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Energy barriers for carbon diffusion in ferrite under heterogeneous stress


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International workshop on multiscale simulation of the prediction of radiation damage in reactor pressure vessel steel and internals up to 60 years of operation / 10-12 décembre 2013, Fontainebleau (France)

Type de document > *Congrès/colloque

Mots clés >

Unité de recherche > IRSN/PSN-RES/SEMIA/LPTM, IRSN/PSN-RES/SAG/LETR

Auteurs > TCHITCHEKOVA Deyana, MORTHOMAS Julien, RIBEIRO Fabienne, DUCHER Roland, PEREZ Michel

Date de publication > 10/12/2013

Résumé

The context and objectives are :

  • The diffusion of carbon in iron controls the kinetics of many transformations in steels(such as, cementite precipitation, martensite ageing, massive austenite-ferrite transformation and bainite formation).
  • Diffusion of carbon in defect-free ferrite (the body-centred cubic structure of iron): a fairly well known mechanism, extensively studied and characterized.
  • When other defects are present: both the diffusion mechanism and its kinetics are affected. Case of dislocations: they create very large and non-uniform stresses, inducing important effects on the energy barrier of impurities.
  • Diffusion and segregation of interstitial carbon to dislocations introduced by plastic deformation in ferritic iron: leads to the growth of so-called Cottrell atmospheres around the dislocations (responsible for static strain aging in ferritic steels).
  • In this work, the effect of an heterogeneous stress field on diffusion energy barriers is adressed: a novel method, called LinCoSS (Linear Combination of Stress States), which is very fast and easy to implement alternative to existing approaches [1].
  • Atomistic simulations provide a good alternative for studying the diffusion processes in the presence of stress: 1/Molecular dynamics (MD): could serve as a perfect framework if not so limited in simulation time span (typically, a few ns). 2/ Atomistic Kinetic Monte-Carlo (aKMC) method: very well adapted for studying the diffusion of atomic species, based on knowledge of the different escape pathways and the corresponding escape rates.
  • The impact of the stress field induced by the presence of a defect on the energy barriers cannot be neglected, and need to be quantitatively accounted for.

  • In this work, the effect of an heterogeneous stress field on diffusion energy barriers is adressed: a novel method, called LinCoSS (Linear Combination of Stress States), which is very fast and easy to implement alternative to existing approaches.