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International audience; Les aciers ODS (Oxide Dispersion Strengthened) contiennent une fine dispersion d'oxydes Y-Ti-O au sein de leur matrice metallique. Ces nano-oxydes visent a ameliorer les proprietes en fluage et la resistance aux irradiations de ces aciers. Les aciers ODS sont elabores par metallurgie des poudres. C'est-a-dire qu'une poudre d'acier est broyee avec des poudres de renforts (Y2O3 et TiH2) afin d'incorporer les atomes d'yttrium et de titane dans la matrice. A l'issue de cette etape, la poudre obtenue est de morphologie non spherique et ne contient aucun oxyde forme. Ce sont les etapes ulterieures de consolidation de la poudre, par extrusion a chaud ou par consolidation isostatique a chaud, qui permettront de faire germer les oxydes au sein de la matrice. Ces procedes conventionnels de mise en forme permettent d'elaborer des materiaux aux geometries simples. Les procedes de fabrication additive se sont considerablement developpes ces dernieres annees. Ils sont passes de procedes de prototypage rapide a des procedes technologiques pour la realisation de composants a forte valeur ajoutee. Ces procedes permettent une grande liberte quant a la geometrie finale des composants. Les aciers ODS etant d'abord obtenus sous forme de poudre, il est interessant d'envisager leur mise en forme par ces procedes innovants. Le procede de fusion laser sur lit de poudre ou procede SLM est un procede d'elaboration couche par couche par fusion de poudre metallique a l'aide d'un laser. A chaque couche, de la poudre est etalee sur une fine epaisseur puis le laser vient fusionner les zones d'interet. La poudre devant etre etalee, il est necessaire que celle-ci presente une excellente coulabilite. Ce n'est pas forcement le cas des poudres broyees d'aciers ODS puisqu'elles sont de morphologie non spherique.Les poudres d'aciers ODS peuvent etre traitees par torche plasma avant d'etre utilisees en fabrication additive. Ce traitement rapide a haute temperature permet d'obtenir des poudres spheriques. Les caracteristiques des poudres broyees d'acier ODS, traitees ou non par torche plasma, sont etudiees. La morphologie, la granulometrie ainsi que la coulabilite de chaque poudre sont comparees. L'influence de toutes ces caracteristiques sur les proprietes finales des materiaux elabores par procede SLM est ensuite etudiee. Il a ete constate que la granulometrie des poudres a une influence forte sur les proprietes finales des materiaux. Plus la poudre est fine et plus la gamme de parametres operatoires permettant d'obtenir des materiaux denses par procede SLM est large. Les poudres spheriques permettent d'obtenir des couches de poudre plus compactes que celles formees a partir de poudre non spherique. La spheroidisation des poudres d'acier ODS est un reel apport pour l'elaboration de ces composants par fabrication additive.

International audience; This study investigates the feasibility to produce complex ODS Fe-14Cr steel parts by an additive manufacturing process such as selective laser melting (SLM). Milled powder, which is composed of non-spherical shape particules, is used as raw material. The main aim of this work is to assess the effect of each single processing parameter on the properties of SLM builds. Optimization of the process parameters allows to get ODS steel parts, which present high density up to 98percent and a fine dispersion of nanosized Y-Ti rich oxide particles. It is shown that an increase in laser power coupled with a decrease of hatch distance as well as the scan speed induce a coarsening of the microstructure. A precise control of the processing parameters allows to tune the microstructure in accordance to the target use of the built ODS steel parts. Since their microstructure is different from the one observed in ODS steel elaborated by conventional routes, new high temperature applications for ODS steels could be explored such as complex heat exchangers built in a single-step.

