Papers by Bertrand Radiguet
Journal of Nuclear Materials, Jul 1, 2023
Journal of Nuclear Materials, 2018
Abstract In this study, it is presented an analytical model of chemical composition correction fo... more Abstract In this study, it is presented an analytical model of chemical composition correction for nanoclusters observed by atom probe tomography, tacking into account artefacts that can bias the measured chemical compositions. After a detailed description of the model, it is exposed how it can be directly used from reconstructed dataset. Then it is applied to nanoparticles observed in an oxide dispersion strengthened steel. The model results coincide with experimental ones demonstrating its ability to quantify and correct the chemical composition bias resulting from the field evaporation. Since the analytical model does not provide explanation about the origin of the bias, field evaporation simulation are used to interpret the results. According to the simulation, composition and morphological biases result from a cross-over of ions trajectories.
Microscopy and Microanalysis, 2019
This paper describes an alternative way to assign elemental identity to atoms collected by atom p... more This paper describes an alternative way to assign elemental identity to atoms collected by atom probe tomography (APT). This method is based on Bayesian assignation of label through the expectation–maximization method (well known in data analysis). Assuming the correct shape of mass over charge peaks in mass spectra, the probability of each atom to be labeled as a given element is determined, and is used to enhance data visualization and composition mapping in APT analyses. The method is particularly efficient for small count experiments with a low signal to noise ratio, and can be used on small subsets of analyzed volumes, and is complementary to single-ion decomposition methods. Based on the selected model and experimental examples, it is shown that the method enhances our ability to observe and extract information from the raw dataset. The experimental case of the superimposition of the Si peak and N peak in a steel is presented.
Un acier austénitique inoxydable 316 écroui a été irradié aux ions Fe + de 160 keV dans le but de... more Un acier austénitique inoxydable 316 écroui a été irradié aux ions Fe + de 160 keV dans le but de reproduire le dommage engendré par les neutrons dans les réacteurs à eau pressurisée. Cet article décrit la caractérisation à l'échelle atomique, par sonde atomique tomographique assistée par laser de l'acier irradié à 1 et 5 dpa. Ces analyses ont permis d'observer la répartition des solutés après irradiation aux ions. Des fluctuations de la concentration en Si ont été observées dans l'acier irradié à 1 dpa. Dans l'acier irradié à plus haute fluence, la présence d'amas enrichis en Si a été mise en évidence.
Ultramicroscopy, 2011
Due to a high number density of grain boundaries acting as point defect sinks, ultrafine-grained ... more Due to a high number density of grain boundaries acting as point defect sinks, ultrafine-grained materials are expected to be more resistant to irradiation damage. In this context, ultrafine-grained 316 austenitic stainless steel samples have been fabricated by high pressure torsion. Their behavior under ion irradiation has been studied using atom probe tomography. Results are compared with those obtained in an ion irradiated conventional coarse-grained steel. The comparison shows that the effects of irradiation are limited and that intragranular and intergranular features are smaller in the ultrafine-grained alloy. Using cluster dynamic modeling, results are interpreted by a higher annihilation of point defects at grain boundaries in the ultrafine-grained steel.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2009
... defect (PD) clusters (nano-cavities and dislocation loops) [4] and [5] and solute (Cu, Mn, Ni... more ... defect (PD) clusters (nano-cavities and dislocation loops) [4] and [5] and solute (Cu, Mn, Ni, Si, P) clusters of nanometric size [6 ... Ion irradiations were carried out in the implantor IRMA at the Centre de Spectroscopie Nucléaire et de Spectrométrie de Masse (CSNSM Orsay) at ...
