Littérature scientifique sur le sujet « Aciers renforcés par dispers »
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Articles de revues sur le sujet "Aciers renforcés par dispers"
Pantelis, D., P. Manolatos, G. Pantazopoulos et P. Ponthiaux. « Comportement en usure-frottement des aciers à outils renforcés en surface par traitement laser avec injection d’une poudre de SiC ». Revue de Métallurgie 91, no 5 (mai 1994) : 745–56. http://dx.doi.org/10.1051/metal/199491050745.
Texte intégralNYS, Y. « Préface ». INRAE Productions Animales 23, no 2 (10 avril 2011) : 107–10. http://dx.doi.org/10.20870/productions-animales.2010.23.2.3292.
Texte intégralThèses sur le sujet "Aciers renforcés par dispers"
Autones, Lucas. « Élaboration d’aciers ODS (Oxide Dispersion Strengthened) par fabrication additive laser et cold spray : compréhension des relations procédés - microstructures ». Electronic Thesis or Diss., Université de Lille (2022-....), 2022. http://www.theses.fr/2022ULILR004.
Texte intégralODS (Oxide Dispersion Strengthened) steels are materials that exhibit very good resistance to creep and swelling under irradiation. These properties make them good candidates for cladding materials in Generation IV reactors, or for structural materials in thermonuclear fusion reactors. The dispersion of the nano-oxides, which reinforce the material, is obtained by powder metallurgy. Mechanical-alloying of an atomized steel powder with an oxide powder (Y2O3) results in the oxide dissolution in the matrix. During hot consolidation (hot isostatic pression or hot extrusion), the precipitation of the nano-oxides takes place. Designs of component with these materials and their final geometry could be improved using additive manufacturing.Since the 2010s, recent developments in additive manufacturing technologies could enable to reduce lead times and costs, while increasing the geometric, hierarchical and functional complexity of parts. They pave the way to new freedom of design compared to conventional subtractive manufacturing processes.The objective of this thesis work was to assess the potentials of different additive manufacturing techniques (SLM, DMD, and Cold Spray) for ODS steels.Thus, three types of ODS powder (mechanically-alloyed, composite and STARS) were obtained to determine the most interesting powder-process combinations. The materials produced from these different combinations have been characterized at several scales. The amount of macroscopic defects (porosities, cracks) was analyzed in order to optimize the manufacturing parameters. Their granular microstructure was observed before and after annealing at 1100 °C by optical and electron microscopy (SEM, EBSD). The nano-precipitation was analyzed by SEM, TEM and by small angle X-rays scattering. An image analysis method combining high definition electron microscopy images and a machine learning software was implemented. Finally, the high temperature tensile properties of these different materials were evaluated and are in good agreement with their microstructural characteristics. The comparison of the whole characterization results enabled to select the relevant manufacturing paths.The results obtained indicate that laser additive manufacturing processes (SLM, DMD) lead to ODS steels with low performance, regardless the type of powder used. The yttrium content can greatly decrease after consolidation. It also forms fragile Y-rich coarse phases, and the density of the nano-precipitates population appears very low. These microstructural characteristics induce tensile properties equivalent to those of an unreinforced steel. Nevertheless, the composite powder elaboration method implemented in this work makes it very easy to adapt the nature and content of the reinforcements added to the base powder. Using TiC nano-particles, very fine microstructures composed of equiaxed grains were obtained. These unusual microstructures in laser additive manufacturing offer interesting prospects.ODS steels obtained by cold spray from a mechanically-alloyed powder have characteristics similar to conventional ODS steels. After annealing, these materials have a microstructure similar to the ODS steels obtained by HIP. However, the coarse grains take up a much larger fraction of the microstructure and attest to a more advanced recrystallization. The lower hardness and elastic limit of this material compared to its HIP equivalent confirm this result, which is very encouraging if further shaping should be aimed. The very high density of Y-Ti-O nano-oxides in the Cold Sprayed ODS steel enables to achieve a mechanical resistance at 700 °C which is 50 MPa higher than the HIPed ODS. However, this material exhibits a loss of ductility which will have to be resolved. The analyzes carried out enabled to suggest two mechanisms to explain this damage, which would be caused by the presence of microcracks and porosities in the part
Steckmeyer, Antonin. « Caractérisation et modélisation du comportement mécanique à haute température des aciers ferritiques renforcés par dispersion d'oxydes ». Phd thesis, Ecole Nationale Supérieure des Mines de Paris, 2012. http://pastel.archives-ouvertes.fr/pastel-00819136.
