380 results on '"Gentils A"'
Search Results
352. Theoretical and experimental analyses of the synergism in the dielectric strength for C3F8/C2HF5 mixtures.
- Author
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Larin, A. V., Meurice, N., Gentils, F., Fievet, C., and Vercauteren, D. P.
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BREAKDOWN voltage , *ELECTRON-molecule collisions , *DIELECTRICS research , *ELECTRODES , *MIXTURES - Abstract
Two theoretical approaches are applied in order to describe the behavior of the experimental breakdown voltage in C3F8/C2HF5 mixtures. First, available cross section data of the electron-molecule processes are scaled to simulate the dielectric strength (DS) behavior in both C3F8 and C2HF5 gases at the level of the Boltzmann equation (BE) solution corresponding to a homogeneous electric field model. Then, the DS of C3F8/C2HF5 mixtures is evaluated and compared to the experimental breakdown voltage measured using different electrode geometries as sphere/plane type via experimental techniques, i.e., power frequency and negative or positive polarity lightning impulse. Due to the limitation of the BE approach to describe the observed experimental data, the Hunter-Christophorou [J. Appl. Phys. 57, 4377 (1985)] model regarding the positive synergism phenomenon is finally applied. Both models allow us to compare relative values of the “chemical” and “physical” DS components in C3F8/C2HF5 mixtures. [ABSTRACT FROM AUTHOR]
- Published
- 2007
- Full Text
- View/download PDF
353. In situ characterization of irradiation-induced microstructural evolution in urania single crystals at 773 K.
- Author
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Haddad, Yara, Delauche, Lucie, Gentils, Aurélie, and Garrido, Frederico
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IRRADIATION , *MICROSTRUCTURE , *SINGLE crystals , *RADIATION damage , *CHANNELLING radiation - Abstract
Abstract Implantations with low-energy ions (Xe, La) on UO 2 single crystals at 773 K were performed to investigate the role played by both the radiation damage and the incorporation of foreign elements on the matrix destabilisation. The radiation damage was monitored by both in situ RBS-C and in situ TEM during ion irradiation experiments performed at 773 K. RBS-C data shows a similar regular increase of the radiation-induced disorder in crystals for both Xe and La ions followed by a saturation plateau at about 3–4 dpa. An unexpected difference of the value of the saturation plateaus is observed, with a higher value recorded for Xe-irradiated crystals. In situ TEM images show the apparition and evolution of several defects as a function of the ion dose up to 40 dpa, irrespective of the nature of the bombarding ion: 'black dots' defects, dislocation loops and lines, and finally a dislocation network at high dpa. Nanometre-sized gas bubbles were observed at 773 K for the Xe-implanted crystal for doses larger than 3 dpa. Neither precipitate nor cavity were observed on La-implanted crystals. The difference in the saturation plateau as seen by RBS-C can be ascribed to the formation of the Xe aggregates that lead to an increase of the dechannelling yield. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
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354. Understanding helium diffusion in iron: a multiscale modelling method based on the DFT and kinetic Monte Carlo, coupled to TEM and thermo-desorption spectroscopy experiments.
- Author
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Oliveira Cavalcanti, Vinicius, Roques, Jérôme, Gentils, Aurélie, Horlait, Denis, Gilabert, Eric, and Tassan-Got, Laurent
- Subjects
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IRON , *MULTISCALE modeling , *NUCLEAR reactor materials , *MONTE Carlo method , *HELIUM - Abstract
Helium (He) is known to accumulate in vacancies of the steel structure materials of nuclear reactors, forming bubbles that increase in size and eventually cause structural problems, such as embrittlement. Several studies provided insights into the interstitial diffusion of this gas inside the iron matrix. However, much is still unknown about its behaviour. Based on this context, this study proposes a new combined theoretical and experimental multiscale approach made by the same team in a complementary way. It helps to have a global view of the helium diffusion in iron as a function of He content, temperature and structural defect concentration. Firstly, density functional theory has been used to identify the possible helium insertion sites in iron and the possible transitions between them. Then, the kinetic Monte Carlo method was applied to calculate its interstitial diffusion coefficient. It showed that helium swiftly diffuses interstitially in iron. It also tends to be trapped in iron vacancies and accumulate. The chromium and vacancy effects were also investigated. Experimentally, He was ion-implanted in several pure iron and high-purity Fe10wt%Cr samples. An analysis of He behaviour and its diffusion was carried out with transmission electron microscopy (TEM) and thermo-desorption spectroscopy (TDS) techniques. TEM shows the presence of small (∼0.7 nm radius) He bubbles and no significant difference with the presence of Cr. TDS evidences sequential "burst-type" He releases as T is sequentially increased. Based on these observations and inferred from the literature, we propose that He is detrapped and released from the studied materials as a consequence of the decrease in maximum He capacity of the trapping aggregates as T increases. [ABSTRACT FROM AUTHOR]
- Published
- 2023
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355. Experimental diagnostic of an industrial SF6 PTFE confined circuit breaker.
