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Simulation of radiation damage in Fe and Fe-Cr
KTH, School of Engineering Sciences (SCI), Physics.
2005 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

Steel is an important structural material in nuclear reactors used for example in pressure vessels and fast reactor cladding. In reactor environments it has been observed that ferritic steels are more resistant to swelling than the austenitic steels typically used. Much effort has been put into developing basic models of FeCr alloys which can serve as model alloys for describing ferritic steels. As a result, a number of interatomic potentials for Fe and FeCr alloys exist today.

For the work in this thesis, basic material properties coming from experiments or ab initio calculations were used to fit interatomic potentials for Fe, Cr and FeCr implementing both the embedded atom method and the Finnis-Sinclair formalisms. The potentials were then validated by molecular dynamic calculations of material properties such as defect formation energies, migration energies and thermal expansion. Further studies of potential performance were carried out in simulations of radiation damage cascades and thermal aging.

The influence of the interatomic potential on the primary defect state in materials under irradiation was analyzed in a study comparing results obtained using four different potentials. The objective of the study was to find correlations between potential properties and the primary damage state produced in simulations of displacement cascades. The defect evolution and clustering during different cascade stages were also investigated to try to gain a better understanding of these processes.

Place, publisher, year, edition, pages
Stockholm: KTH , 2005. , 38 p.
Series
Trita-FYS, ISSN 0280-316X ; 20005:61
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-503ISBN: 91-7178-198-6 (print)OAI: oai:DiVA.org:kth-503DiVA: diva2:14246
Presentation
2005-11-25, Sal FR4, AlbaNova, Roslagstullsbacken 21, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20101208Available from: 2005-11-23 Created: 2005-11-23 Last updated: 2010-12-08Bibliographically approved
List of papers
1. Modeling of chromium precipitation in Fe-Cr alloys
Open this publication in new window or tab >>Modeling of chromium precipitation in Fe-Cr alloys
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2004 (English)In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 69, 094103- p.Article in journal (Refereed) Published
Abstract [en]

We have implemented a set of Embedded Atom Method (EAM) potentials for simulation of Fe-Cr alloys. The functions for the pure elements were fitted to the respective elastic constants, vacancy formation energy, and thermal expansion coefficients. For Cr, properties of the paramagnetic state were applied, providing a positive Cauchy pressure and hence applicability of the EAM. By relaxing the requirement of reproducing the pressure-volume relation at short interaction distances, stability of the <110> self-interstitial could be obtained. Our Fe-potential gives E-<110>(f)-E-<111>(f)=-0.23 eV. Mixed Fe-Cr pair potentials were fitted to the calculated mixing enthalpy of ferromagnetic Fe-Cr, which is negative for Cr concentrations below 6%. Simulation of thermal aging in Fe-Cr alloys using a potential fitted to the mixing enthalpy of Fe-20Cr exhibited pronounced Cr-precipitation for temperatures below 900 K, in agreement with the phase diagram. No such ordering was observed at any temperature using a potential fitted to the mixing enthalpy of Fe-5Cr. Applied to recoil cascade simulations the new potentials predict a smaller number of surviving defects than potentials found in the literature. We obtain a cascade efficiency of 0.135 NRT for damage energies inbetween 10 and 20 keV. An enhanced probability for Cr atoms to end up in defect structures is observed.

Keyword
computer-simulation, alpha-iron, elastic-constants, transition-metals, bcc iron, defect, irradiation, steels, decomposition, temperature
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-8805 (URN)10.1103/PhysRevB.69.094103 (DOI)000220812800036 ()2-s2.0-2142771770 (Scopus ID)
Note

QC 20101208

Available from: 2005-11-23 Created: 2005-11-23 Last updated: 2017-12-14Bibliographically approved
2. Relation between thermal expansion and interstitial formation energy in Fe and Cr
Open this publication in new window or tab >>Relation between thermal expansion and interstitial formation energy in Fe and Cr
2005 (English)In: NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS, Amsterdam: ELSEVIER , 2005, Vol. 228, 122-125 p.Conference paper, Published paper (Refereed)
Abstract [en]

By fitting a potential of modified Finnis-Sinclair type to the thermal expansion of ferromagnetic Fe and paramagnetic Cr, stability of the (I 10) self-interstitial atom is obtained. The resulting potentials are relatively hard, yielding high SIA formation energies. Less hard potentials give lower interstitial formation energy, but predict too small thermal expansion. We also show that the formation energy of the (I 11) SIA depends on distances in-between the 2nd and 3rd neighbour. By raising the value of the pair potential in this region, the energy difference with respect to the (110) configuration calculated with VASP in the PAW approximation can be reproduced.

Place, publisher, year, edition, pages
Amsterdam: ELSEVIER, 2005
Series
Nuclear instruments & methods in physics research section b-beam interactions with materials and atoms, ISSN 0168-583X
Keyword
Finnis-Sinclair potential, iron, chromium, thermal expansion
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-8806 (URN)10.1016/j.nimb.2004.10.032 (DOI)000226669800020 ()2-s2.0-11344289838 (Scopus ID)
Conference
7th International Conference on Computer Simulation of Radiation Effects in Solids Helsinki, FINLAND, JUN 28-JUL 02, 2004
Note

QC 20101208

Available from: 2005-11-23 Created: 2005-11-23 Last updated: 2016-04-19Bibliographically approved
3. Effect of the interatomic potential on the features of displacement cascades in alpha-Fe: A molecular dynamics study
Open this publication in new window or tab >>Effect of the interatomic potential on the features of displacement cascades in alpha-Fe: A molecular dynamics study
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2006 (English)In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 351, no 03-jan, 65-77 p.Article in journal (Refereed) Published
Abstract [en]

The primary state of damage obtained in molecular dynamics (MD) simulations of displacement cascades in alpha-Fe, particularly the fraction of point-defects in clusters, depends on the interatomic potential used to describe the atomic interactions. The differences may influence the microstructural evolution predicted in damage accumulation models which use results from MD cascade simulations as input. In this work, a number of displacement cascades of energy ranging from 5 to 40 keV have been simulated using the same procedure with four different interatomic potentials for alpha-Fe, each of them providing, among other things, varying descriptions of self-interstitial atoms (SIA) in this metal. The behaviour of the cascades at their different phases and the final surviving defect population have been studied and compared applying the same cascade analysis criteria for all potentials. The outcome is discussed trying to identify the characteristics of the potential that have the largest influence on the predicted primary state of damage.

Keyword
defect production, positron-annihilation, computer-simulation, thermal-equilibrium, collision cascades, vacancy formation, cluster formation, iron, metals, damage
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-15781 (URN)10.1016/j.jnucmat.2006.02.020 (DOI)000238620600008 ()2-s2.0-33746569552 (Scopus ID)
Conference
Conference: Symposium on Microstructural Processes in Irradiated Materials held at the Annual Meeting of the Minerals-Metals-and-Materials-Society. San Francisco, CA. FEB 14-17, 2005
Note

QC 20100525 QC 20111004.

Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
4. Cluster formation mechanisms during relaxation and post-relaxation cascade stages in α-Fe:: a molecular dynamics study
Open this publication in new window or tab >>Cluster formation mechanisms during relaxation and post-relaxation cascade stages in α-Fe:: a molecular dynamics study
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(English)Article in journal (Other academic) Submitted
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-8808 (URN)
Note
QS 20120328Available from: 2005-11-23 Created: 2005-11-23 Last updated: 2012-03-28Bibliographically approved

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