A. Bakaev

Glide of dislocations in < 1 1 1 >{321} slip system: an atomistic study

D. Terentyev, A. Bakaev, D. Van Neck, E. Zhurkin
Philosophical Magazine
96 (1), 71-83
2016
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Abstract 

Atomistic calculations are performed to investigate plastic slip in the {321} system in body-centred cubic iron. Several modern interatomic potentials, developed over the last decade, are applied to compute the stacking fault -line energy in the {321} plane and the results are compared with the ab initio prediction. The applied potentials have shown strong deviations, but several potentials acquired good qualitative agreement with the ab initio data. Depending on the applied potential, the lowest value of the Peierls stress for the edge dislocation (ED) is 50MPa (Ackland and Bacon from 1997) and the highest is 550MPa (Dudarev and Derlet from 2005), while for the screw dislocation it is much higher, in the range 1-2GPa. At finite temperature, however, the flow stress of the ED is found to decrease exponentially reaching a negligible value at about 200K, irrespective of the applied potential. On the basis of the data obtained using Ackland-Mendelev potential from 2004, we conclude that the slip resistance of the {321} system is in between the resistance of the {110} and {112} slip systems.

Interaction of carbon-vacancy complex with minor alloying elements of ferritic steels

A. Bakaev, D. Terentyev, X. He, E. Zhurkin, D. Van Neck
Journal of Nuclear Materials
451 (1-3), 82-87
2014
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Abstract 

Interstitial carbon, dissolved in bcc matrix of ferritic steels, plays an important role in the evolution of radiation-induced microstructure since it exhibits strong interaction with vacancies. Frequent formation and break-up of carbon-vacancy pairs, occurring in the course of irradiation, affect both kinetics of the accumulation of point defect clusters and carbon spatial distribution. The interaction of typical alloying elements (Mn, Ni, Cu, Si, Cr and P) in ferritic steels used as structural materials in nuclear reactors with a carbon-vacancy complex is analyzed using ab initio techniques. It is found that all the considered solutes form stable triple clusters resulting in the increase of the total binding energy by 0.2-0.3 eV. As a result of the formation of energetically favourable solute-carbon-vacancy triplets, the dissociation energy for vacancy/carbon emission is also increased by similar to 0.2-0.3 eV, suggesting that the solutes enhance thermal stability of carbon-vacancy complex. Association of carbon-vacancy pairs with multiple solute clusters is found to be favorable for Ni, Cu and P. The energetic stability of solute(s)-carbon-vacancy complexes was rationalized on the basis of pairwise interaction data and by analyzing the variation of local magnetic moments on atoms constituting the clusters. (C) 2014 Elsevier B.V. All rights reserved.

DOI 

10.1016/j.jnucmat.2014.03.031

Dislocation mechanism of deuterium retention in tungsten under plasma implantation

V. Dubinko, D. Terentyev, P. Grigorev, A. Bakaev, G. Van Oost, F. Gao, D. Van Neck, E. Zhurkin
Journal of Physics: Condensed Matter
26, 395001
2014
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Abstract 

We have developed a new theoretical model for deuterium (D) retention in tungsten-based alloys on the basis of its being trapped at dislocations and transported to the surface via the dislocation network with parameters determined by ab initio calculations. The model is used to explain experimentally observed trends of D retention under sub-threshold implantation, which does not produce stable lattice defects to act as traps for D in conventional models. Saturation of D retention with implantation dose and effects due to alloying of tungsten with, e.g. tantalum, are evaluated, and comparison of the model predictions with experimental observations under high-flux plasma implantation conditions is presented.

Hardening due to dislocation loop damage in RPV model alloys: role of Mn segregation

D. Terentyev, X. He, G. Bonny, A. Bakaev, E. Zhurkin, L. Malerba
Journal of Nuclear Materials
457, 173–181
2015
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Abstract 

The exact nature of the radiation defects causing hardening in reactor vessel pressure steels at high doses is not yet clearly determined. While generally it is attributed to solute-rich clusters (precipitates) and point defects clusters (matrix damage), recent fine-scale experiments and atomistic simulations suggest that solute rich clusters, mainly containing Mn, Ni and Cu, might be the result of the segregation of these elements to small dislocation loops (heterogeneous nucleation), so that the distinction between precipitates and matrix damage becomes blurred. Here, we perform an atomistic study to investigate the interaction of a0/2〈1 1 1〉 dislocation loops with moving dislocations and specifically address the effect of solute segregation on the loop’s strength and interaction mechanism, focusing in particular on Mn, alone or with other crucial solute elements such as Cu and Ni. It is found that the enrichment of Mn in the core of dislocation loops causes significant increase of the unpinning stress, especially for small, invisible ones. At the same time, the solute segregation at the dislocation loops enhances their resistance against absorption by moving dislocations.

Energetic stability of solute-carbon-vacancy complexes in bcc iron

A. Bakaev, D. Terentyev, E. Zhurkin, D. Van Neck
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms
352, 47-50
2015
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Abstract 

The strong binding between a vacancy and carbon in bcc iron plays an important role in the evolution of radiation-induced microstructure. Our previous ab initio study points to the fact that the vacancy-carbon (V-C) pair can serve as a nucleus for the solute-rich clusters. Here, we continue the ab initio study by considering the interaction of mixed solute clusters (Mn, Ni and Si) with the V-C pair, and the interaction of typical alloying elements of Fe-based steels (i.e., Mn, Ni, Cu, Si, Cr and P) with di-carbon-vacancy pair (V-C-2). We have identified the sequence of growth of Ni, Si and Mn solute-rich clusters nucleating on the V-C pair. The mixed-solute-V-C configurations are found to be less stable clusters than pure-solute-V-C clusters with the energy difference up to 0.22 eV per four atoms. The V-C-2 pair is found to be as strong nucleation site for the solute-rich clusters as the V-C pair. Only Si solute atom stands out from the trend showing a weaker affinity to the V-C-2 complex by 0.09 eV compared to the attraction to the V-C pair. The overall results point to the importance of taking into account the existence of both V-C and V-C-2 complexes in studying the formation of solute-rich clusters in Fe-based steels for nuclear applications. (C) 2014 Elsevier B.V. All rights reserved.

