Atomistic simulation of He bubble in Fe as obstacle to dislocation (original) (raw)
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Atomistic simulations of dislocations and defects
Journal of computer-aided …, 2002
This paper reviews selected recent research on the atomistic simulation of dislocation and defect properties of materials relevant to the multiscale modeling of plasticity and strength, with special emphasis on bcc metals and including work at extreme conditions. Current topics discussed include elasticity and ideal strength, dislocation structure and mobility, grain boundaries, point defects, and rapid resolidification, as well as noteworthy examples of research that directly impacts the issue of linking of length and/or time scales, as required in multiscale materials modeling. The work reviewed has been inspired by the recent international Workshop on Multiscale Modeling of Materials Strength and Failure held in October 2001 at Bodega Bay, California.
Atomistic simulation of dislocation nucleation and motion from a crack tip
Acta Materialia, 1997
A recently developed fully atomistic technique for fracture simulations is applied to the study of dislocation emission from a crack tip in an elastically anisotropic f.c.c. crystal. The detailed atomicscale mechanisms of dislocation nucleation and motion are investigated as a function of the external load. Analysis of the atomic configurations around the crack tip demonstrates an intimate coupling of the nucleating dislocation with a step formed at the crack surface. Displacement and stress fields around both nucleating and moving dislocations are compared to the predictions of the Peierls-Nabarro continuum-elastic model by Rice. The size of a nucleating ("incipient") dislocation is found to be larger than that of a fully-formed dislocation. Also, we elucidate the reasons why the value of the unstable-stacking energy estimated by means of the rigid-block sliding concept, a feature common to several continuum-elastic models, overestimates the activation energy for dislocation nucleation. We conclude that the concept of unstable-stacking energy should be replaced by the true energy barrier for dislocation nucleation, incorporating the full inhomogeneity of the displacement field.
International Journal of Plasticity, 2019
Multiscale discrete dislocation plasticity (MDDP) simulations are carried out to investigate the mechanical response and microstructure evolution of single crystal BCC iron subjected to high strain rate compression over a wide range of temperature. The simulations are conducted at temperatures ranging between 300K to 900K and strain rate ranging between10 2 to10 7 s-1. Atomistically informed generalized mobility law was incorporated in MDDP to account for the effects of temperature and strain rate on dislocation mobility, lattice friction and elastic constants. MDDP based constitutive equations interrelating temperature and strain rate with the flow stress at high strain rate shock-less and shock conditions are proposed. The simulation results of the temperature and strain rate dependent yield strength and Hugoniot elastic limit are in good agreement with reported experimental results. Detailed investigations of the dislocation microstructure evolution show the formation of extended screw dislocation lines at temperatures below 340 K due to the large value of the lattice friction of the pure screw segments. Moreover, small sessile loops of radius in the order of few nanometers are formed. The formation of these sessile loops is facilitated by the easiness of multiple cross slip on available slip planes.
Journal of Nuclear Materials, 2002
During irradiation, mobile defects, defect clusters and impurity atoms segregate on dislocations. When an external stress is applied, plastic flow is initiated when dislocations are unlocked from segregated defects. Sustained plasticity is achieved by continuation of dislocation motion, overcoming local forces due to dispersed defects and impurities. The phenomena of flow localization, post-yield hardening or softening and jerky flow are controlled by dislocation-defect interactions. We review here computational methods for investigations of the dynamics of dislocation-defect interactions. The influence of dislocations on the motion of glissile self-interstitial atoms (SIAs) and their clusters is explored by a combination of kinetic Monte Carlo and dislocation dynamics. We show that dislocation decoration by SIAs is a result of their 1-D motion and rotation as they approach dislocation cores. The interaction between dislocations and immobilized SIA clusters indicates that the unlocking mechanism is dictated by shape instabilities. Finally, computer simulations for the interaction between freed dislocations and stacking fault tetrahedra in irradiated Cu, and between dislocations and microvoids in irradiated iron are presented, and the results show good agreement with experimental observations.
