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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

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; 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