International audience; Additive manufacturing processes are promising technologies, currently considered as new opportunities to optimize metallic components production routes, especially in aerospace, automotive, medical and energy industries. To assess the potentialities of additive manufacturing in nuclear industry, ODS (Oxide Dispersion Strengthened) Fe-14Cr steels are produced by selective laser melting (SLM). ODS steels are studied due to their improved resistance under neutron irradiation thanks to a fine dispersion of nanosized Y-Ti-O precipitates. Such materials are produced by a first step of mechanical alloying. The resulting powder has a non-spherical shape and is coarser than powders typically used in SLM equipment. The analyzes such as composition, density, particles size distribution, flowability and morphology are performed on this powder. The milled powder is then used to produce ODS steel parts as raw material or after some modifications such as sieving. The objective of this work is to study the impact of the powder characteristics on the final material properties. As expected, powder characteristics strongly influence the final density of solidified parts. The choice of the thickness layer is also an important parameter that has to be related with the particle size distribution of the powder.

International audience; Ces dernières années, les techniques de fabrication additive permettant de fabriquer couche par couche des pièces de géométries complexes sont le centre d’un intérêt croissant. Le procédé de fusion laser de poudre projetée (Direct Metal Deposition, DMD) permet également d’envisager la fabrication de matériaux à gradient de composition. Dans ce procédé, la poudre est directement projetée à travers une buse dans le bain de fusion généré par le passage d’un faisceau laser. Ainsi, il est possible de contrôler directement la composition du matériau final par le débit de poudre, en utilisant différents bacs d’alimentation. Ces matériaux à gradients de composition sont étudiés pour des applications industrielles comme matériaux fonctionnels ([1], [2]) ou comme solutions à des problèmes de soudage ([3], [4]). Cette étude se concentre sur un gradient depuis un acier austénitique 316L vers un acier martensitique 9Cr-1Mo. Ces aciers sont fréquemment utilisés dans les applications nucléaires, mais leurs grandes différences de composition chimique rendent leur soudage difficile.Dans cette étude, trois procédés de fabrication sont étudiés : Compression Isostatique à Chaud, frittage flash SPS et fabrication additive par DMD. Les microstructures ainsi obtenues sont étudiées par Microscopie Electronique à Balayage (MEB) et Electron BackScatter Diffraction (EBSD), puis corrélées à des calculs thermodynamiques et de diffusion. Les relations entre propriétés mécaniques, microstructures et paramètres opératoires sont étudiées.

International audience; Dans le contexte actuel d'optimisation du parc actuel et futur et de l'allongement de la duree de vie des centrales et des installations du cycle, la problematique de duree de vie des materiaux est cruciale. Les problematiques de vieillissement et de reactivite (corrosion) constituent un defi majeur dans l'industrie nucleaire. Pour relever l'ensemble de ces defis, les technologies innovantes dans le domaine des procedes de traitements de surfaces avec ou sans apport de matiere sont des solutions prometteuses d'autant plus que ces dernieres ont connu un developpement significatif ces dernieres annees.Parmi les technologies de traitement de surface etudiees au Service d'Etudes Analytiques et de Reactivite des Surfaces (SEARS) de la DEN (Division de l'Energie Nucleaire), les techniques par laser sont historiquement presentes grace aux competences du LISL (Laboratoire d'Ingenierie des Surfaces et Lasers). Une premiere appartient a la famille des traitements sans apport de matiere. Elle consiste a venir frapper une surface avec un laser dont les proprietes sont judicieusement choisies pour que la matiere presente soit fondue voire ejectee. En pilotant les caracteristiques du faisceau laser incident les proprietes de surface peuvent etre modifiees. Il est par exemple possible de former une couche barriere d'oxydes, d'homogeneiser des phases et d'augmenter la teneur en certains elements chimiques voire de modifier la structure cristallographique ce qui peut conduire a une augmentation de la durete. Les applications de ce procede sont le renforcement de la resistance a la corrosion par piquration d'aciers 304L ou la limitation du relachement de nickel en milieu primaire au niveau des generateurs de vapeur. Enfin, l'ejection de matiere provenant de la surface traitee peut etre maximisee pour utiliser ce traitement comme une technique d'ablation surfacique pour le demantelement ou la maintenance d'installations, son point fort etant la possibilite de decontaminer des composants a distance.Les autres traitements de surface concernent des methodes avec apport de matiere. Parmi les technologies etudiees, certaines passent par un etat gazeux de la matiere. Suivant si la phase gazeuse se condense ou se decompose a la surface du composant a revetir, on parlera de PVD (condensation) ou de CVD (decomposition avec reaction chimique). Ces techniques sous vide sont majoritairement employees pour deposer des revetements protecteurs afin d'augmenter les performances et les durees de vie de composants en milieux extremes (haute temperature, irradiation, oxydation, corrosion ou encore usure abrasive). On peut citer les developpements actuels avec Areva pour les EATFs (Enhanced Accident Tolerant Fuels) concernant les gaines de combustible nucleaire qui, avec un revetement protecteur, resisteraient bien mieux a des hypothetiques conditions accidentelles de perte de refrigerant primaire.

