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Microstructure Evolution of FeCr Alloys under Neutron and Ion Irradiation

This study investigates the microstructure evolution of FeCr alloys under neutron and ion irradiation using transmission electron microscopy (TEM). The aim is to obtain a complete description of the nanostructure and its evolution, which will further validate simulation methods. Various characterization techniques such as PAS, TEM, SANS, APT, and EXAFS are applied to detect defects, dislocation loops, voids, precipitates, and solute redistribution. The methodology includes neutron and ion irradiation experiments on FeCr binary model alloys and analysis of the influence of different variables on microstructural damage evolution.

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Microstructure Evolution of FeCr Alloys under Neutron and Ion Irradiation

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  1. M. Hernández Mayoral, Division of Structural Materials, CIEMAT Transmission Electron Microscopy (TEM) investigation of the microstructure evolution under neutron and ion irradiation of FeCr alloys M. Hernández-Mayoral Division of Structural Materials Department of Technology CIEMAT, Spain 22nd Workshop on Iron-Chromium Alloys and 4th Workshop on nuclear Fe alloys: modelling and experiments Edinburgh, UK 4-5 June, 2013

  2. Contents • Context of the work • Experimental methodology • Characterisation techniques • Materials • Irradiation experiments • Ion irradiation • Neutron irradiation • Microstructural characterisation by TEM • Results from ion irradiated materials • Results from neutron irradiated materials • Summary and conclusions M. Hernández Mayoral, Division of Structural Materials, CIEMAT

  3. Context of the work • GETMAT (GenIV and Transmutation MATerials) • This project deals with the study of candidate materials for the fabrication of Generation IV and transmutation systems. Amongst others, priorities of the project are: • Improvement and extension of 9-12 F/M steels qualification • ODS alloys development and characterisation • Improved modeling and experimental validation • Project Structure • WP1: Metallurgical and mechanical behavior of ODS steels • WP2: Material compatibility with coolant • WP3: Irradiation behavior of structural materials • WP4: Multiscale modelling and model experiments • Task 4.1: Modelling of fundamental properties of Fe and FeCr alloys • Task 4.2: Modelling of radiation effects in Fe and FeCr alloys • Task 4.3: Modelling-oriented experiments in Fe and FeCr alloys M. Hernández Mayoral, Division of Structural Materials, CIEMAT

  4. Objective Task 4.3: Modelling-oriented experiments in Fe and FeCr alloys • The aim of the work is to obtain a complete description of the nanostructure and its evolution in FeCr alloys under irradiation • Microstructural changes are the origin of changes on mechanical properties • The information obtained will be suitable for the further validation of simulation methods which are being developed in parallel within the project. • The approach we are following is: • Materials under study: FeCr binary model alloys • Irradiation experiments: • Neutron irradiation • Ion irradiation • Microstructural characterisation applying as many techniques as possible • Influence of different variables on microstructural damage evolution • Comparison of the ion and neutron irradiation effect M. Hernández Mayoral, Division of Structural Materials, CIEMAT

  5. Characterization techniques • Different advanced materials characterisation techniques are applied: PAS, TEM, SANS, APT and EXAFS. • Positron Annihilation Spectroscopy (PAS): • SCK, CEMHTI, U. Chalmers • detection of vacancy type defects • Transmission Electron Microscopy (TEM): • CIEMAT • Detection of dislocation loops, voids, precipitates • Small Angle Neutron Scattering (SANS): • HZDR • Precipitates, voids • Atom Probe Tomography (APT): • U. Rouen • Solute redistribution • Extended X-ray Absorption Fine Structure (EXAFS): • PSI • Local atomic environment  The complementarity of the techniques and the combination of their results provide a full picture of the nanostructure induced by irradiation as each of them is sensitive to different aspects of the irradiation damage. M. Hernández Mayoral, Division of Structural Materials, CIEMAT

  6. All the investigation is being performed on the same set of materials MIRE-Cr Program carried out by SCK-CEN 4 model FeCr binary alloys: 2.36 (2.5), 4.62 (5), 8.39 (9), 11.62 (12) %Cr; Industrial purity 1050ºC, 1 h in high vacuum for austenitization and stabilisation+ tempering at 730ºC, 4 h (AC) Optical microscopy indicate ferritic/martensitic microstructures with ferrite fractions decreasing at increasing Cr content Experimental methodology: Materials