- Author
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Gentils, F., Fleurier, C., Fievet, C., and Le Menn, E.
- Published
- 2000
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356. Optical and electrical investigations on the vacuum arc circuit-breaker.
- Author
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Gherendi, F., Fleurier, C., Rowe, S., and Gentils, F.
- Published
- 1998
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357. Determination of copper concentration in a SF/sub 6/ arc plasma in an electrical circuit breaker.
- Author
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Fleurier, C., Ciobanu, S.S., Hong, D., Gentils, F., and Fievet, C.
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- 1997
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358. In-situ TEM investigation of recovery mechanisms in ion-irradiated ITER-grade tungsten.
- Author
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Iroc, Koray, Terentyev, Dmitry, Van Renterghem, Wouter, Dunatov, Toni, Tadić, Tonči, Klimenkov, Michael, Baumier, Cédric, Gentils, Aurelie, and Schryvers, Dominique
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FLUX pinning , *TUNGSTEN , *DISLOCATION loops , *NEUTRON irradiation , *TRANSMISSION electron microscopy , *THERMAL stability - Abstract
The annealing of irradiation defects in tungsten was investigated under in-situ observations conducted using transmission electron microscopy (TEM). ITER-specification tungsten was exposed to heavy-ion irradiation by 10 MeV Au+ ions to 0.5 and 1 dpa at room temperature to generate defects. Subsequently, the thermal stability and recovery mechanisms of the generated defects are investigated by in-situ TEM at 600 °C, 800 °C, 900 °C and 1000 °C. The obtained TEM data are used to visualize and quantify the defect characteristics such as loops and voids as well as for observing the evolution of the microstructure and defect diffusion/recovery mechanisms. Focus is made on specific spatial phenomena such as loop-loop interaction, loop-dislocation and loop-grain boundary decoration, loop pinning, entanglement, formation of raft and transformation of loops into a dislocation network. The obtained results are in line with earlier obtained data for pure recrystallized tungsten, still, present results provide important information such as radiation-induced defect characteristics and recovery mechanisms under high temperature for the ITER-specification tungsten. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
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359. Study of helium diffusion in yttria: A multiscale approach based on the density functional theory and kinetic Monte Carlo, with transmission electron microscopy and thermo-desorption spectroscopy.
- Author
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Cavalcanti, Vinicius Oliveira, Roques, Jérôme, Horlait, Denis, Gilabert, Eric, Riant, Guillaume, Colombeau-Bedos, Thomas, Clavier, Nicolas, and Gentils, Aurélie
- Subjects
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TRANSMISSION electron microscopy , *DENSITY functional theory , *HELIUM , *YTTRIUM oxides , *GRAIN size , *DISPERSION strengthening - Abstract
A known issue for future nuclear reactors is helium accumulation inside the steel structure materials, responsible for structural issues such as embrittlement and cracking. One possible solution is using new types of reinforced steel, such as oxide dispersion strengthened (ODS) steel. It consists of adding oxide nanoparticles to the Fe-based material, especially yttrium oxide (yttria, Y 2 O 3), improving its properties. Therefore, one first step is understanding the helium diffusion inside this system. Very little is known about helium inside yttria, with most studies being theoretical ones. Based on this context, this work proposes a combined theoretical and experimental multiscale approach to investigate helium diffusion inside yttria. The theoretical approach starts with the density functional theory, used to model the atomic yttria cell and determine helium insertion sites. The transitions between the sites were described using the Nudged Elastic Bond (NEB) method. Kinetic Monte Carlo was then employed to obtain the interstitial diffusion coefficient expression for the first time for this material. It showed a limited diffusion at temperatures below 600 K, which may indicate a tendency for He to be blocked in the oxide. Then, the charged vacancies were explored. It showed that the vacancy further reduces helium diffusion. Finally, it was demonstrated that helium spreads across different vacancies and interstitial sites. The experimental part involved implanting helium ions at 50 keV in samples with nanometric or micrometric grains. Then, the specimens were characterised with transmission electron microscopy (TEM) and thermo-desorption spectroscopy (TDS) techniques. TEM did not evidence detectable bubbles even at the highest studied fluence (1 × 1016 cm−2). The TDS highlighted different mechanisms for helium diffusion and the grain size's role, providing a novel model for diffusion coefficient calculation based on interstitial diffusion. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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360. courrier des lecteurs: Monaco et Raza.
- Author
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GENTILS, ISA
- Abstract
A letter to the editor is presented in response to an article in a previous issue which concerns the French's lack of interest in abstract paintings created by Indian artist Syed Haider Raza.
- Published
- 2011
361. Synthesis of Nano-Oxide Precipitates by Implantation of Ti, Y and O Ions in Fe-10%Cr: Towards an Understanding of Precipitation in Oxide Dispersion-Strengthened (ODS) Steels.