International audience; Low-alloy ferritic steel (16MND5) is used for pressure vessels in French nuclear reactors, where radiationinduced defects are continuously nucleated during their operational lifetime. More specifically, such defects have a major influence on the collective behavior of dislocations, leading to a significant hardening and embrittlement. A multiscale modeling approach based on a combination of molecular dynamics and dislocation dynamics simulations is therefore adopted. Interactions of edge dislocations with radiation-induced defects have been widely studied compared to those of screw dislocations. The later are nevertheless of great interest as their specific mobility has a significant impact on the mechanical properties of steels at low and moderate temperatures. Furthermore, prior molecular dynamics(MD) studies[1, 2] have shown that their interactions with irradiation loopslead to significant hardening. In this study, a systematic investigation is made of the interactions between screw dislocations with [100] and [111] loops using a three-dimensional nodal dislocation dynamics (DD) code NUMODIS. The same configurations that were previously simulated with MD are successfully reproduced. This allows for a direct comparison between atomic scale and DD simulations to validate our multiscale strategy. Ultimately, the modeling of the collective behavior of dislocations properties controlling irradiation strengthening will be undertaken in order to identify and incorporate the relevant parameters in a crystal plasticity simulation.

International audience

International audience; Oxide Dispersion Strengthened (ODS) ferritic steels typically contain a fine dispersion of nanosized Y-Ti-O precipitates, leading to an improvement of creep properties and neutron swelling resistance. These alloys are usually manufactured by different successive steps: mechanical alloying, outgassing, hot extrusion and cold working. Mechanical alloying aims at the dissolution of Y and Ti atoms into the ferritic matrix. This process leads to the precipitation and growth of fine Y-Ti-O oxide dispersoids during the heat treatments and the consolidation by hot isostatic pressing and/or by hot extrusion. Considering the limitations regarding the final shapes complexity of components obtained by this traditional fabrication route, the evaluation and development of alternative production methods are currently studied in order to increase the widespread use of ODS alloys. In the frame of assessing the potentialities of additive manufacturing to manufacture ODS complex parts, a Fe14Cr1W + 0.3percent Y2O3 + 0.3percent TiH2 milled powder is consolidated by Selective Laser Melting (SLM). The influence of processing parameters (scanning speed, scanning strategy, laser power, etc…) on the final microstructures as well as the final densities are studied. For this purpose, several microstructural techniques (scanning electron microscopy, electron backscattered diffraction & transmission electron microscopy) are coupled in order to analyze the cross-sections. First results are quite promising since density of more than 98percent could be achieved with a non-optimized powder. As expected, processing parameters strongly influence the microstructural evolution, especially the grains size and the precipitates’ density. The influence of powder properties, such as particles size distribution and flowability, on the final properties are also studied and presented in details. The objective of this work is to demonstrate how process parameters tailor the microstructure of such alloys and so final mechanical properties.