Texte intégralSalmon, legagneur Hubert. « Caractérisation de l’endommagement à haute température d’aciers ferritiques renforcés par dispersion de nano-oxydes (ODS) ». Thesis, Paris Sciences et Lettres (ComUE), 2017. http://www.theses.fr/2017PSLEM034/document.
Texte intégralThe development of the fourth generation of nuclear power plants relies on the improvement of cladding materials, in order to achieve resistance to high temperature, stress and irradiation dose levels. Strengthening of ferritic steels through nano-oxide dispersion allows obtaining good mechanical strength at high temperature and good resistance to irradiation induced swelling. Nonetheless, studies available from open literature evidenced an unusual creep behavior of these materials: high anisotropy in time to rupture and flow behavior, low ductility and quasi-inexistent tertiary creep stage. These phenomena, and their still unclear origin are addressed in this study.Three 14Cr ODS steels rods have been studied. Their mechanical behavior is similar to those of other ODS steels from open literature. During creep tests, the specimens fractured by through crack nucleation and propagation from the lateral surfaces, followed by ductile tearing once the critical stress intensity factor was reached at the crack tip. Tensile and creep properties did not depend on the chemical environment of specimens. Crack propagation tests performed at 650°C showed a low value of the stress intensity factor necessary to start crack propagation. The cracks followed an intergranular path through the smaller-grained regions, which partly explains the anisotropy of high temperature strength.Notched specimens have been used to study the impact of the main loading parameters (deformation rate, temperature, stress triaxiality) on macroscopic crack initiation and stable propagation, from the central part of the specimens.These tests allowed revealing cavities created during high temperature loading, but unexposed to the external environment. These cavities showed a high chemical reactivity of the free surfaces in this material. The performed tests also evidenced different types of grain boundaries, which presented different damage development behaviors, probably due to differences in local chemistry. The nature of these grains boundaries and their origin are still to be explained
Rouffié, Anne-Laure. « Compréhension et modélisation de la rupture fragile des aciers renforcés par nano-précipitation : effets de texture, de vieillissement et de composition ». Phd thesis, Ecole Nationale Supérieure des Mines de Paris, 2014. http://pastel.archives-ouvertes.fr/pastel-01069061.
Texte intégralKarch, Abdellatif. « Étude des évolutions microstructurales lors de la transformation à chaud d’aciers ferritiques renforcés par dispersion d’oxydes ». Thesis, Paris, ENMP, 2014. http://www.theses.fr/2014ENMP0075/document.
Texte intégralThe production of ODS steels involves a powder consolidation step usually using the hot extrusion (HE) process. The anisotropic properties of extruded materials, especially in the ODS ferritic grades (>wt%12Cr), need a better understanding of the metallurgical phenomena which may occur during HE and lead to the observed microstructure. The hot working behavior of these materials is of particular interest. The methodology of this work includes the microstructure analysis after interrupted hot extrusion, hot torsion and hot compression (1000-1200°C) tests of ferritic steels with 14%Cr and different amounts in Ti and Y2O3.The microstructure evolution during hot extrusion process is associated with continuous dynamic recrystallization (CDRX). It leads to the creation of new grains by the formation of low angle boundaries, and then the increase of their misorientation under plastic deformation. The investigations highlight also the role of precipitation on the kinetics of this mechanism; it remains incomplete in the presence of fine and dense nanoprecipitates. After hot deformation in torsion and compression, it is noticed that both precipitates and temperature deformation have a significant impact on the deformation mechanisms and microstructure evolution. Indeed, the CDRX is dominant when temperature and amount of reinforcement are limited. However, when they are increased, limited microstructure evolution is observed. In this case, the results are interpreted through a mechanism of strain accommodation at grain boundaries, with low dislocation activity in the bulk of the grains
Spartacus, Gabriel. « Evolution des nano-oxydes et de la microstructure au cours du procédé de fabrication d'aciers renforcés par dispersion d'oxydes ». Thesis, Université Grenoble Alpes, 2020. http://www.theses.fr/2020GRALI085.