Dislocation decoration and raft formation in irradiated materials
Philosophical Magazine, 2005
Experimental observations of dislocation decoration with self-interstitial atom (SIA) clusters and of SIA cluster rafts are analysed to establish the mechanisms controlling these phenomena in bcc metals. The elastic interaction between SIA clusters, and between clusters and dislocations is included in kinetic Monte Carlo (KMC) simulations of damage evolution in irradiated bcc metals. The results indicate that SIA clusters, which normally migrate by 1D glide, rotate due to their elastic interactions, and that this rotation is necessary to explain experimentally-observed dislocation decoration and raft formation in neutronirradiated pure iron. The critical dose for raft formation in iron is shown to depend on the intrinsic glide/rotation characteristics of SIA clusters. The model is compared with experimental observations for the evolution of defect cluster densities (sessile SIA clusters and nano-voids), dislocation decoration characteristics and the conditions for raft formation.
Atomistic simulations of dislocation formation at surface defects
Dislocation formation at surface defects concerns in general nanostructured materials subjected to large stresses. An important case is that of epitaxial structures, films or multilayers, where large stresses result from a crystal lattice mismatch; such structures are built up for example in microelectronic devices. Below ten nanometers, the domain size is too small to allow for dislocation multiplication. The observed dislocations must have formed at surfaces or interfaces and particularly at their defects. For example, in silicon, steps present at crack surfaces are observed to enhance the formation of dislocations .
Communications Materials
Dislocation loops are ubiquitous in irradiated materials, and dislocation loop bias plays a critical role in void swelling. However, due to complicated interactions between dislocation loops and point defects, it is challenging to evaluate the bias factors of dislocation loops. Here, we determine the bias of sessile < 100 > loops in α-iron using a recently developed atomistic approach based on the lifetime of point defects. We establish a mechanistic understanding of the loop interaction based on the diffusion tendency of point defects near the loop core region. Mobile self-interstitial atoms tend to be absorbed from the edge of the loop, and a trapping region perpendicular to the habit plane of the loop exists. The dislocation loop bias is found to be substantially lower than those of straight dislocations in α-iron and should be included in swelling rate estimates. With the obtained sink strength and bias values, agreement is achieved with experimental results for both absol...
Coarse-grained atomistic simulation of dislocations
Journal of the Mechanics and Physics of Solids, 2011
This paper presents a new methodology for coarse-grained atomistic simulation of dislocation dynamics. The methodology combines an atomistic formulation of balance equations and a modified finite element method employing rhombohedral-shaped 3D solid elements suitable for fcc crystals. With significantly less degrees of freedom than that of a fully atomistic model and without additional constitutive rules to govern dislocation activities, this new coarse-graining (CG) method is shown to be able to reproduce key phenomena of dislocation dynamics for fcc crystals, including dislocation nucleation and migration, formation of stacking faults and Lomer-Cottrell locks, and splitting of stacking faults, all comparable with fully resolved molecular dynamics simulations. Using a uniform coarse mesh, the CG method is then applied to simulate an initially dislocation-free submicron-sized thin Cu sheet. The results show that the CG simulation has captured the nucleation and migration of large number of dislocations, formation of multiple stacking fault ribbons, and the occurrence of complex dislocation phenomena such as dislocation annihilation, cutting, and passing through the stacking faults. The distinctions of this method from existing coarse-graining or multiscale methods and its potential applications and limitations are also discussed.
Molecular dynamics simulation of dislocation–void interactions in BCC Mo
Journal of Nuclear Materials, 2009
The molecular dynamics method is used to simulate dislocation intersection in aluminum containing 1.6 × 10 6 atoms using embedded atom method (EAM) potential. The results show that after intersection between two right-hand screw dislocations of opposite sign there are an extended jog corresponding to a row of 1/3 vacancies in the intersected dislocation, and a trail of vacancies behind the moving dislocation. After intersection between screw dislocations of same sign, there are an extended jog corresponding to a row of 1/3 interstitials in the intersected dislocation, and a trail of interstitials behind the moving dislocation. After intersection between screw and edge dislocations with different Burgers vector, there are a constriction corresponding to one 1/3 vacancy in the edge dislocation, and no point-defects behind the screw dislocation. When a moving screw dislocation intersects an edge dislocation with the same Burgers vector, the point of intersection will split into two constrictions corresponding to one 1/3 vacancy and 1/3 interstitial, respectively. The moving screw dislocation can pass the edge dislocation only after the two constrictions, which can move along the line of intersection of the two slip planes, meet and annihilate.