Lattice Monte Carlo analysis of vacancy diffusion

The lattice Monte Carlo method is a well-established technique for the simulation of solid-state transformation and diffusion processes. In this work, the impact of vacancy-solute binding on diffusion in binary alloys is investigated. The solute atom diffusivity increases monotonically with the vacancy preference toward the solute atom. The vacancy diffusivity is the fastest for the ideal solution case and decreases with the vacancy preference toward any of the alloy component. If the vacancy/trap binding energy is attractive, the impact of trapping on the mobility of vacancies is found to be significant. These observations are taken as a basis for the discussion of the diffusion of atoms and vacancies in binary aluminium systems

Monte-Carlo study of coherent bcc-Cu precipitation in alpha-iron

Coherent copper precipitation in supersaturated α-iron is simulated using the Monte Carlo method with the vacancy exchange mechanism. The influence of the various simulation parameters (temperature, copper content, nucleus size, bond energies) on the precipitate is investigated and compared with the continuum models. The copper solubility is reproduced with the bond energy values close to the parameters found in CALPHAD models. It is shown that an additional interfacial energy appears in the simulation depending on the radius size of the precipitate and attributable to the Gibbs-Thomson effect. Attention is also paid to the chemical composition and the thickness of the α-iron/bcc-Cu diffuse interface. A qualitative agreement with the predictions of the macroscopic description is found

Analysis of the influence of vacancy-solute interaction on diffusion of atomic monomers and clusters

Abstract version 2 for TMS 2011 San Diego John Agren Symposium Analysis of the influence of vacancy-solute interaction on diffusion of atomic monomers and clusters P. Warczok, J. Zenisek and E. Kozeschnik In the present paper, we investigate the dependence of the diffusional mobility of single solute atoms as well as clusters of atoms on the vacancy-solute binding characteristics with the Monte Carlo (MC) method. Existing work, mainly based on first-principles calculations and atomistic simulations, is reviewed first. Then, we compare these results to our simulations performed with MC and explore these effects in the light of macroscopic diffusive fluxes and atomic clusters movement in the sense of Brownian motion. Finally, we propose a numerical method for incorporation of the movement and potential collisions of clusters in a precipitation kinetics framework

Atomistic and continuums modeling of cluster migration and coagulation in precipitation reactions

AbstractThe influence of vacancy preference towards one of the constituents in a binary system on the formation of precipitates was investigated by atomistic and continuums modeling techniques. In case of vacancy preference towards the solute atoms, we find that the mobility of individual clusters as well as entire atom clusters is significantly altered compared to the case of vacancy preference towards the solvent atoms. The increased cluster mobility leads to pronounced cluster collisions, providing a precipitate growth and coarsening mechanism competitive to that of pure solute evaporation and adsorption considered in conventional diffusional growth and Ostwald ripening. A modification of a numerical Kampmann–Wagner type continuum model for precipitate growth is proposed, which incorporates the influence of both mechanisms. The prognoses of the modified model are validated against the growth laws obtained with lattice Monte Carlo simulations and a growth simulation considering solely the coalescence mechanism

Diffusion und Koagulation von Ausscheidungs-Clustern - Simulation auf atomistischer und Kontinuums-Skala

Diffusion und Koagulation von Ausscheidungs-Clustern - Simulation auf atomistischer und Kontinuums-Skala E Kozeschnik1,2, P. Warczok2, J. Zenisek2 1Christian Doppler Laboratory 'Early Stages of Precipitation', Institute of Materials Science and Technology, Vienna University of Technology, Favoritenstraße 9-11, 1040 Vienna. 2 Institute of Materials Science and Technology, Vienna University of Technology, Favoritenstraße 9-11, 1040 Vienna, Austria In kristallinen Werkstoffen können sich gelöste Atome mit Hilfe von Austauschprozessen zwischen Gitteratomen und Gitterleerstellen durch den Werkstoff bewegen. Im Falle abstoßender Wechselwirkung zwischen Matrix- und Fremdatom bilden sich unter geeigneten Voraussetzungen (Übersättigung) Ausscheidungen einer neuen Phase, die reicher an Fremdatomen ist als die Matrix. In klassischen Betrachtungen der Ausscheidungsbildung werden diese Partikel in der Regel als starre und unbewegliche Objekte angesehen, was für verdünnte Lösungen und geringe Ausscheidungsdichten auch eine sinnvolle Näherung darstellt. Bei konzentrierten Lösungen und hohen Ausscheidungsdichten darf die Bewegung der Ausscheidungen selbst, sei es durch die statistischen Absorptions- und Desorptionsprozesse oder durch die bevorzugte Einlagerung der Leerstellen in und um die Ausscheidungen, nicht mehr vernachlässigt werden. Die Entwicklung der Ausscheidungen in den frühen Stadien ist in diesem Fall maßgeblich von Kollisionsprozessen unter den Teilchen geprägt. In diesem Vortrag wird das Phänomen der Bewegung von Ausscheidungen am Beispiel des Fe-Cu Systems mit Hilfe der Monte Carlo Methode studiert und mit einem kontinuums-theoretischen Ansatz verglichen. Die Bewegung und Kollision von Ausscheidungen wird anhand anschaulicher Simulationsergebnisse demonstriert

Lattice Monte Carlo analysis of vacancy diffusion in the presence of discrete trapping

The lattice Monte Carlo method is a well-established technique for the simulation of solid-state transformation and diffusion processes. In this work, the impact of vacancy-solute binding on substitutional diffusion in binary alloys is investigated. Classic Metropolis algorithm is applied in the face centered cubic system with a single vacancy present and the interaction between the alloy components is set to zero (a random alloy). Number of jump attempts is interpreted in term of time variable and the vacancy migration is measured. The vacancy diffusivity is the fastest for the ideal solution case and decreases with the vacancy preference toward any of the alloy components. If the vacancy/solute binding energy is attractive, the impact of trapping on the mobility of vacancies is significant. The diffusion of the vacancy/solute complex can be hardly observed. The relation between the correlation factor of the vacancy movement and the vacancy jumps vacancies is analyzed. These observations are taken as a basis for a discussion of experimental diffusion coefficients of vacancies in binary Al alloys

Agile Multiscale Modelling of the Thermo-Mechanical Processing of an Aluminium Alloy

The multiscale modelling of the behaviour of metal alloys during processing is often limited by the computing power required to run them. The Agile Multiscale Methodology was conceived to enhance the designing and controlling of complex multiscale models through an automatic run-time adaptation of its constitutive sub-models. This methodology is used to simulate the behaviour of an 6082 aluminium alloy during its thermomechanical treatment. The macroscopic deformation, the work-hardening and the state of precipitation are computed in different modules, allowing the coupling of several software solutions (DEFORMTM2D and © MatCalc) through an external storage of the relevant data.</jats:p