Texte intégralOxide Dispersion Strengthened (ODS) steels with a Fe-Cr matrix are of great interest in the development of generation IV fission nuclear power plants as a fuel cladding material. These materials, elaborated by powder metallurgy, include a high density of Y-Ti-O oxide precipitates of a few nm, providing the main contribution to the ODS steels strength. During the fabrication process, powders of Fe-Cr steel, Y2O3 and TiH2 are milled together to obtain a super-saturated solution of Y, Ti and O, otherwise insoluble in Fe. The obtained powder is subsequently processed by Hot Extrusion or Hot Isostatic Pressing around 1100℃. This induces the precipitation of Y-Ti-O and leads to a fully dense steel with finely dispersed nano-oxides in high density, extremely stable even at very high temperature. Moreover, the complex microstructure induced by the milling stage, including high density of dislocations and very small grain size, also evolve during the heating, in an intricate ways with the evolution of the nano-oxides that act as strong pinning points for both grain boundaries and dislocations. This features leads to abnormal grain growth (significant growth of some grains, while others remain stable) and therefore a bimodal grain size after consolidation.The aim of this thesis is to characterize both kinetics and chemical evolution of the nano-oxides during the fabrication process of these steels, as well as the grain microstructure evolution, which are still misunderstood. Such experimental characterization would be invaluable to further control the fabrication process and improve available model of the ODS precipitation kinetics. For this purpose, cold pressed specimens from as-milled powder were prepared (in order to achieve dense specimens without precipitation) and observed by means of various in-situ or ex-situ techniques. In particular, in-situ Small Angle X-ray Scattering measurements were performed during the heating until 1100℃ to measure the precipitation kinetics of several ODS grades. The chemistry and structure of nano-oxides were assessed thanks to anomalous SAXS at Y (performed in-situ) and Ti (ex-situ) edges, ex-situ small angle neutron scattering and atom probe tomography. Then, the grain microstructure was monitored by in-situ X-ray diffraction.These characterizations allow to describe the whole kinetics of purely ferritic ODS, ferritic / martensitic ODS and ODS strengthened with variation of the strengthening powders. In particular, this study highlights a non-homogeneous as-milled stage with clusters containing Y, O and Ti in lesser extent. These clusters evolve in chemistry and structure until reaching a stable structure and stoichiometry, revealed to be Y2Ti2O7 pyrochlore and Y2TiO5 orthorhombic depending on the ODS steel grade. Moreover, a kinetic modification induced by the in temperature phase transformation of the matrix in the ferritic / martensitic ODS (increasing the growth and coarsening rate) was observed. Correlation between nano-oxide and the grain microstructure evolutions were performed and help in the comprehension of the abnormal grain growth temperature and final grain morphology, from one ODS grade to another. Finally, comparisons of the precipitation simulations with experimental data allow to get more insights on the nano-oxides properties
Emelianova, Olga. « Modeling gas-driven microstructural evolution in ODS-EUROFER steel by high dose helium and hydrogen ion implantation ». Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPASP056.
Texte intégralOxide dispersion strengthened (ODS) ferritic-martensitic steels are advanced high-performance structural materials for next generation nuclear and fusion facilities. An important issue for operation performance of these steels is their resistance to detrimental effects of transmutation gases, helium and hydrogen, with a particular attention to the effects from dense population of nano-size oxide particles. The objective of the thesis is a systematic investigation of fundamental trends in gas-driven microstructure development in ferritic-martensitic ODS steels in reply to variations in the accumulated gas content, gas accumulation and damage rates, and temperature, with particular attention to the role of oxide particles. The applied experimental approach involved saturation of steel samples with various amounts of helium and hydrogen atoms using ion implantation at the JANNuS-Orsay facility in well-controlled conditions. The reference material used was ODS-EUROFER steel. The microstructural changes accompanying gas accumulation were revealed using transmission electron microscopy (TEM). For the better understanding of the mechanisms of helium interaction with oxide particles, the experiments were backed up with ion implantation into a model Y₂O₃/FeCr bilayer system and with relevant analytical and numerical modeling. Microstructural investigations of ODS-EUROFER samples implanted to high He fluences reveal a persistent partitioning of introduced gas between different microstructural features. In addition to gas bubbles in the grain bulk, extensive bubble precipitation on extended defects (grain boundaries and dislocations) and precipitates (carbides and oxides) was observed. The relative abundance of bubbles associated with different microstructural features is found to be sensitive to implantation conditions and changes in uncorrelated manner with the variation of implantation parameters. Overall, the main contributions to steel volume expansion (swelling) and the He inventory were from bubbles on grain boundaries and, at lower implantation temperatures and higher fluxes, from bubbles in the grain matrix. However, the preferential He accumulation at grain boundaries does not lead to bubble coalescence and growth of huge grain boundary cavities, without causing high-temperature helium embrittlement. Oxide nanoparticles were found to be efficient centers for helium bubble nucleation, each hosting a single bubble typically noticeably larger than bubbles in other populations. However, their contributions to both swelling and He inventory were estimated to be generally relatively minor as compared to other bubble populations, implying that oxide particle provide no substantial improvement of steel radiation performance. On the contrary, the large bubbles bear the risk of accelerated bubble-to void transition in unfavorable conditions, launching uncontrolled void swelling. The viability of such effect was demonstrated in experiments on simultaneous steel implantation with He and Au ions and quantified using analytical modeling. Under sequential helium and hydrogen implantation into ODS-EUROFER steel, notable increase of hydrogen uptake was observed as compared to oxide-free steel. However, the parameters of He bubble microstructure and, hence, the overall steel radiation resistance were found to be only weakly influenced by hydrogen, in both ODS-EUROFER steel and in Y₂O₃/FeCr bilayer system. Visible hydrogen effects on bubble microstructure were minor and manifested only after the room temperature H implantation. Summing up, ODS steel is shown to be resistant to void swelling up to very high levels of accumulated helium and hydrogen. The presence of high density of nano-oxides is generally beneficial for steel radiation tolerance, but their influence is not as strong as commonly expected. Hydrogen trapping in helium bubbles doesn’t manifest any potential risks for ODS steel radiation tolerance under experimental conditions studied
Owusu-Mensah, Martin. « Understanding the first formation stages of (Y,Ti) nano-oxides in Oxide Dispersion Strengthened (ODS) steels ». Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLS310.
