D. Terentyev

Segregation of Cr at tilt grain boundaries in Fe-Cr alloys: A Metropolis Monte Carlo study

D. Terentyev, X. He, E. Zhurkin, A. Bakaev

Journal of Nuclear Materials

408, 161–170

2011

A1

Abstract

In this work, the Metropolis Monte Carlo (MMC) method employing the isothermal–isobaric statistical ensemble is applied to investigate segregation at grain boundaries in bcc Fe–Cr alloys with varying Cr content from 5 to 14 at.%. Several different 〈1 1 0〉 tilt grain boundaries, namely: Σ19{3 3 1}, Σ9{2 2 1}, Σ3{1 1 1}, Σ3{1 1 2}, Σ11{1 1 3}, Σ9{1 1 4} with misorientation angle varying in the range 26–141° were considered. Systematic MMC simulations were performed employing a two band empirical many-body potential in the temperature range 300–900 K. It was found that the binding energy of substitutional Cr to the GB core is essentially determined by the structure of the GB interface and varies in the range 0.05–0.35 eV. At this, the binding energy increases with the GB excess volume. MMC simulations revealed that either a local atomic rearrangement or segregation of Cr at the considered GBs occurs depending on the combination of temperature, alloy composition and GB structure. Influence of temperature and GB structure on the local atomic rearrangement and precipitation of α′ particles is demonstrated.

DOI

http://dx.doi.org/10.1016/j.jnucmat.2010.11.024

Interatomic potential to study plasticity in stainless steels: the FeNiCr model alloy

G. Bonny, D. Terentyev, R. C. Pasianot, S. Poncé, A. Bakaev

Modelling and Simulation in Materials Science and Engineering

19 (8), 085008

2011

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Abstract

Austenitic stainless steels are commonly used materials for in-core components of nuclear light water reactors. In service, such components are exposed to harsh conditions: intense neutron irradiation, mechanical and thermal stresses, and aggressive corrosion environment which all contribute to the components' degradation. For a better understanding of the prevailing mechanisms responsible for the materials degradation, large-scale atomistic simulations are desirable. In this framework we developed an embedded atom method type interatomic potential for the ternary FeNiCr system to model movement of dislocations and their interaction with radiation defects. Special attention has been drawn to the Fe–10Ni–20Cr alloy, whose properties were ensured to be close to those of 316L austenitic stainless steel. In particular, the stacking fault energy and elastic constants are well reproduced. The fcc phase for the Fe–10Ni–20Cr random alloy was proven to be stable in the temperature range 0–900 K and under shear strain up to 5%. For the same alloy the stable glide of screw dislocations and stability of Frank loops was confirmed.

DOI

http://dx.doi.org/10.1088/0965-0393/19/8/085008

On the thermal stability of vacancy–carbon complexes in alpha iron

D. Terentyev, G. Bonny, A. Bakaev, D. Van Neck

Journal of Physics: Condensed Matter

24, 385401

2012

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Abstract

In this work we have summarized the available ab initio data addressing the interaction of carbon with vacancy defects in bcc Fe and performed additional calculations to extend the available dataset. Using an ab initio based parameterization, we apply object kinetic
Monte Carlo (OKMC) simulations to model the process of isochronal annealing in bcc Fe doped with carbon to compare with experimental data. As a result of this work, we clarify that a binding energy of ~0.65 eV for a vacancy–carbon (V–C) pair fits the available experimental
data best. It is found that the V2–C complex is less stable than the V–C pair and its dissociation with activation energy of 0.55 + 0.49 eV also rationalizes a number of experimental data where the breakup of V–C complexes was assumed instead. From the summarized ab initio data, the subsequently obtained OKMC results and critical discussion, provided here, we suggest that the twofold interpretation of the V–C binding energy, which is believed to vary between 0.47 and 0.65 eV, depending on the ab initio approximation, should be removed. The stability and mobility of small and presumably immobile SIA clusters formed at stage II is also discussed in the view of experimental data.

DOI

http://dx.doi.org/10.1088/0953-8984/24/38/385401

Early stages of α-α′ phase separation in Fe-Cr alloys: An atomistic study

G. Bonny, D. Terentyev, L. Malerba, D. Van Neck

Physical Review B

79 (10), 104207

2009

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Abstract

The thermal aging of Fe-Cr alloys was simulated using atomistic kinetic Monte Carlo techniques. The study was performed varying the Cr content in the range of 12–18 at. % Cr and at temperatures within the miscibility gap, where α-α′ phase separation occurs. The evolution of the phase-separation process was characterized in terms of precipitate shape, composition, density, and mean size. The results offer a description of α-α′ phase separation in its early stage, which is hardly accessible to experiments and of key importance in understanding the change in mechanical properties of Fe-Cr alloys under thermal aging. The critical size for a stable precipitate was estimated from the simulation data in the framework of Gibbs's homogeneous nucleation theory. The obtained results are compared, whenever possible, with available experimental data and the reliability, as well as the shortcomings, of the applied method is discussed accordingly. Despite strong oversimplifications, the used model shows good agreement with experimental data.