  7. Unirradiated material 2.5 at% Cr 5 at% Cr 12 at% Cr 9 at% Cr Courtesy of C.Heintze (HZDR) Differentinitialmicrostructuresdependingonthe Cr content Fromferritictoferritic-martensiticmicrostructure as Cr increases C distributionfrom IF and MAE: homogeneous in thematrixfor Fe2.5Cr, while at boundariesfortheother Cr contentalloys

  8. Neutron irradiated material PAS (SCK-CEN) TEM (CIEMAT) SANS (HZDR) APT (Univ. Rouen) Effect of: Cr content Dose (0.06, 0.6 and 1.5 dpa) Ion irradiated material PAS (CEMHTI and Univ Chalmers) TEM (CIEMAT) Synchrotron techniques (EXAFS, XMCD, XRD)(PSI) APT (Univ. Rouen) Effect of: Cr content Dose (1 and 5 dpa) Irradiation temperature (100, 300 and 420ºC) Summarising the methodology Materials: The same set of four FeCr model alloys for all the irradiation experiments and characterisation techniques M. Hernández Mayoral, Division of Structural Materials, CIEMAT

  9. Ion irradiated materials:characterisation by TEM M. Hernández Mayoral, Division of Structural Materials, CIEMAT

  10. Ion irradiated materials characterization SRIM calculation profile • Ion irradiation at the Ion Beam Centre at HZDR (Germany). • Energy of the Fe ions: 5, 2 and 0.5 MeV) to induce a flat damage profile (about 1.3 µm) • at different temperatures (100, 300 and 420ºC) • Doses: 1 and 5 dpa • Flux: 2x10-4 dpa/s Acknowledgment: "This work has been supported by the European Community as an Integrating Activity 'Support of Public and Industrial Research Using Ion Beam Technology (SPIRIT)' under EC contract no. 227012." 3MeV Tandetron (AIM,-HZDR (Germany)) M. Hernández Mayoral, Division of Structural Materials, CIEMAT

  11. TEM on FeCr ion irradiated Effect of Cr content Fe12Cr, 300ºC, 1 dpa Fe9Cr, 300ºC, 1 dpa Effect of dose Fe12Cr, 300ºC, 5 dpa Fe9Cr, 300ºC, 5 dpa M. Hernández Mayoral, Division of Structural Materials, CIEMAT

  12. Cr content effect on loop density • No Cr effect in density at 1 dpa, while at 5 dpa, density decreases with increasing Cr • However, density data should be “corrected” taking into account the Burgers vector: some loop families may be not visible under the imaging conditions considered • BV characterisation is in progress

  13. Cr content effect on loop size Fraction (%) Loop diameter (nm) • No big effect of Cr content is observed, especially at low dose • The effect of dose is clear with size distribution extending to larger sizes at 5 dpa

  14. Irradiation Temperature effect in Fe9Cr Size distribution Density Fraction (%) Loop diameter (nm) • Density increases when irradiation T increases (information from Burgers vector is necessary to have a good estimate of loop density ) • irrad T effect on size distribution: • No effect at 1 dpa • At 5 dpa, loop growth at 300 and 420ºC • No dose effect on size or density at 100ºC

  15. Further interpretation of results is in course In order to compare with microstructure after neutron irradiation, remember: No Cr effect at low dose (1 dpa) Fe-5, 9, 12 Cr Homogeneous distribution of loops inside the grain Indications of denuded zones close to grain boundaries in Fe12Cr

  16. Neutron irradiated materialscharacterisation by TEM M. Hernández Mayoral, Division of Structural Materials, CIEMAT

  17. Neutron irradiation conditions • Neutron irradiation in the test reactor BR2 at SCK-CEN (Belgium) • Temperature: 300°C • Fast flux ( > 1Mev) : about 1.5x10-7 dpa/s • 3 groups of specimens for 1, 3 & 5 cycles • 3 doses of 0.06, 0.6 and 1.5 dpa

