Elsevier

Acta Materialia

Volume 180, November 2019, Pages 141-148
Acta Materialia

Rearrangement of interstitial defects in alpha-Fe under extreme condition

https://doi.org/10.1016/j.actamat.2019.09.007Get rights and content

Abstract

In this study, by theoretical means, we reveal the main mechanisms that underpin the microstructure evolution driven by the formation of self-interstitial atoms (SIAs) clusters in body centered cubic iron under extreme conditions. Using Frenkel pairs accumulation simulations we point the complex interplay between the two families of interstitial defects, the dislocation loops with Burgers vectors <100> and ½<111> and the tridimensional C15 clusters. We reconcile the previous sparse understanding of microstructure evolution that put in opposition various mechanisms of defects formation by showing that both ½ <111> loops self-interactions and C15 clusters transformations produce <100> loops. Moreover, we exhibit the fact that these tri-dimensional clusters can form under irradiations with only the Frenkel pair accumulation that mimics electron irradiation and not only in high-energy cascades as it was previously stated. Finally, we show that the tridimensional C15 clusters even precede production of loops under irradiation.

Section snippets

Introduction: 2D and 3D defects in irradiated bcc-iron

The performance of materials under extreme conditions is driven by the formation and the mobility of clusters of vacancies and interstitial atoms. Vacancies and self-interstitial atoms (SIAs) form either two or three-dimensional clusters depending on their sizes and mainly because of the competition between the interface and the bulk energies. In body centered cubic (bcc) metals, the clusters of vacancy behave similarly [1], while the SIAs clusters underlay complex energetic landscape with

Methodology: Frenkel pairs accumulation

We perform all our molecular dynamics simulations using the LAMMPS code [42] with the M07 EAM potential for iron [14,43]. This potential has the particularity of satisfactory reproducing relative formation energies of small loops with respect to C15 clusters, in agreement with 0 K ab initio calculations [6,14]. We design two sets of simulations: the first set explores the entire process of nucleation and growth of defect clusters and/or loops by irradiation while the second one targets the

Results: nucleation and transformation of C15 clusters

We start with the analysis of the first set of simulations where we apply the FPA methodology. We report evolutions of dislocation densities and C15 sizes with dose (dpa) on Fig. 1 and on Fig. 2, respectively, for small and big supercells. We note that evolutions of densities of dislocations as well as number and size of C15 clusters behave identically with dose for both sizes of supercell. In addition, evolution of microstructures look very similar too, as illustrated on snapshots at different

Discussion: <100> loops nucleate from C15 clusters and ½ <111> loops

Our simulations suggest that the response of iron to irradiations can be decomposed into different stages. We have identified the following ones: (i) production of point defects by irradiation; (ii) their transformation into C15 clusters; then (iii) nucleation of ½ <111> loops (from C15 clusters) and; subsequently (iv) of <100> loops (from C15 clusters and ½<111> loops); finally (v) stabilization of a steady state in which all types of defects are present. Besides this sequence itself, some new

Conclusion

In the present work, we intensively use molecular dynamics simulations to investigate the response of iron to irradiation. For this purpose, we used the Frenkel pairs accumulation framework whose main characteristic is an accelerated introduction of damages. With these simulations, we expect to mimic reliably electron irradiation of iron at low temperature, knowing that thermal – i.e. long-range – diffusion is overlooked.

In such conditions, we find a complex interplay between the two main

Acknowledgments

This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euroatom research and training program 2014–2018 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission. The research leading to these results is partly funded by the European Atomic Energy Community’s (Euratom) Seventh Framework Programme FP7/2007–2013 under grant agreement No. 604862 (MatISSE project)

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