Modeling of grain boundary dynamics using amplitude equations

We discuss the modelling of grain boundary dynamics within an amplitude equations description, which is derived from classical density functional theory or the phase field crystal model. The relation between the conditions for periodicity of the system and coincidence site lattices at grain boundaries is investigated. Within the amplitude equations framework we recover predictions of the geometrical model by Cahn and Taylor for coupled grain boundary motion, and find both $\langle100\rangle$ and $\langle110\rangle$ coupling. No spontaneous transition between these modes occurs due to restrictions related to the rotational invariance of the amplitude equations. Grain rotation due to coupled motion is also in agreement with theoretical predictions. Whereas linear elasticity is correctly captured by the amplitude equations model, open questions remain for the case of nonlinear deformations.Comment: 21 pages. We extended the discussion on the geometrical nonlinearities in Section

Reactive Objects

In the reactive approach, system components are not supposed to execute at their own rate, but are instead driven by a logical common clock, defining global instants. The Reactive Object Model introduced in this paper, is an object based formalism matching the reactive paradigm. In this model, methods can be invoked using instantaneous non-blocking send orders, which are immediately processed (that is, processed during the current instant); moreover, a method cannot execute more than once at each instant. The Reactive Object Model is described and compared to the Actor Model; then a prototype language based on this model is introduced; finally its expressive power is shown on the example of a broadcast communication mechanism

Maximum aspect ratio of a coherent nanowire at equilibrium

Nanostructures elongated perpendicular to their supporting substrate have attracted attention owing to their ability to sustain the coherency at the interface with the misfitting substrate. Here simple qualitative scaling arguments are used to derive the equilibrium aspect ratio of an elongated coherent cylindrical nanowire depending on its volume V. It is found to increase as V1/4. Using the usual law for the critical radius of nanowires, the maximum aspect ratio of a coherent nanowire is found to increase linearly with the lattice misfit, demonstrating that coherent nanowires with large aspect ratios exist at equilibrium for large misfits. In addition, it is shown that when the height of the coherent crystal is limited, a possible equilibrium state consists of an assembly of non-interacting nanowires

Etude du vieillissement des superalliages à base nickel par la méthode de champs de phase

PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Phase-field simulations with inhomogeneous elasticity: Comparison with an atomic-scale method and application to superalloys

We present a 2D and 3D phase-field analysis of microstructure evolution in the presence of a lattice misfit and with inhomogeneous elastic constants. The method is first critically compared with a Monte Carlo modeling at the atomic scale. We then apply the phase-field model to the Ni–Al system under external load along a cubic axis. We find that the microstructure becomes anisotropic and that the situation qualitatively differs depending on the sign of the applied stress. The microstructure evolution operates mainly by shape changes and alignments of precipitates, but also by splitting of precipitates initially elongated along directions perpendicular to the stress-induced, elastically favorable directions. The final microstructure is finally qualitatively analyzed in terms of a mean field theory in which the elastic inhomogeneity is embedded into an effective eigenstrain. This analysis leads to a simple formulation which can be used to easily predict the coherent microstructural anisotropy induced by any external loading condition

Elimination of surface diffusion in the non-diagonal phase field model

We present a non-diagonal phase field model for phase transformations with unequal but finite diffusivities in the two phases. This model allows to recover the desired boundary conditions at the diffuse interface, and especially the elimination of the artificially enhanced surface diffusion effect. The model is non-diagonal since it incorporates the kinetic cross-coupling between the non-conserved and the conserved fields that was recently introduced (Brener and Boussinot in Phys Rev E 86:060601, 2012). We test numerically this model for the two-dimensional relaxation of a weakly perturbed interface towards its flat equilibrium

La Programmation par Objets Réactifs (POR)

. We introduce a new programming model based on the object oriented approach, the reactive approach and the broadcast communication. In this model, interactions between objects are described in a natural way. At last, we present an implementation realized with the C++ and RC languages. Key Words. Concurrent object-oriented programming. Reactive programming. Events and broadcast communication. Introduction La programmation orient'ee objet, dont les concepts sont apparus avec le langage SIMULA [DMN68], connait `a l'heure actuelle un essor consid'erable et trouve des applications dans de nombreux domaines. Elle se caract'erise par une programmation qui regroupe (encapsule) les donn'ees et les op'erations sur celles-ci en une seule entit'e appel'ee objet. Cette vision localis'ee des informations et l'ind'ependance entre les objets engendrent un besoin naturel de distribution et de parall'elisme. La plupart des langages orient'es objets actuels soit sont s'equentiels (C++ [Stou86], CLOS [..

Quantitative nondiagonal phase field modeling of eutectic and eutectoid transformations

We develop a three-phase field model for the simulation of eutectic and eutectoid transformations on the basis of a nondiagonal model obeying Onsager relations for a kinetic cross coupling between diffusion and the phase fields. This model overcomes the limitations of existing phase field models concerning the fulfillment of local equilibrium boundary conditions at the transformation fronts in the case of a finite diffusional contrast between the phases. We benchmark our model in the well understood one-sided case with diffusion only in the parent phase against results from the literature. In addition to this solidification scenario, the case of solid-state transformations with diffusion in the growing phases is investigated. Our simulations validate the relevance of the theory developed by Ankit et al. [Acta Mater. 61, 4245 (2013)], that describes in a single frame the two limiting regimes where diffusion mainly takes place whether in the mother phase or in the growing phases. In both the one-sided and two-sided cases, we verify the necessity of the kinetic cross coupling for quantitative phase field simulations