  18. Effect of Cr content at 0.6 dpa, 300ºC TEM on FeCr neutron irradiated Fe5Cr Fe2Cr Fe9Cr Fe12Cr • Thereisaneffect of Cr contentondislocationloopdistribution: • Distribution of dislocationloopsappearsto be inhomogeneousfor 5, 9 and 12Cr withloopsappearingdecoratingdislocationlines and closetograinboundaries • In Fe2Cr, damageishomogeneouslydistributedinsidethegrain M. Hernández Mayoral, Division of Structural Materials, CIEMAT

  19. TEM on FeCr neutron irradiated Effect of %Cr at 0.6 dpa, 300ºC: Density • Loopsare founddecoratingdislocationlines and grainboundaries. They are found in thematrixonlyoccasionally • No cleartrendontheeffect of Cr ondensity • Note: densityispossiblyunderestimated: • Someloopfamilies are not visible • Loopsunder TEM resolution can bedistributed in thematrix M. Hernández Mayoral, Division of Structural Materials, CIEMAT

  20. TEM on FeCr neutron irradiated Effect of %Cr at 0.6 dpa, 300ºC: size • Sizedistribution: Largersize at thelowest Cr content: sizes of about 60 nm are reached, whilefor 5, 9 and 12Cr maximumsizes are around 25 nm M. Hernández Mayoral, Division of Structural Materials, CIEMAT

  21. Neutrons Ions Fe9Cr, 300ºC, 1 dpa Fe9Cr, 0.6 dpa, 300ºC Fe9Cr, 1,5 dpa, 300ºC M. Hernández Mayoral, Division of Structural Materials, CIEMAT

  22. Ions vs neutrons, quantitative data Density Average size M. Hernández Mayoral, Division of Structural Materials, CIEMAT

  23. Neutron vs ion irradiation effect • Neutron irradiated microstructure (Fe-2, 5, 9 and 12Cr, 0.6 dpa,300ºC) • Dislocation loops are inhomogeneously distributed for 5, 9 and 12 Cr with dislocation loops preferentially located close to grain boundaries and dislocation lines • Homogeneously distributed for 2%Cr: there is an effect of Cr content on the distribution of dislocation loops • Summary of results from other techniques: • PAS has detected the damage in the form of vacancy clusters revealing that, when Cr is present, the vacancy clustering is suppressed • Cr-rich a' particles have been detected by SANS and APT in the supersaturated alloys Fe9Cr and Fe12Cr. • Another family of Cr-rich nanoclusters containing also other impurity elements has been identified for each of the FeCr alloys. • Solute enrichment to dislocation lines and grain boundaries has been revealed by APT. • Ion irradiated microstructure (Fe-5, 9 and 12 Cr, 1 and 5 dpa, 300ºC) • Homogeneous distribution of loops inside the grain • Indications of denuded zones close to grain boundaries in Fe12Cr • Summary of results from other techniques • Results from APT: no ' clusters have been observed in APT ion irradiated samples, only NiSiPCr clusters • PAS: vacancy defects are detected, larger than in the case of neutron irradiation M. Hernández Mayoral, Division of Structural Materials, CIEMAT

  24. Ions vs neutrons • Need understand the microstructure produced by neutrons or by ions combination of results from complementary characterisation techniques in each case • Neutrons: reason of the different distribution of loops depending on the alloy Cr content • Differences in neutron and ion microstructure are attributed to the different flux: • No Cr rich precipitates are formed in high flux ion irradiation • Cr and other solutes redistribution due to irradiation would affect the loop structure combination of results from different characterisation techniques ------------------------------------- • Correlation with mechanical properties (talk by F. Bergner)

  25. M. Hernández Mayoral, Division of Structural Materials, CIEMAT Transmission Electron Microscopy (TEM) investigation of the microstructure evolution under neutron and ion irradiation of FeCr alloys M. Hernández-Mayoral Division of Structural Materials CIEMAT, Spain Partners within GETMAT project: L. Malerba, M. Lambrecht, SCK-CEN, Belgium C. Heintze, F. Bergner, A. Ulbricht, HZDR, Germany. C. Pareige, V. Kuksenko, B. Décamps, P. Desgardin, CNRS, France A. Idhil, C. Borca, PSI, Switzertland P. Cartemo, A. Nordlund, Sweden

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