International audience; Additive manufacturing processes are promising technologies, currently considered as new opportunities to optimize metallic components production routes, especially in aerospace, automotive, medical and energy industries. The development of the application fields of these technologies involves an increase in the number of possible printed materials. In order to become a robust and reliable way of production of metallic functional components, mastering these technologies must still address challenges. In this framework, the study of the defects impact on final properties of designed components is essential.To assess the potentialities of additive manufacturing in nuclear industry, ODS Fe-14Cr steels are produced by selective laser melting (SLM). ODS steels are studied due to their improved resistance under neutron irradiation thanks to a fine dispersion of nanosized Y-Ti-O precipitates. Such materials are produced by a first step mechanical alloying. The resulting powder is characterized by a non-spherical shape and are coarser than powders typically used in SLM equipment. The analyzes such as composition, density, particles size distribution, flowability and morphology are performed on this powder. The milled powder is then used to produce ODS steel parts as raw material or after some modifications such as sieving or annealing.The objective of this work is to study the impact of the powder characteristics on the final material properties. As expected, powder characteristics strongly influence the final density of solidified parts. The choice of the thickness layer is also an important parameter that has to be related with the particle size distribution of the powder. The optimization of processing parameters (scanning speed, scanning strategy, laser power, etc…) and powder characteristics lead to a significant improvement of final material properties. In this context, last results regarding ODS steels additive manufacturing study will be presented and new insights for industrial fabrication will be given.

International audience

International audience; Among the numerous laser applications, laser surface melting by using a pulsed-laser is an innovative technology in the field of surface treatments. This technique presents many advantages. It only modifies the surface properties by keeping the mechanical properties of the bulk. It requires neither addition of other compounds nor contact, so it is quite economical and it does not pollute the material. It allows the treatment of complex shapes into closed spaces with difficult access. The laser can work in autonomy that present an interest in the fields of nuclear decontamination.This treatment consists in focusing a nanopulsed laser beam on the surface of the material, leading to the rather immediate melting of the surface through a micron depth, immediately followed by an ultra-fast solidification occurring with cooling rate up to 1010 K/s.By using different techniques of analysis, we showed that the combination of these processes leads to various modifications of surface properties. By combining with dexterity the different laser parameters, it is possible to functionalize the surface or to improve the native properties.Glow discharge optical emission spectrometry (GDOES), XPS and TEM were used to establish the segregation of chemical elements and the growth of a new oxide layer with new properties.XRD with grazing incidence was employed to identify the change of crystallographic structure, SEM was performed to promote the diminution of the surface defects and the microstructure.Applications in fields of nuclear will be presented, especially in terms of pitting corrosion of stainless steel used in secondary circuit, and protection against the nickel release of heat exchanger tubes in the primary circuit coolant.

National audience; Des aciers ODS Fe-14Cr ont ete elabores par fusion laser selective sur lit de poudres. L'influence des parametres operatoires et celle de la granulometrie de la poudre sur la densite et la microstructure des materiaux ont ete etudiees. Les premieres experiences realisees montrent que les materiaux sont plus denses a puissance laser elevee (> 150 W) et a vitesse de balayage du laser faible (< 300 mm/s). Les premieres observations microstructurales ont egalement revele la presence d'une repartition fine (< 200 nm) et homogene de nano-precipites, riches en titane et en yttrium, au sein des materiaux consolides.

International audience; Among the numerous laser applications, laser surface melting by using a pulsed-laser is an innovative technology in the field of surface treatments. This technique presents many advantages. It only modifies the surface properties by keeping the mechanical properties of the bulk. It requires neither addition of other compounds nor contact, so it is quite economical and it does not pollute the material. It allows the treatment of complex shapes into closed spaces with difficult access. The laser can work in autonomy that present an interest in the fields of nuclear decontamination.This treatment consists in focusing a nanopulsed laser beam on the surface of the material, leading to the rather immediate melting of the surface through a micron depth, immediately followed by an ultra-fast solidification occurring with cooling rate up to 1010 K/s.By using different techniques of analysis, we showed that the combination of these processes leads to various modifications of surface properties. Glow discharge optical emission spectrometry (GDOES) and transmission electronic microscopy (TEM) were used to establish the segregation of chemical elements and the growth of a new oxide layer with new properties.X-Ray diffraction (XRD) with grazing incidence was employed to identify the change of crystallographic structure, scanning electron microscopy (SEM) was performed to promote the diminution of the surface defects and the roughness was also characterized.Applications in fields of nuclear, corrosion, and decontamination will be presented. Those results showed that the new surface properties strongly depend of the laser parameters.

