Metropolis Monte Carlo simulations of ordering and clustering in FeCr alloys
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1125-R07-37
Metropolis Monte Carlo simulations of ordering and clustering in FeCr alloys Evgeny E. Zhurkin1, 2, Romain Pereira3, Nicolas Castin4, Lorenzo Malerba4, Marc Hou2 Experimental Nuclear Physics Department K-89, Faculty of Physics and Mechanics, SaintPetersburg State Polytechnical University, 29 Polytekhnicheskaya str., 195251 St.Petersurg, Russian Federation 2 Physique des Solides Irradiés et des Nanostrucutres CP234, Faculté des Sciences, Université Libre de Bruxelles, Bd du Triomphe, B-1050 Bruxelles, Belgium. 3 INSTN, CEA Saclay, Gif sur Yvette, France 4 Structural Material Group, Institute of Nuclear Materials Science, SCK•CEN, Mol, Belgium 1
ABSTRACT The Metropolis Monte Carlo (MMC) algorithm is a computational method to study equilibrium thermodynamic properties of a system at the atomic level. The algorithm accounts for all terms that contribute to defining the free energy difference between states: not only chemical, configurational and interfacial, but also due to strain fields and thermal vibrations. In this work, the MMC method with a two bands empirical many-body potential is used to predict the ordering properties of Fe1-xCrx alloys at various compositions and temperatures in the absence of defects. The particular goal of the work was to reveal the effect of atomic relaxations and vibrations on the phase diagram. It is found that vibrations and local relaxation effects contribute to lowering the order-disorder transition temperature by about 25 percent as compared to MMC predictions with a rigid lattice. INTRODUCTION The binary Fe-Cr system has been extensively investigated over the last few decades, for its great interest in industrial, especially nuclear, applications. The conventionally accepted phase diagram that can be found in handbooks [1] essentially coincides with the CALPHAD formulation proposed in 1987 [2], based on high-temperature ageing data. However, it has been recently shown that the low temperature part of the diagram representing α-α' boundary (in alloys containing less that 15% of Cr) exhibits much larger Cr solubility than expected from the hightemperature extrapolation [3,4]. Preliminary sets of calculations employing many-body empirical potentials have shown a surprisingly good agreement with many experimental data that were recently compiled in [3]. In this work, we continue to study phase separation in the Fe-Cr alloys and cover a wide range of Cr content using one of the same cohesive models used in [3]. To do so we apply Metropolis Monte Carlo (MMC) simulations sampling [5] within the isothermal-isobaric statistical ensemble, which allows equilibrium thermodynamic properties of a system at the atomic level to be assessed. Such an algorithm accounts for the several terms determining the free energy, i.e. compositional, configurational, interfacial and also vibrational (originating from the lattice temperature effects), as well as due to strain fields. While the sequence of configurations visited using MMC does not represent a physical trajectory, this method does not
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