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Dislocation bias factors in fcc copper derived from atomistic calculations
KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.ORCID iD: 0000-0002-2381-3309
KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
2013 (English)In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 441, no 1-3, 357-363 p.Article in journal (Refereed) Published
Abstract [en]

Atomistic calculations were employed in order to calculate the interaction energy of an edge dislocation with different point defects. The bias factor was calculated by applying a finite element method on the interaction energy landscapes obtained from the atomistic calculations. A comparison of the calculated bias factor with a model based on elasticity theory reveals around 30% discrepancy under conditions representative for electron irradiation at 600 degrees C. Possible reasons are discussed. The bias factor dependence on dislocation density and ambient temperature is presented and discussed.

Place, publisher, year, edition, pages
Elsevier, 2013. Vol. 441, no 1-3, 357-363 p.
Keyword [en]
Atomistic calculations, Bias factor, Dislocation densities, Elasticity theory, Interaction energies, Model-based OPC
National Category
Atom and Molecular Physics and Optics
Identifiers
URN: urn:nbn:se:kth:diva-122390DOI: 10.1016/j.jnucmat.2013.06.029ISI: 000325447600046Scopus ID: 2-s2.0-84880375938OAI: oai:DiVA.org:kth-122390DiVA: diva2:622099
Projects
Generation IV reactor research and development (GENIUS)
Note

QC 20130718

Available from: 2013-05-20 Created: 2013-05-20 Last updated: 2017-12-06Bibliographically approved
In thesis
1. Modelling of Dislocation Bias in FCC Materials
Open this publication in new window or tab >>Modelling of Dislocation Bias in FCC Materials
2013 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Irradiation induced void swelling is problematic for the application of austenitic steels under high dose irradiation. In this thesis, the swelling is characterized by dislocation bias. The dislocation bias is obtained using the finite element method, accounting for fcc copper and nickel under electron irradiation. The methodology is implemented with the interaction energies between an edge dislocation and point defects. Analytically derived interaction energies, which are based on elasticity theory, are compared with interaction energies obtained from atomistic model using semi-empirical atomic potentials as physics basis. The comparison shows that the description of analytical interaction energies is inaccurate in the dislocation core regions. The bias factor dependence on dislocation density and temperature is presented and discussed. At high temperatures or low dislocation densities, the two approaches tend to converge. However, the dislocation bias based on the interaction energies from the two approaches, reveals larger discrepancy for nickel than for copper. The impact on dislocation bias from the different stacking fault energies of copper and nickel is elaborated. Nickel, which has a larger stacking fault energy, is predicted to have larger swelling rate than copper under the same irradiation conditions.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. viii, 33 p.
Series
Trita-FYS, ISSN 0280-316X ; 2013:20
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-122407 (URN)978-91-7501-785-3 (ISBN)
Presentation
2013-06-12, FA31, Roslagstullsbacken 21, Stockholm, 10:15 (English)
Opponent
Supervisors
Note

QC 20130530

Available from: 2013-05-30 Created: 2013-05-20 Last updated: 2013-06-25Bibliographically approved
2. Multiscale modelling of radiation-enhanced diffusion phenomena in metals
Open this publication in new window or tab >>Multiscale modelling of radiation-enhanced diffusion phenomena in metals
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

A multiscale modelling framework and an experiment campaign are used to study void swelling and Cu precipitation under irradiation. Several aspects regarding defect and solute diffusion under irradiation have been studied in this thesis.

First, a self-diffusion model in bcc Fe has been constructed in order to describe the non-linear effects, especially the magnetic transition, around the Curie temperature. First principles calculations are applied to obtain the parameters in the model. The paramagnetic state is simulated by statistical sampling of randomly arranged spin states on each atom. The model fits well with the experimental observations.

Then, a combination of atomistic calculations and the finite element method (FEM) is developed in order to solve the diffusion equations of point defects, which are under the influence of a dislocation strain field. The dislocation bias, a key parameter in void swelling models, is hence obtained numerically. The method has been applied in different structural lattices. In the bcc materials, anomalous bias factors have been found for both edge- and screw dislocations. For the edge dislocations, the traditional assumption that the dislocation bias value is proportional to the Burgers vector has been proven not appropriate. For the screw dislocation, a negative bias value is obtained. This implies that vacancies, instead of self-interstitials, are preferentially absorbed into the screw dislocations. Thus a possible complementary mechanism is here introduced for explaining the long swelling incubation time before the steady swelling in bcc materials compared to that in fcc materials.

Edge dislocations in fcc materials split into partial dislocations due to their  relatively low stacking fault energy. This feature complicates the analytical derivation of the dislocation bias. However, by transforming the analytical dislocation-point defect interaction energies to discrete interaction maps numerically applied in the FEM method, it is possible to perform a systematic study on typical fcc materials, i.e. Cu, Ni and Al. The impacts on the dislocation bias from elastic constants and stacking fault energy have been studied. It is found that the partial splitting distance is the dominating factor that determines the dislocation bias. A prediction method has been hence developed to obtain the dislocation bias of the austenitic alloys, for which it is difficult to use an atomistic description of the interaction maps. A prediction of about 8% dislocation bias of a typical austenitic 316 alloy has been made without performing specific atomistic calculations in the austenitic alloys.

Finally, Cu precipitation under irradiation has been studied using both experiment and simulations. Cast iron and FeCu alloy samples were irradiated for a week with 2 MeV electrons. The resistivity of the samples was measured in situ. The microstructure of the samples was then examined by atom probe tomography. No Cu precipitation was found in the cast iron sample while small Cu clusters are observed in the FeCu model alloy. To simulate the clustering process, Kinetic Monte Carlo (KMC) and rate theory methods are used. Both the KMC and rate theory simulations show clearly the Cu clustering process in the FeCu alloy but not in cast iron within the irradiation dose.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. x, 59 p.
Series
TRITA-FYS, ISSN 0280-316X ; 2015:16
National Category
Metallurgy and Metallic Materials
Research subject
Materials Science and Engineering
Identifiers
urn:nbn:se:kth:diva-163279 (URN)978-91-7595-495-0 (ISBN)
Public defence
2015-04-24, Sal F3, Lindstedtsvägen 26, KTH, Stockholm, 09:30 (English)
Opponent
Supervisors
Note

QC 20150401

Available from: 2015-04-01 Created: 2015-03-31 Last updated: 2015-04-01Bibliographically approved

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