International audience; In the framework of the fabrication of 316L stainless steel (SS) components by laser additive manufacturing (LAM), the influence of process parameters on microstructure and mechanical properties was studied. Test-specimens, such as cubes and cylindrical samples, were processed by Selective Laser Melting using SLM Solutions GmbH 280HL device. The raw 316L SS powder provided by SLM Solutions GmbH was firstly characterized. Physico-chemical properties such as composition, density, particles size distribution, powder flowability and morphology were investigated and compared with ten commercial 316L SS powders. The impact of process parameters on the microstructure of the manufactured specimens was studied, taking the physico-chemical properties of the powder into account. For this purpose, several observation techniques (SEM, EBSD measurements and TEM) were coupled in order to characterize the microstructure of the specimens' cross-sections. The results showed that the microstructure of the specimens is composed by columnar grains, oriented in the Z-direction and divided into fine intragranular cells. Nano-sized oxide precipitates were observed inside the austenitic matrix. For each specimen, texture, grain size and precipitates were examined with the aim of correlating the process parameters to the microstructure. The impact of process parameters on the mechanical behaviour of the manufactured specimens was finally studied. Mechanical tests were performed on machined samples yield strength, tensile strength, elongation, absorbed energy and hardness were measured and then compared. In this framework, last results regarding the influence of process parameters of AM on microstructure and mechanical properties of 316L SS will be presented and new insight for an optimization of these parameters will be given.

ISBN : 978-1-5108-5000-2; International audience; In this article, we present the ongoing study concerning the selection of cobalt free hardfacing materials for wear resistance in the French Sodium Fast Neutron Reactor ASTRID, currently under development. In the reactor, some parts can be submitted to sliding contact between each other. On these parts, the contact areas usually need a hardfacing coating. The standard hardfacing alloy is a cobalt-base alloy (as, for example Stellite6). Unfortunately, in the primary coolant circuit and on wear conditions, cobalt can be released. Under neutron flux, the 59Co, stable, can be transmuted into $^{60}$Co by neutrons irradiation and, therefore, can contaminate the primary circuit and will be an issue for deconstruction. Therefore, it is desired to replace this cobalt based hardfacing alloy by a cobalt-free one. First, we present the selection of some promising materials and processes selected from the bibliography and previous achieved works. Two processes are used for manufacturing the clads Plasma Transferred Arc and the Laser Cladding. From the bibliography, different nickel base alloys have been selected. In the presentation, we consider our investigations made on Colmonoy 5. The cobalt base alloy Stellite 6 is evaluated as the reference. The microstructure of the Colmonoy 5 is compared for the two processes. Then, different properties of the clad are evaluated by mechanical, aging, and wear tests. In the project, two tribometers based on planar and linear sliding at high temperature have been set up one under inert gas protection and one under liquid sodium at operating temperature. After the presentation of the tribometers, wear tests are presented and the wear behavior of the Colmonoy 5 deposits is discussed. Finally, conclusion is given on the quality of the material to be a substitute of cobalt base material.

