Normand Mousseau
Professeur de physique et directeur académique
de l'Institut de l'énergie Trottier

Oscar Restrepo

Chercheur post-doctoral

Projet de recherche

  • Caractérisation des mécanismes de diffusion et d’interaction du C dans le fer.

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Articles en collaboration

  • S. Mahmoud, M. Trochet, O. A. Restrepo, N. Mousseau, Study of point defects diffusion in nickel using kinetic activation-relaxation technique, Acta Materialia 144, 679-690 (2018).
    Résumé : Abstract Point defects play a central role in materials properties. Yet, details regarding their diffusion and aggregation are still largely lacking beyond the monomer and dimer. Using the kinetic Activation Relaxation Technique (k-ART), a recently proposed off-lattice kinetic Monte Carlo method, the energy landscape, kinetics and diffusion mechanisms of point defect in fcc nickel are characterized, providing an exhaustive picture of the motion of one to five vacancies and self-interstitials in this system. Starting with a comparison of the prediction of four empirical potentials — the embedded atom method (EAM), the original modified embedded atom method (MEAM1NN), the second nearest neighbor modified embedded atom method (MEAM2NN) and the Reactive Force Field (ReaxFF) —, it is shown that while both EAM and ReaxFF capture the right physics, EAM provides the overall best agreement with ab initio and molecular dynamics simulations and available experiments both for vacancies and interstitial defect energetics and kinetics. Extensive k-ART simulations using this potential provide complete details of the energy landscape associated with these defects, demonstrated a complex set of mechanisms available to both vacancies and self-interstitials even in a simple environment such as crystalline Ni. We find, in particular, that the diffusion barriers of both vacancies and interstitials do not change monotonically with the cluster size and that some clusters of vacancies diffuse more easily than single ones. As self-interstitial clusters grow, moreover, we show that the fast diffusion takes place from excited states but ground states can act as pinning centers, contrary to what could be expected.
    Mots-clés : Diffusion mechanisms, Energy landscape, Kinetic Activation Relaxation Technique, Nickel, Self-defect.

  • O. A. Restrepo, N. Mousseau, M. Trochet, F. El-Mellouhi, O. Bouhali, C. S. Becquart, Carbon diffusion paths and segregation at high-angle tilt grain boundaries in \ensuremath\alpha-Fe studied by using a kinetic activation-relation technique, Phys. Rev. B 97, 054309 (2018).

  • O. A. Restrepo, C. S. Becquart, F. El-Mellouhi, O. Bouhali, N. Mousseau, Diffusion mechanisms of C in 100, 110 and 111 Fe surfaces studied using kinetic activation-relaxation technique, Acta Materialia 136, 303 - 314 (2017).
    Résumé : The physics of Fe-C surface interactions is of fundamental importance to phenomena such as corrosion, catalysis, synthesis of graphene, new steels, etc. To better understand this question, we perform an extensive characterization of the energy landscape for carbon diffusion from bulk to surfaces for bcc iron at low C concentration. C diffusion mechanisms over the three main Fe-surfaces – (100), (110) and (111) – are studied computationally using the kinetic activation-relaxation technique (k-ART), an off-lattice kinetic Monte Carlo algorithm. Migration and adsorption energies on surfaces as well as absorption energies into the subsurfaces are predicted and then compared to density functional theory (DFT) and experiment. The energy landscape along C-diffusion pathways from bulk to surface is constructed allowing a more extensive characterization of the diffusion pathways between surface and subsurface. In particular, effective migration energies from (100), (110) and (111) surfaces, to the bulk octahedral site are found to be around ∼1.6 eV, ∼1.2 eV and ∼1.3 eV respectively suggesting that C insertion into the bulk cannot take place in pure crystalline Fe, irrespective of the exposed surface.
    Mots-clés : ARTc, Migration energy.

