 Nickel Copper.

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Are rate sensitivity and strength effected by cross-slip in nano-twinned fcc metals

Scripta Materialia ◽

10.1016/j.scriptamat.2007.06.066 ◽

2008 ◽

Vol 58 (5) ◽

pp. 389-392 ◽

Cited By ~ 38

Author(s):

Robert J Asaro ◽

Yashashree Kulkarni

Keyword(s):

Rate Sensitivity ◽

Cross Slip ◽

Fcc Metals

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Simulation of Dislocation Dynamics in Ni3Al: A Study of Velocity Autocorrelations

MRS Proceedings ◽

10.1557/proc-578-143 ◽

1999 ◽

Vol 578 ◽

Author(s):

C. K. Erdonmez ◽

D. C. Chrzan

Keyword(s):

Yield Strength ◽

Applied Stress ◽

Critical Stress ◽

Threshold Stress ◽

Dislocation Motion ◽

Cross Slip ◽

Dislocation Dynamics ◽

Thermally Activated ◽

Simple Rules ◽

Isotropic Elasticity

AbstractThe yield strength anomaly in some L12 compounds has been linked to the thermally assisted cross slip of screw superdislocations. This work continues earlier efforts to understand the yield strength anomaly in L12 alloys using computer simulations of dislocation motion. Dislocations are modelled within isotropic elasticity theory, and simple rules are used to model the cross-slip process in the two dimensional geometry of the simulation. The velocity of a single dislocation in Ni3Al is studied as a function of the applied stress. The observed velocities vary nonlinearly with the applied stress. Further, dislocations are observed to become immobile for small applied loads. At high stresses, the dislocations are observed to advance relatively unhindered by the thermally activated cross slip process. Fluctuations in the velocity of the dislocations are studied, and their autocorrelation function shows an increased correlation time near a threshold stress. This threshold stress is identified with the critical stress proposed in earlier works.

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