Voprosy Atomnoj Nauki i Tekhniki. Fizika Radiatsionnykh Povrezhdenij i Radiatsionnoe Materialovedenie, 2003
SSRN Electronic Journal, 2020
Quantitative study of solute segregation phenomenon is crucial in material science. In the presen... more Quantitative study of solute segregation phenomenon is crucial in material science. In the present study, the influence of thermal ageing and ion irradiation (both at 400°C) on intergranular P segregation behavior was studied by a correlative Electron Backscattering Diffraction (EBSD)/Transmission Kikuchi Diffraction (TKD)/Atom Probe Tomography (APT) methodology. The co-segregation of P, C, Si, Mn, Ni, Cr and Mo appears at Grain Boundaries (GBs). There is an increased P segregation for all the detected GB types in both thermally-aged and ion-irradiated welds. Thermodynamic and kinetic predictions confirm the Radiation Enhanced Segregation (RES) mechanism of P at GBs under ion irradiation. The ternary Fe-P-C model overestimates P segregation level in a multicomponent system.
Applied Surface Science, 2019
Intergranular segregation in a Fe-P-C model alloy after thermal ageing at 650°C has been examined... more Intergranular segregation in a Fe-P-C model alloy after thermal ageing at 650°C has been examined using Atom Probe Tomography (APT) and Auger Electron Spectroscopy (AES). The specimens were prepared using sitespecific method combining focused ion beam (FIB) and Transmission Kikuchi Diffraction (TKD). Grain boundary's five macroscopic degrees of freedom (DOFs) were determined from the TKD map supplemented by 3D APT reconstruction. The phosphorus intergranular segregation values obtained using APT and AES techniques were in excellent agreement and equal to 1.6 ± 0.7 at/nm 2 and 1.4 ± 0.5 at/nm 2 , respectively. The two techniques are complementary for a fully quantitative description.
Journal of Nuclear Materials, 2018
Ion irradiation induced Mo-Cr rich precipitates were identified using HAADF-STEM technique. Xe bu... more Ion irradiation induced Mo-Cr rich precipitates were identified using HAADF-STEM technique. Xe bubbles detected in the GH3535 alloy sample irradiated at 650 C. Dispersed barrier-hardening (DBH) model was applied to predict the irradiation hardening caused by defects. The calculated yield strength increment and the measured nanohardness increment are in excellent agreement.
RESUME : La formation d'amas diffus de solutés sous irradiation à 300°C dans les alliages bin... more RESUME : La formation d'amas diffus de solutés sous irradiation à 300°C dans les alliages binaires FeCu ayant une teneur en cuivre inférieure à 0.1% résulterait d'un mécanisme de précipitation hétérogène sur les amas de défauts ponctuels formés par irradiation. Pour pouvoir confirmer cette hypothèse, des alliages ferritiques modèles, irradiés aux neutrons sous différentes conditions de flux et de fluences, ont été analysés par Sonde Atomique Tomographique (SAT). Cette technique permet de détecter des regroupements de seulement quelques atomes de solutés. D'autre part, un modèle de dynamique d'amas, paramétré dans le cadre de cette étude, a été utilisé pour prédire la formation des amas de défauts ponctuels (DP) sous irradiation neutronique. La comparaison entre la densité d'amas de solutés obtenus expérimentalement par SAT d'une part, et la densité d'amas de DP modélisés d'autre part, permettra d'obtenir des informations sur la cinétique de format...
Philosophical Magazine, 2005
... Selected papers from the symposium held as part of the 2003 TMS Annual Meeting, San Diego, Ca... more ... Selected papers from the symposium held as part of the 2003 TMS Annual Meeting, San Diego, California, 26 March, 2003 Guest Editors: Charlotte S. Bequart, Robin E. Shäublin, Lance L. Snead and Brian D. Wirth. ... A. Barbu b , O. Zabusov c & M. Kozodaev d pages 429-441. ...
Journal of Nuclear Materials, 2010
The embrittlement of reactor pressure vessel steels under neutron irradiation is partly due to th... more The embrittlement of reactor pressure vessel steels under neutron irradiation is partly due to the formation of solute clusters. To gain more insight into their formation mechanisms, ferritic model alloys (low copper Fe-0.08 at.% Cu, Fe-0.09 Cu-1.1 Mn-0.7 Ni (at.%), and a copper free Fe-1.1 Mn-0.7 Ni (at.%)) and a French 16MND5 reactor pressure vessel steel, were irradiated in a test reactor at two fluxes of 0.15 and 9 Â 10 17 n(E> 1 MeV) m À2 s À1 and at increasing doses from 0.18 to 1.3 Â 10 24 n(E> 1 MeV) m À2. Atom probe tomography analyses revealed that nanometer-size solute clusters were formed during irradiation in all the materials, even in the copper free Fe-1.1 Mn-0.7 Ni (at.%) alloy. It should be noted that solute segregation in a low-Ni ferritic material was never reported before in absence of the highly insoluble copper impurity. The manganese and nickel segregation is suggested to result from a radiation-induced mechanism.
