On kinked screw dislocations in the b.c.c. lattice—I. The structure and peierls stress of isolated kinks
TL;DR: In this paper, the core structures and lattice friction stresses of single kinks on a screw dislocation in the b.c. lattice have been calculated by means of computer simulation.
About: This article is published in Acta Metallurgica.The article was published on 1983-10-01. It has received 69 citations till now. The article focuses on the topics: Peierls stress & Dislocation.
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TL;DR: In this article, the most important cross-slip models found in literature are reviewed and a critical comparison of different models is made including constriction energies and stress dependence, and the advantages and inherent weaknesses of the different approaches are discussed.
311 citations
TL;DR: In this article, the authors present molecular dynamics simulations of screw dislocation motion as a function of temperature and stress in order to extract mobility relations that describe the general dynamic behavior of screw dislocations in pure $\ensuremath{\alpha}$-Fe.
Abstract: The low-temperature plastic yield of $\ensuremath{\alpha}$-Fe single crystals is known to display a strong temperature dependence and to be controlled by the thermally activated motion of screw dislocations. In this paper, we present molecular dynamics simulations of $\frac{1}{2}\ensuremath{\langle}111\ensuremath{\rangle}$${112}$ screw dislocation motion as a function of temperature and stress in order to extract mobility relations that describe the general dynamic behavior of screw dislocations in pure $\ensuremath{\alpha}$-Fe. We find two dynamic regimes in the stress-velocity space governed by different mechanisms of motion. Consistent with experimental evidence, at low stresses and temperatures, the dislocations move by thermally activated nucleation and propagation of kink pairs. Then, at a critical stress, a temperature-dependent transition to a viscous linear regime is observed. Critical output from the simulations, such as threshold stresses and the stress dependence of the kink activation energy, are compared to experimental data and other atomistic works with generally very good agreement. Contrary to some experimental interpretations, we find that glide on ${112}$ planes is only apparent, as slip always occurs by elementary kink-pair nucleation/propagation events on ${110}$ planes. Additionally, a dislocation core transformation from compact to dissociated has been identified above room temperature, although its impact on the general mobility is seen to be limited. This and other observations expose the limitations of inferring or presuming dynamic behavior on the basis of only static calculations. We discuss the relevance and applicability of our results and provide a closed-form functional mobility law suitable for mesoscale computational techniques.
156 citations
01 Jan 2004
TL;DR: In this article, the atomic structure and interactions in the dislocation core and their effects on dislocation mobility from the standpoint of theoretical concepts, physical models and simulation studies, with due consideration of relevant experimental results.
Abstract: This chapter discusses the dislocation core effects on mobility. Its purpose is to discuss the atomic structure and interactions in the dislocation core and their effects on dislocation mobility from the standpoint of theoretical concepts, physical models and simulation studies, with due consideration of relevant experimental results. The major emphasis is placed on physical ideas and observations. In fact, technical details of modeling and experiments are only briefly mentioned and only where required for clarification of physics issues or for interpretation of results. The existence of glide and shuffle sets of dislocation positions in diamond cubic semiconductors introduces still more complexity with regard to the role of core mechanisms in dislocation motion. Plasticity behavior of BCC metals is controlled, to a large extent, by the motion of screw dislocations.
148 citations
TL;DR: The art of forming materials into technologically useful artifacts by manipulation of the dislocation substructure dates back at least 8000 years to the Sumerian coppersmiths as discussed by the authors, and physical understanding of the mechanisms involved, on the other hand, began little more than 50 years ago; modem knowledge suggests that even now this understanding is far from complete.
Abstract: The art of forming materials into technologically useful artifacts by manipulation of the dislocation substructure dates back at least 8000 years to the Sumerian coppersmiths.1 Physical understanding of the mechanisms involved, on the other hand, began little more than 50 years ago; modem knowledge suggests that even now this understanding is far from complete.
138 citations
TL;DR: In this article, the authors present an overview of recent work on quantum-based atomistic simulation of materials properties in transition metals performed in the Metals and Alloys Group at Lawrence Livermore National Laboratory.
