Intermittent dislocation flow in viscoplastic deformation

The viscoplastic deformation (creep) of crystalline materials under constant stress involves the motion of a large number of interacting dislocations. Analytical methods and sophisticated `dislocation-dynamics' simulations have proved very effective in the study of dislocation patterning, and have led to macroscopic constitutive laws of plastic deformation. Yet, a statistical analysis of the dynamics of an assembly of interacting dislocations has not hitherto been performed. Here we report acoustic emission measurements on stressed ice single crystals, the results of which indicate that dislocations move in a scale-free intermittent fashion. This result is confirmed by numerical simulations of a model of interacting dislocations that successfully reproduces the main features of the experiment. We find that dislocations generate a slowly evolving configuration landscape which coexists with rapid collective rearrangements. These rearrangements involve a comparatively small fraction of the dislocations and lead to an intermittent behavior of the net plastic response. This basic dynamical picture appears to be a generic feature in the deformation of many other materials. Moreover, it should provide a framework for discussing fundamental aspects of plasticity, that goes beyond standard mean-field approaches that see plastic deformation as a smooth laminar flow

Modelling precipitation in binary alloys by cluster dynamics

ISI Document Delivery No.: 419VV Times Cited: 0 Cited Reference Count: 19 Lepinoux, J. Pergamon-elsevier science ltd OxfordCluster dynamics is an original way to bridge the gap between atomistic Simulations and macroscopic approaches of precipitation, but its application to alloys Of high Solubility limit and solute concentration raise a number of difficulties. The underlying thermodynamic model has been recently extended to treat this type of situation. New tools are presented to explore some of the consequences of this with kinetic Monte-Carlo simulations. extension. validated by comparing (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved

Contribution of matrix frustration to the free energy of cluster distributions in binary alloys

International audienceA generalized version of Frenkel's model of cluster gas is proposed to provide a rigorous description of the contribution of the configuration entropy to the total free energy of cluster distributions in binary alloy. It is shown that the predicted cluster distributions are in excellent agreement with those obtained in kinematical Monte Carlo simulations. The emission and absorption coefficients to be used in cluster dynamics are fully defined: they depend not only of the free energy of clusters but also of the whole cluster distribution. Alternatively, this model can provide accurate values of the nucleation driving force used in classical nucleation theory

Precipitate growth in concentrated binary alloys: a comparison between kinetic Monte Carlo simulations, cluster dynamics and the classical theory

International audienceThe numerical modelling of concentrated alloy precipitation kinetics remains a challenge at all scales. At the microscopic scale, kinetic Monte Carlo (KMC) simulations can cope with nucleation and early growth whatever the solute concentration may be; it cannot, however, address coarsening. At the mesoscopic scale, the advantage of cluster dynamics (CD) is its ability to describe the whole kinetics of precipitation but lacks of reliability for nucleation in concentrated alloys. Finally, analytical models are preferred at the macroscopic scale for their simplicity, their flexibility and their ability to be incorporated within more general approaches, to predict mechanical properties, for instance. The present work aims at examining the ability of CD and classical analytical models to describe the growth of an isolated precipitate in a concentrated binary alloy, by comparison with KMC simulations taken as the reference

On the effect of concentrated solid solutions on properties of clusters in a model binary alloy

International audienceIn a series of papers aimed at better understanding precipitation in binary alloys, it was shown that Cluster Dynamics (CD) is a valuable tool to bridge the gap between microscopic and macroscopic scales, provided that cluster-free energies are carefully derived from Monte Carlo calculations. Indeed, in such conditions, CD predictions compare well with Atomistic Kinetic MC simulations. Nevertheless, in a recent work, the authors pointed out some limitations of this approach at high solute concentration. The present work aims at revisiting the notion of cluster-free energy in the context of concentrated solid solutions at thermal equilibrium

Grain growth in Damascene interconnects

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Application of cluster dynamics modeling to the precipitation in aluminum alloys

International audienceThe cluster dynamics method is used to model at the atomic scale the kinetics of first order phase transformations. Clusters are embryos of the growing phase. Their formation kinetics from the solid solution are obtained by solving a set of master differential equations. This set is the continuity equation of the cluster size distribution function and is based on inter-cluster solute exchanges. These exchanges, absorption and emission of solute atoms, are controlled by the solute diffusivities and the cluster free energies. The model is applied here to the precipitation of Al-3(Zr, Sc) dispersoids with the Ll(2) structure in Al-rich Zr-Sc solid solutions. Several characteristic features are obtained and discussed: 1) In the ternary alloy, the fast (Sc) diffusing species always controls the nucleation, in contrast to classical thermodynamical descriptions. 2) A Zr-Sc thermodynamic coupling induces heterogeneous nucleation on Zr atoms. 3) A segregation on the dispersoids outer shell of the slow diffusing solute (Zr) occurs during the coarsening stage, slowing down their coarsening rate. Finally, some extensions and prospects of the method are considered

Mechanisms and kinetics of recrystallisation:A two dimensional vertex dynamics simulation

The recrystallisation process in single phase materials is investigated using a vertex dynamics simulation. The situation is idealised (two dimensional and isotropic) to better understand the role of physical parameters (energy and mobility of subgrain and grain boundaries, shape and relative size of grains) on the competition between recrystallisation and recovery. Simulations show that subgrain growth can be very heterogeneous in the vicinity of grain boundaries, i.e. that recrystallisation develops following the bulging mechanism. Bulging is enhanced for low mobilities of subgrain boundaries, high relative desorientation and small relative sizes. The recrystallisation kinetics is well described by an Avrami law of low exponent

Modeling grain growth and related phenomena with vertex dynamics

International audienceGrain growth is the simplest phenomena related to the evolution of a population of grains in crystalline materials. Some typical results obtained with vertex dynamics, a deterministic technique applied to the simulation of grain growth in polycrystalline materials, mostly in two dimensions (2D), are presented: (i) the dynamics of a population of grains interacting with various distributions of pinning obstacles; (ii) bulging as a possible recrystallization mechanism; and (iii) the influence of a confined geometry on grain growth as those found in electronic devices. Finally recent developments in 3D are presented