Journal of Materials Science, 2008
In order to get information about radiation resistance of ultrafine grained austenitic stainless ... more In order to get information about radiation resistance of ultrafine grained austenitic stainless steels, a 316 steel was deformed by high pressure torsion. The mean diameter of the grain after deformation was 40 nm. This material was annealed at 350 °C for 24 h or irradiated with 160 keV iron ions at 350 °C. Changes in the microstructure during annealing or irradiation were characterised by transmission electron microscopy (grain size) and laser assisted tomographic atom probe (solute distribution). Results indicate that this annealing has no influence on the grain size whereas the grain diameter increases under irradiation. Concerning the solute distribution, atom probe investigations show evidence of radiation-induced segregation at grain boundaries. Indeed, after irradiation, grain boundaries are enriched in nickel and silicon and depleted in chromium. On the contrary, no intragranular extended defects or precipitation are observed after irradiation.
Journal of Nuclear Materials, 2008
We report the calibration of a rate theory numerical code capable to reproduce the agglomeration ... more We report the calibration of a rate theory numerical code capable to reproduce the agglomeration of point-defects produced in a-iron by irradiation under cascade damage conditions. The input parameters are obtained by performing transmission electron microscopy (TEM) experiments in a-iron. It was irradiated at temperatures between 200 and 400°C with high flux krypton ion under resolvable point-defect cluster conditions. The TEM analyse of the sample irradiated at the highest temperature reveals the presence of two dislocation loop populations: large ones are decorated with small ones, both vacancy and interstitial in type. The vacancy loops are proposal to be located in the compressive side of the large interstitial loops.
Materials Today Physics
Radiation-induced embrittlement of nuclear steels is one of the main limiting factors for safe lo... more Radiation-induced embrittlement of nuclear steels is one of the main limiting factors for safe long-term operation of nuclear power plants. In support of accurate and safe reactor pressure vessel (RPV) lifetime assessments, we developed a physics-based model that predicts RPV steel hardening and subsequent embrittlement as a consequence of the formation of nano-sized clusters of minor alloying elements. This model is shown to provide reliable assessments of embrittlement for a very wide range of materials, with higher accuracy than industrial correlations. The core of our model is a multiscale modelling tool that predicts the kinetics of solute clustering, given the steel chemical composition and its irradiation conditions. It is based on the observation that the formation of solute clusters ensues from atomic transport driven by radiation-induced mechanisms, differently from classical nucleation-and-growth theories. We then show that the predicted information about solute clustering can be translated into a reliable estimate for radiation-induced embrittlement, via standard hardening laws based on the dispersed barrier model. We demonstrate the validity of our approach by applying it to hundreds of nuclear reactors vessels from all over the world.
Metals, 2022
The existing knowledge about the effect of neutron irradiation on the mechanical properties of re... more The existing knowledge about the effect of neutron irradiation on the mechanical properties of reactor pressure vessel steels under reactor service conditions relies to a large extent on accelerated irradiations realized by exposing steel samples to a higher neutron flux. A deep understanding of flux effects is, therefore, vital for gaining service-relevant insight into the mechanical property degradation. The existing studies on flux effects often suffer from incomplete descriptions of the irradiation-induced microstructure. Our study aims to give a detailed picture of irradiation-induced nanofeatures by applying complementary methods using atom probe tomography, positron annihilation, small-angle neutron scattering and transmission electron microscopy. The characteristics of the irradiation-induced nanofeatures and the dominant factors responsible for the observed increase of Vickers hardness are identified. Microstructural changes due to high flux conditions are smaller nm-sized ...
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Papers by Bertrand Radiguet