6 research outputs found

    A tight-binding potential for atomistic simulations of carbon interacting with transition metals: Application to the Ni-C system

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    We present a tight-binding potential for transition metals, carbon, and transition metal carbides, which has been optimized through a systematic fitting procedure. A minimal basis, including the s, p electrons of carbon and the d electrons of the transition metal, is used to obtain a transferable tight-binding model of the carbon-carbon, metal-metal and metal-carbon interactions applicable to binary systems. The Ni-C system is more specifically discussed. The successful validation of the potential for different atomic configurations indicates a good transferability of the model and makes it a good choice for atomistic simulations sampling a large configuration space. This approach appears to be very efficient to describe interactions in systems containing carbon and transition metal elements

    III. – INTERSTITIAL COMPOUNDS.ORDER AND DISORDER IN CARBIDES AND NITRIDES

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    Nous présentons une revue expérimentale des propriétés de mise en ordre à courte et longue distance des défauts ponctuels dans les carbures et nitrures métalliques de métaux de transition, de terres rares et d'actinides. Nous insisterons sur le cas des lacunes de carbone dans les monocarbures de structure NaCl, où l'ordre semble pouvoir être décrit par des modèles géométriques très simples, en termes de couches de coordinence pour les atomes de métal, et être dû à des effets chimiques à courte distance plutôt qu'à des interactions élastiques à longue distance. Nous considérerons plus brièvement les mononitrures MNx de structure NaCl, les hémicarbures hexagonaux M2C, les phases dzéta M4C3-x, les solutions solides de haute température MC-MC2 et l'orientation ordonnée de paires de carbones dans les dicarbures MC2.We present a review of the general experimental evidence for short and long-range ordering of point defects in metallic transition metal, rare earth and actinide carbides and nitrides. Emphasis will be put on the case of carbon vacancies in the rocksalt structure monocarbides, where the ordering seems to be describable in very simple geometrical terms, with preferred coordination shells for the metal atoms, and due to short-range chemical effects rather than to long-range elastic interactions. We shall consider more briefly the rocksalt mononitrides MNx, the hexagonal hemicarbides M2C, the dzeta phases M4C3-x, the MC-MC2 high temperature solid solutions and the orientational ordering of carbon pairs in the MC2 dicarbides

    Equilibrium Phase Diagrams

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