Abstract: We present an overview of recent work on quantum-based atomistic simulation of materials properties in transition metals performed in the Metals and Alloys Group at Lawrence Livermore National Laboratory. Central to much of this effort has been the development, from fundamental quantum mechanics, of robust many-body interatomic potentials for bcc transition metals via model generalized pseudopotential theory (MGPT), providing close linkage between ab?initio electronic-structure calculations and large-scale static and dynamic atomistic simulations. In the case of tantalum (Ta), accurate MGPT potentials have been so obtained that are applicable to structural, thermodynamic, defect, and mechanical properties over wide ranges of pressure and temperature. Successful application areas discussed include structural phase stability, equation of state, melting, rapid resolidification, high-pressure elastic moduli, ideal shear strength, vacancy and self-interstitial formation and migration, grain-boundary atomic structure, and dislocation core structure and mobility. A number of the simulated properties allow detailed validation of the Ta potentials through comparisons with experiment and/or parallel electronic-structure calculations. Elastic and dislocation properties provide direct input into higher-length-scale multiscale simulations of plasticity and strength. Corresponding effort has also been initiated on the multiscale materials modelling of fracture and failure. Here large-scale atomistic simulations and novel real-time characterization techniques are being used to study void nucleation, growth, interaction, and coalescence in series-end fcc transition metals. We have so investigated the microscopic mechanisms of void nucleation in polycrystalline copper (Cu), and void growth in single-crystal and polycrystalline Cu, undergoing triaxial expansion at a large, constant strain rate - a process central to the initial phase of dynamic fracture. The influence of pre-existing microstructure on the void growth has been characterized both for nucleation and for growth, and these processes are found to be in agreement with the general features of void distributions observed in experiment. We have also examined some of the microscopic mechanisms of plasticity associated with void growth.
137 citations
References
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Book•
01 Jan 1968
TL;DR: Dislocations in Isotropic Continua: Effects of Crystal Structure on Dislocations and Dislocation-Point-Defect Interactions at Finite temperatures.
Abstract: Dislocations in Isotropic Continua. Effects of Crystal Structure on Dislocations. Dislocation-Point-Defect Interactions at Finite Temperatures. Groups of Dislocations. Appendixes. Author and Subject Indexes.
10,220 citations
01 Jan 1972
TL;DR: In this article, a model of a planar square lattice is used to simulate the effect of point defects on the Lattice Green Function. But the model is not suitable for the simulation of complex lattice models.
Abstract: One Introductory Lectures.- 1. Computer Experiments With Lattice Models.- Discussion.- 2. Potential Functions and the Simulation of Defects in Lattice Dynamical Defect Problems.- Discussion.- 3. The Theory of Interatomic Potentials in Solids...- Discussion.- 4. Ion-Ion Interactions in Metals: Their Nature and Physical Manifestations.- Discussion.- 5. Kanzaki Forces and Electron Theory of Displaced Charges in Relaxed Defect Lattices.- Discussion.- Two Interatomic Potentials.- 1. Screening Functions in Simple Metals.- Discussion.- 2. The Direct Construction of the Lattice Green Function.- Discussion.- 3. Computer Simulation of Quantum Phenomena.- Discussion.- 4. On the Validity of Two-Body Potentials in Metals.- Discussion.- 5. Experimental Techniques Used to Obtain Potentials.- Discussion.- 6. Molecular Dynamics Studies of Liquids.- Discussion.- 7. Interatomic Potentials Aspects Which are Visible in Experimental Radial Pair Distributions.- 8. Derivation of Long-Range Interaction Energies from Diffuse Scattering in Diffraction Patterns.- Discussion.- 9. The Study of Interatomic Potentials by Planar Channeling Experiments.- Discussion.- Three Point Defects.- 1. Defect Calculations for FCC and BCC Metals.- Discussion.- 2. Pseudopotential Calculation of Point Defect Properties in Simple Metals.- Discussion.- 3. Impurity Atom Effects in Metallic Crystals.- Discussion.- 4. Rare Gases in Metals.- Discussion.- 5. On Pseudopotential Calculation of Point Defects in Metals.- Discussion.- 6. Computer Simulation of the Short-Term Annealing of Displacement Cascades.- Discussion.- 7. Computer Simulation of Atomic Displacement Cascades in Solids.- Discussion.