  • I. H. Sahputra, A. Chakrabarty, O. A. Restrepo, O. Bouhali, N. Mousseau, C. S. Becquart, et al., Carbon adsorption on and diffusion through the Fe(110) surface and in bulk: Developing a new strategy for the use of empirical potentials in complex material set-ups, physica status solidi (b) 254, 1600408–n/a (2017).
    Résumé : Oil and gas infrastructures are submitted to extreme conditions and off-shore rigs and petrochemical installations require expensive high-quality materials to limit damaging failures. Yet, due to a lack of microscopic understanding, most of these materials are developed and selected based on empirical evidence leading to over-qualified infrastructures. Computational efforts are necessary, therefore, to identify the link between atomistic and macroscopic scales and support the development of better targeted materials for this and other energy industry. As a first step towards understanding carburization and metal dusting, we assess the capabilities of an embedded atom method (EAM) empirical force field as well as those of a ReaxFF force field using two different parameter sets to describe carbon diffusion at the surface of Fe, comparing the adsorption and diffusion of carbon into the 110 surface and in bulk of α-iron with equivalent results produced by density functional theory (DFT). The EAM potential has been previously used successfully for bulk Fe–C systems. Our study indicates that preference for C adsorption site, the surface to subsurface diffusion of C atoms and their migration paths over the 110 surface are in good agreement with DFT. The ReaxFF potential is more suited for simulating the hydrocarbon reaction at the surface while the subsequent diffusion to subsurface and bulk is better captured with the EAM potential. This result opens the door to a new approach for using empirical potentials in the study of complex material set-ups.
    Mots-clés : adsorption, ARTc, carbon, density functional theory, diffusion, embedded atom method, empirical potential, iron, matériaux.

  • O. A. Restrepo, N. Mousseau, F. El-Mellouhi, O. Bouhali, M. Trochet, C. S. Becquart, Diffusion properties of Fe–C systems studied by using kinetic activation–relaxation technique, Computational Materials Science 112, Part A, 96-106 (2016).
    Résumé : Diffusion of carbon in iron is associated with processes such as carburization and the production of steels. In this work, the kinetic activation–relaxation technique (k-ART) – an off-lattice self-learning kinetic Monte Carlo (KMC) algorithm – is used to study this phenomenon over long time scales. Coupling the open-ended ART nouveau technique to generate on-the-fly activated events and NAUTY, a topological classification for cataloging, k-ART reaches timescales that range from microseconds to seconds while fully taking into account long-range elastic effects and complex events, characterizing in details the energy landscape in a way that cannot be done with standard molecular dynamics (MD) or KMC. The diffusion mechanisms and pathways for one to four carbon interstitials, and a single vacancy coupled with one to several carbons are studied. In bulk Fe, k-ART predicts correctly the 0.815 eV barrier for a single C-interstitial as well as the stressed induced energy-barrier distribution around this value for 2 and 4 C interstitials. For vacancy–carbon complex, simulations recover the DFT-predicted ground state. K-ART also identifies a trapping mechanism for the vacancy through the formation of a dynamical complex, involving C and neighboring Fe atoms, characterized by hops over barriers ranging from ∼0.41 to ∼0.72 eV that correspond, at room temperature, to trapping time of hours. At high temperatures, this complex can be broken by crossing a 1.5 eV barrier, leading to a state ∼0.8 eV higher than the ground state, allowing diffusion of the vacancy. A less stable complex is formed when a second C is added, characterized by a large number of bound excited states that occupy two cells. It can be broken into a V–C complex and a single free C through a 1.11 eV barrier.
    Mots-clés : ARTc.

  • N. Mousseau, P. Brommer, J. - F. Joly, L. K. Béland, F. El-Mellouhi, G. K. N'Tsouaglo, et al., Following atomistic kinetics on experimental timescales with the kinetic Activation-Relaxation Technique, Computational Materials Science 100, 111-123 (2015).
    Mots-clés : ARTc.
mardi 1er juillet 2014

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