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Multiscale modelling of radiation-enhanced diffusion phenomena in metals
KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
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: urn:nbn:se:kth:diva-163279ISBN: 978-91-7595-495-0 (print)OAI: oai:DiVA.org:kth-163279DiVA: diva2:799524
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
List of papers
1. Modeling of the magnetic free energy of self-diusion in bcc Fe
Open this publication in new window or tab >>Modeling of the magnetic free energy of self-diusion in bcc Fe
(English)Manuscript (preprint) (Other academic)
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-163294 (URN)
Note

to be submitted to Physical review B. QS 2015

Available from: 2015-03-31 Created: 2015-03-31 Last updated: 2015-04-01Bibliographically approved
2. Dislocation bias factors in fcc copper derived from atomistic calculations
Open this publication in new window or tab >>Dislocation bias factors in fcc copper derived from atomistic calculations
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
Keyword
Atomistic calculations, Bias factor, Dislocation densities, Elasticity theory, Interaction energies, Model-based OPC
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-122390 (URN)10.1016/j.jnucmat.2013.06.029 (DOI)000325447600046 ()2-s2.0-84880375938 (Scopus ID)
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
3. Anomalous bias factors of dislocations in bcc iron
Open this publication in new window or tab >>Anomalous bias factors of dislocations in bcc iron
Show others...
2015 (English)In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 461, 221-229 p.Article in journal (Refereed) Published
Abstract [en]

Dislocation bias factors in bcc Fe have been calculated based on atomistic interaction energy maps on three kinds of dislocations, namely the a0/2〈1 1 1〉{1 1 0} screw, a0/2〈1 1 1〉{1 1 0} and a0〈1 0 0〉{0 0 1} edge dislocations. The results show that the dislocation bias is higher for the a0/2〈1 1 1〉 edge dislocation than for the a0〈1 0 0〉 edge dislocation, even though the latter possesses a larger Burgers vector. This indicates the importance of the dislocation core contribution. For the a0/2〈1 1 1〉{1 1 0} screw dislocation, a negative dislocation bias has been obtained, which implies a more efficient absorption of vacancies than of SIAs. The effect of coexistence of both edge- and screw dislocations are assessed by a total bias. A possible complementary mechanism for explaining the long swelling incubation time in bcc metals is suggested and discussed.

Place, publisher, year, edition, pages
Elsevier, 2015
Keyword
Screw dislocations, Screws, Atomistic interactions, Bcc iron, Bcc metals, Bias factor, Complementary mechanisms, Dislocation core, Edge and screw dislocations, Incubation time
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-163276 (URN)10.1016/j.jnucmat.2015.03.025 (DOI)000355023900030 ()2-s2.0-84925678083 (Scopus ID)
Funder
EU, FP7, Seventh Framework Programme, (MatISSE project) 604862
Note

QC 20150331

Available from: 2015-03-31 Created: 2015-03-31 Last updated: 2017-12-04Bibliographically approved
4. Dislocation bias calculations in fcc materials
Open this publication in new window or tab >>Dislocation bias calculations in fcc materials
(English)Manuscript (preprint) (Other academic)
Identifiers
urn:nbn:se:kth:diva-163397 (URN)
Note

QS 2015

Available from: 2015-04-01 Created: 2015-04-01 Last updated: 2015-04-01Bibliographically approved
5. Electron irradiation accelerated Cu precipitation in cast iron and an FeCu model alloy
Open this publication in new window or tab >>Electron irradiation accelerated Cu precipitation in cast iron and an FeCu model alloy
Show others...
(English)Manuscript (preprint) (Other academic)
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-163403 (URN)
Note

QS 2015

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

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