Atomistic simulation of the interaction between mobile edge dislocations and radiation-induced defects in Fe-Ni-Cr austenitic alloys

A. Bakaev, D. Terentyev, P. Grigorev, E. Zhurkin
JOURNAL OF SURFACE INVESTIGATION-X-RAY SYNCHROTRON AND NEUTRON TECHNIQUES
8 (2), 220-228
2014
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Abstract 

The classical molecular dynamics method is employed to simulate the interaction of edge dislocations with interstitial Frank loops (2 and 5 nm in diameter) in the Fe-Ni10-Cr20 model alloy at the temperatures T = 300–900 K. The examined Frank loops are typical extended radiation-induced defects in austenitic steels adapted to nuclear reactors, while the chosen triple alloy (Fe-Ni10-Cr20) has the alloying element concentration maximally resembling these steels. The dislocation-defect interaction mechanisms are ascertained and classified, and their comparison with the previously published data concerning screw dislocations is carried out. The detachment stress needed for a dislocation to overcome the defect acting as an obstacle is calculated depending on the material temperature, defect size, and interaction geometry. It is revealed that edge dislocations more efficiently absorb small loops than screw ones. It is demonstrated that, in the case of small loops, the number of reactions accompanied by loop absorption increases with temperature upon interaction with both edge and screw dislocations. It is established that Frank loops are stronger obstacles to the movement of screw dislocations than to the movement of edge ones.

Carbon-vacancy interaction controls lattice damage recovery in Iron

D. Terentyev, K. Heinola, A. Bakaev, E. Zhurkin
Scripta Materialia
86, 9-12
2014
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Abstract 

Ab initio techniques are applied to assess the positron lifetime of carbon–vacancy (C–V) complexes in iron for the first time. Positron lifetime is extremely sensitive to C–V arrangement and multiplicity. Following the ab initio lifetime data, a C–V complex can be detected as a single or clustered vacancy, or remain indistinguishable from bulk. Combining ab initio data with kinetic rate theory, we modelled annealing of irradiated Fe–C alloys and performed one-to-one comparison with experiment, which revealed a good agreement.

Deuterium accumulation in tungsten under low-energy high-flux plasma exposure

P. Grigorev, V. Dubinko, D. Terentyev, A. Bakaev, E. Zhurkin
JOURNAL OF SURFACE INVESTIGATION-X-RAY SYNCHROTRON AND NEUTRON TECHNIQUES
8 (2), 234–238
2014
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Abstract 

The accumulation of deuterium implanted in tungsten is simulated within the framework of kinetic diffusion theory. The influence of the tungsten microstructure (dislocation density and impurity concentration) on the process of deuterium capture and accumulation is considered. It is established that, under the chosen irradiation conditions, deuterium accumulation in the near-surface region is determined by capture at defects formed during implantation. The deuterium concentration gradient, together with the material microstructure, determines its accumulation in tungsten. Variation in the dislocation density and impurity concentration does not affect the simulation results, which is, first, related to the fact that the model used does not contain alternative mechanisms for the formation and growth of vacancy clusters under the subthreshold irradiation mode. The simulation results are compared with experimental data, and ways of improving the model are discussed in order to explain the deuterium-saturation effect for high fluences (more than 1023 m−2).

Molecular 7 dynamics simulation of the interaction of dislocations with radiation-induced defects in Fe-Ni-Cr austenitic alloys

A. Bakaev, D. Terentyev, E. Zhurkin, P. Grigorev
JOURNAL OF SURFACE INVESTIGATION-X-RAY SYNCHROTRON AND NEUTRON TECHNIQUES
7 (2), 211-217
2013
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Abstract 

A classical molecular dynamics method is used to theoretically study the interaction of dislocations with typical radiation-induced defects in an Fe-Ni10-Cr20 austenitic alloy. As a result, a set of interactions and the corresponding values for the critical stress required for unpinning of a dislocation from an obstacle are obtained for different temperatures and interaction geometries.

On the thermal stability of late blooming phases in reactor pressure vessel steels: An atomistic study

G. Bonny, D. Terentyev, A. Bakaev, E. Zhurkin, M. Hou, L. Malerba
Journal of Nuclear Materials
442 (1-3), 282–291
2013
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Abstract 

Radiation-induced embrittlement of bainitic steels is the lifetime limiting factor of reactor pressure vessels in existing nuclear light water reactors. The primary mechanism of embrittlement is the obstruction of dislocation motion produced by nanometric defect structures that develop in the bulk of the material due to irradiation. In view of improving the predictive capability of existing models it is necessary to understand better the mechanisms leading to the formation of these defects, amongst which the so-called “late blooming phases”. In this work we study the stability of the latter by means of density functional theory (DFT) calculations and Monte Carlo simulations based on a here developed quaternary FeCuNiMn interatomic potential. The potential is based on extensive DFT and experimental data. The reference DFT data on solute–solute interaction reveal that, while Mn–Ni pairs and triplets are unstable, larger clusters are kept together by attractive binding energy. The NiMnCu synergy is found to increase the temperature range of stability of solute atom precipitates in Fe significantly as compared to binary FeNi and FeMn alloys. This allows for thermodynamically stable phases close to reactor temperature, the range of stability being, however, very sensitive to composition.

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