Texte intégralOxide Dispersion Strengthened (ODS) steels, that is steels reinforced with a homogeneous distribution of (Y,Ti) oxide nano-particles, are advanced structural materials for nuclear applications. The oxide particles serve as point defect recombination centres and obstacles to dislocation motion thereby improving radiation resistance and high-temperature strength of these steels making them perfect candidate materials for future fusion and fission nuclear reactors. The conventional fabrication of ODS steels is achieved by mechanical alloying followed by thermomechanical heat treatments. This way of ODS steel production seems complicated to understand the physical mechanisms leading to the precipitation of nano-oxide particles. The kinetics of nanoparticle formation can be much better studied using an alternative technique of nanoparticle growth, namely Ion Beam Synthesis (IBS). This approach has many advantages including the precise control of experimental parameters and the ability to de-correlate various factors contributing to precipitation kinetics. A better knowledge gained in this way would be potentially helpful for optimization of ODS steel production routines. In the course of this PhD study, the IBS approach was applied to investigate the co-precipitation of metal (Y and/or Ti) and oxygen ions implanted into a model Fe-Cr alloy with the composition close to those typical for commercial ODS steels. Following the standard IBS schedule, consisting of ion implantation followed by high-temperature heat treatment, ions of Y, Ti and O at low energies were implanted into high-purity Fe10wt%Cr alloy samples at room temperature. The implanted samples were then annealed at various temperatures ranging from 600 to 1100°C to promote the precipitation of nano-oxide particles. A range of Transmission Electron Microscopy techniques were used to characterize the crystallographic structure and chemical composition of the nanoparticles. The study has been performed following three sets of experiments. First of all, the sequential implantation of Ti and O ions was implemented. Subsequent annealing at temperatures below 1000°C revealed that precipitation of titanium oxide was suppressed. Instead, chromium-rich nano-oxide particles with corundum hexagonal structure were found to precipitate. At sufficiently high temperatures these corundum particles were found to contain certain amount of Ti. Only after annealing at the highest temperature of 1100°C, particles of another type with Ti enriched core and Cr enriched shell were additionally fixed. Secondly, sequential Y and O ion implantation resulted in the formation of probable yttrium-rich oxides at 800°C. Annealing at 1100°C promoted their growth to larger sized yttria (Y₂O₃) particles with a Cr enriched shell. Finally, sequential ion implantation of both metal ions (Y and Ti) was performed, followed by O implantation. The order of metal ion implantation has been found to be crucial for subsequent oxide precipitation at the annealing stage. With the Ti implantation first in the sequence, the precipitation of corundum hexagonal chromium-rich oxide was observed, very similar to the case of Ti and O implantation. In contrast, implantation starting with Y produced yttrium-titanium oxide particles with unidentifiable structure. Summing up, the study has demonstrated the feasibility of the formation of Y, Ti and (Y,Ti) oxides by ion implantation. The thesis presents the detailed characterization of the nanoparticles, as well as the discovered specific features of precipitated particles, such as the presence of orientation relationships between the particles and the FeCr matrix, which was observed even for the case of Cr-rich corundum particles. Finally, the implications of the obtained results, in conjunction with the already known data from the existing literature, for the better understanding of the mechanisms involved in the formation of nano-oxide particles in ODS steels are discussed