International audience

International audience; In order to improve the safety of nuclear power plant, loss-of-coolant accident experiments areimplemented in research reactor. In this framework, we develop an optical pyrometry device to measuresurface temperature (700-1200°C) of Zircaloy cladding without contact. The whole set-up of thesimplified device (under air, without radiation) and the measurement procedure including data treatmentbased on bichromatic pyrometry are presented, as well as results for various temperature levels.Temperature retrieval based on the hypothesis of emissivity ratio equal to a constant, is scanned over alarge wavelength range. A constant surface temperature is obtained on the spectral range ofmeasurement, confirming the relevancy of emissivity hypothesis. Differences between this non-contacttemperature measurement and a complementary thermocouple temperature measurement are alsodiscussed.

International audience; The Fukushima-Daiichi nuclear disaster showed that the need for safety must always prevail. This paper discusses the development of remote monitoring technologies to improve Nuclear Power Plants (NPPs) safety, in operation (Pressurized Water Reactors), under construction (the EPR reactors, i.e. the GEN 3 PWR), or for any other next generations of reactors. At Fukushima, the total loss of electrical power supplies has quickly led most of the instrumentation inoperative and the operator (TEPCO) with no way to monitor the status and the evolution of the accident. To overcome these important drawbacks, advantage can be taken from the considerable potential of distributed sensing technologies based on both "Optical Fiber Sensors" (Raman, Brillouin, and Rayleigh Reflectometries) and long-length "Self Powered Neutron Detectors" (SPNDs). The goal consists in inquiring about the status of the third barrier of confinement and to define possible mitigation strategies in case of severe accident, namely: i) reactor pressure vessel breakthrough and corium relocation outside the vessel, ii) concrete basemat erosion and iii) corium cooling. Such monitoring should consist in "sensing cables" embedded in concrete basemat below the reactor vessel and interrogated from a rear base where operators can work safely. In this context, DISCOMS, which stands for "DIstributed Sensing for COrium Monitoring and Safety", is a five-year project, managed by the French National Research Agency (ANR), dealing with the NPP safety improvement, from normal situation to severe accidents. Monitoring phases include reactor vessel breaching, corium flow, along with post-accidental period (corium cooling ex-vessel). Thus, optical fibers selected for their resistance to ionizing radiations and long length SPNDs, both judiciously deployed within the reactor concrete basemat, and the structures around it, will provide a useful real-time or on-demand monitoring, in normal operation, and more important in accidental and post-accidental situations.

International audience; The Fukushima-Daiichi nuclear disaster showed that the need for safety must always prevail. This paper discusses the development of remote monitoring technologies to improve Nuclear Power Plants (NPPs) safety, in operation (Pressurized Water Reactors), under construction (the EPR reactors, i.e. the GEN 3 PWR), or for any other next generations of reactors. At Fukushima, the total loss of electrical power supplies has quickly led most of the instrumentation inoperative and the operator (TEPCO) with no way to monitor the status and the evolution of the accident. To overcome these important drawbacks, advantage can be taken from the considerable potential of distributed sensing technologies based on both "Optical Fiber Sensors" (Raman, Brillouin, and Rayleigh Reflectometries) and long-length "Self Powered Neutron Detectors" (SPNDs). The goal consists in inquiring about the status of the third barrier of confinement and to define possible mitigation strategies in case of severe accident, namely: i) reactor pressure vessel breakthrough and corium relocation outside the vessel, ii) concrete basemat erosion and iii) corium cooling. Such monitoring should consist in "sensing cables" embedded in concrete basemat below the reactor vessel and interrogated from a rear base where operators can work safely. In this context, DISCOMS, which stands for "DIstributed Sensing for COrium Monitoring and Safety", is a five-year project, managed by the French National Research Agency (ANR), dealing with the NPP safety improvement, from normal situation to severe accidents. Monitoring phases include reactor vessel breaching, corium flow, along with post-accidental period (corium cooling ex-vessel). Thus, optical fibers selected for their resistance to ionizing radiations and long length SPNDs, both judiciously deployed within the reactor concrete basemat, and the structures around it, will provide a useful real-time or on-demand monitoring, in normal operation, and more important in accidental and post-accidental situations.