Center for Molecular Modeling - L. Malerba

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

alex — Tue, 19 Aug 2014 11:52:43 +0000

D. Terentyev, X. He, G. Bonny, A. Bakaev, E. Zhurkin, L. Malerba

Journal of Nuclear Materials

457, 173–181

2015

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.

DOI

http://dx.doi.org/10.1016/j.jnucmat.2014.11.023

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15_j_nucl_phys_457(2015)173_Terentyev.pdf

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

alex — Tue, 19 Aug 2014 11:30:13 +0000

G. Bonny, D. Terentyev, A. Bakaev, E. Zhurkin, M. Hou, L. Malerba

Journal of Nuclear Materials

442 (1-3), 282–291

2013

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.

DOI

http://dx.doi.org/10.1016/j.jnucmat.2013.08.018

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13_jnuclmat_442(1-3)282_Bonny.pdf

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

wim — Mon, 03 Oct 2011 10:31:42 +0000

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

Physical Review B

79 (10), 104207

2009

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.

DOI

http://dx.doi.org/10.1103/PhysRevB.79.104207

Private attachment

09 phys. rev. B 79(10)104207 bonny.pdf

Ab initio study of basic properties of minor alloying elements in high-Cr ferritic steels

alex — Tue, 19 Aug 2014 12:40:22 +0000

A. Bakaev, L. Malerba

ISBN/ISSN:

Talk

Conference / event / venue

4th n-FAME and 22nd Fe-Cr alloys workshop

Edinburgh, Scotland

Tuesday, 4 June, 2013 to Wednesday, 5 June, 2013

FWO D. Van Neck - SCK.CEN (3G007109)

wim — Wed, 15 May 2013 08:55:34 +0000

Project promotor

D. Van Neck, L. Malerba

Financierende instantie

FWO

Project data

01/10/2009 to 31/12/2014

Bedrag

€134 000,00

Project titel

Development of interatomic potentials for ternary iron-based alloys

Personeel

A. Bakaev

Project ref.

FWO D. Van Neck (3G007109) B/10069/*

FWO 3G007109 (DVN/SCK)

wim — Tue, 04 Oct 2011 07:20:16 +0000

SAP ref.

B/10069/*

Promotor(s)

D. Van Neck, L. Malerba

Description

Ontwikkeling van interatomaire potentialen voor ternaire Fe-gebaseerde legeringen toepasbaar in de studie van stralingseffecten, op basis van dichtheidsfunctionaaltheorie en consistent met het thermodynamische gedrag.

Attachments (ZAP restricted field)

contract G007109N.pdf