- 8. Temperature Dependence of the Vacancy Formation Energy in Krypton by Molecular Dynamics.- Discussion.- Agenda Discussion: Point Defects.- Four Dislocations and Stacking Faults.- 1. Influence of Dislocations on Electron Microscope Crystal Lattice Images.- Discussion.- 2. On the Motion of the a/2 Screw Dislocation in Models of ?-Iron.- Discussion.- 3. On the Factors Controlling the Structure of the Dislocation Cores in BCC Crystals.- Discussion.- 4. Extended Defects in Copper and Their Interactions with Point Defects.- Discussion.- 5. Partial Dislocation Interactions in a Face-Centered Cubic Sodium Lattice.- Discussion.- 6. The Motion of Screw Dislocations in a Model B.C.C. Sodium Lattice.- Discussion.- 7. Atomistic Calculations of Peierls-Nabarro Stress in a Planar Square Lattice.- Agenda Discussion: Dislocations and Stacking Faults.- Five Surfaces and Interfaces.- 1. Experimental Studies of Atomic Behavior at Crystal Surfaces.- Discussion.- 2. Simulating Surfaces by the Summation of Pairwise Interatomic Potentials.- Discussion.- 3. Interaction Energy and Configuration of Ledges on (001) Copper Surfaces.- Discussion.- 4. Computer Calculations of Dynamical Surface Properties of Crystals.- Discussion.- 5. A Computer Simulation Study of Grain Boundaries in FCC Gamma-Iron and Their Interactions With Point Defects.- Discussion.- 6. Computer Simulation of the Structure of High Angle Grain Boundaries.- Discussion.- 7. A Study of Crack Propagation in Alpha-Iron.- Discussion.- Agenda Discussion: Surfaces and Interfaces.- Six Computer Techniques.- Agenda Discussion: Computer Techniques.- Seven Critical Issues.- Concluding Agenda Discussion: Critical Issues.
512 citations
TL;DR: A relaxation-type calculation of the structure of the dislocation core has been made for the ½ 〈111〉 screw dislocation in b.c. crystals, using a variety of central-force potentials as discussed by the authors.
Abstract: A relaxation-type calculation of the structure of the dislocation core has been made for the ½ 〈111〉 screw dislocation in b.c.c. crystals, using a variety of central-force potentials. Two stable configurations were found, corresponding to the centre of the dislocation being along either the left-hand or the right-hand type of three-fold screw axis in the crystal. These two configurations differed only in the very centre. For both configurations and for all potentials, the core structure possessed three-fold symmetry, the largest displacements being in the directions in which displacements on (211) type planes were in the twinning sense. The structure can be described by a combination of large displacements on {110} type planes, plus ‘stacking faults’, 1–2b wide on {211} type planes in the twinning sense only. An investigation of the effect of boundary conditions showed that any errors caused by incomplete relaxation were negligible, and that changing the initial dislocation position or the positi...
414 citations
TL;DR: In this paper, the authors present nonlinear self-consistent calculations of the charge density induced by isolated ions when placed in an electron gas of the appropriate metallic density and show that in the first four metals nonlinear effects in the response of the conduction electrons to the ionic perturbations play an important role in determining charge density and the interionic potential.
Abstract: We present nonlinear self-consistent calculations of the charge density induced by isolated ${\mathrm{Li}}^{+}$, ${\mathrm{K}}^{+}$, ${\mathrm{Mg}}^{++}$, ${\mathrm{Al}}^{+++}$, and ${\mathrm{Ca}}^{++}$ ions when placed in an electron gas of the appropriate metallic density. By comparison with linear-response theory we show that in the first four metals nonlinear effects in the response of the conduction electrons to the ionic perturbations play an important role in determining the charge density and the interionic potential. However as in the case of Na studied in the previous paper these nonlinear effects can be simulated by using a suitably adjusted model potential. The calculated phonon dispersion curves for Li, K, and Al agree very well with experiment. Nonlinear effects are also very likely to be important in Ca but further work is necessary before conclusions can be drawn.
291 citations
TL;DR: In this paper, the behavior of the screw dislocation core in the presence of an external shear stress was examined for the body-centered cubic and hexagonal close-packed phases of a model sodium lattice.
Abstract: The behavior of the screw dislocation core in the presence of an external shear stress has been examined for the body-centered cubic and hexagonal close-packed phases of a model sodium lattice, usi...
227 citations