- Author
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Jublot-Leclerc, Stéphanie, Owusu-Mensah, Martin, Borodin, Vladimir A., Ribis, Joël, Largeau, Ludovic, Schoell, Ryan, Kaoumi, Djamel, Descoins, Marion, Mangelinck, Dominique, and Gentils, Aurélie
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DISCONTINUOUS precipitation , *MATRIX effect , *OXIDES , *IONS , *ION implantation , *CHROMIUM oxide - Abstract
The properties of oxide dispersion-strengthened steels are highly dependent on the nature and size distribution of their constituting nano-oxide precipitates. A fine control of the processes of synthesis would enable the optimization of pertinent properties for use in various energy systems. This control, however, requires knowledge of the precise mechanisms of nucleation and growth of the nanoprecipitates, which are still a matter of debate. In the present study, nano-oxide precipitates were produced via the implantation of Y, Ti, and O ions in two different sequential orders in an Fe-10%Cr matrix that was subsequently thermally annealed. The results show that the oxides that precipitate are not necessarily favoured thermodynamically, but rather result from complex kinetics aspects related to the interaction between the implanted elements and induced defects. When Y is implanted first, the formation of nanoprecipitates with characteristics similar to those in conventionally produced ODS steels, especially with a core/shell structure, is evidenced. In contrast, when implantation starts with Ti, the precipitation of yttria during subsequent high-temperature annealing is totally suppressed, and corundum Cr2O3 precipitates instead. Moreover, the systematic involvement of {110} matrix planes in orientation relationships with the precipitates, independently of the precipitate nature, suggests matrix restriction effects on the early stages of precipitation. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
362. Influence of injected ions on α' formation under ion irradiation in Oxide Dispersion Strengthened Steels.
- Author
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Loyer-Prost, Marie, Jublot-Leclerc, Stéphanie, Saleh-Afif, Marie-José, Ribis, Joël, and Gentils, Aurélie
- Subjects
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ATOM-probe tomography , *ION implantation , *DISPERSION strengthening , *PHASE separation , *STEEL - Abstract
Oxide Dispersion Strengthened (ODS) steels hold great promise for applications in next generation reactors. Under irradiation, a phase separation α/ α' can occur within the Fe-Cr matrix of ODS steels that can alter their mechanical properties. This work presents, for the first time, the characteristics of α' precipitates enhanced by ion irradiation at 400 °C and examines the influence of the implanted ions. Far from the implanted region, α' is reported in significant density while at the implanted peak, the α' density is considerably reduced. This suggests that ion implantation either reduces the fraction of α' phase formed after irradiation or delays considerably its formation. Through atom probe tomography analysis and comparison with existing literature, the low impact of the damage rate and fluence on the α' formation in ODS steels is highlighted. Interestingly, the efficiency of ballistic mixing of α' appears to be less pronounced in ODS steels than in Fe-Cr systems. [Display omitted] [ABSTRACT FROM AUTHOR]
- Published
- 2025
- Full Text
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363. Microstructural modifications induced by He implantation at elevated temperature in AlN.
- Author
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Jublot-Leclerc, S., Bouhali, G., Bachelet, C., Pallier, F., Largeau, L., Declémy, A., and Gentils, A.
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HIGH temperatures , *POINT defects , *TRANSMISSION electron microscopy , *X-ray diffraction - Abstract
The elastic strain and damage build-ups induced by 50 keV He implantations at elevated temperature in (0001)AlN were studied using a combination of X-ray diffraction, transmission electron microscopy and elastic recoil detection analysis experiments. No long-range migration of He atoms occurs up to 700°C. The point defect recombination is found to be enhanced with the increase of implantation temperature. When He concentration exceeds a determined temperature-dependent threshold, the stabilization of vacancies through the formation of He-vacancy clusters of critical size strongly enhances the interstitial concentration and elastic strain in proportion with the local He concentration. Above this threshold, for a critical He concentration that decreases from several at% at room temperature to a few tenths of at% at 700°C, bubbles form and induce a strong increase of disorder. Specific features observed at 700°C, including the systematic superimposition of bubble clusters with basal stacking faults, suggest the triggering between 550 and 700°C of a mechanism promoting disorder, which is discussed. • The mobility of point defects is increased from RT to 550°C, and from 550 to 700°C. • XRD is used to determine threshold He concentrations related to He-V clustering. • These thresholds are ascribed to the formation of He-V clusters of critical size. • Peculiar bubble growth and bubble cluster-BSF relationships are observed at 700°C. • A mechanism promoting disorder is triggered between 550 and 700°C. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
364. In situ TEM study of the stability of nano-oxides in ODS steels under ion-irradiation
- Author
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Lescoat, M-L., Ribis, J., Gentils, A., Kaïtasov, O., de Carlan, Y., and Legris, A.
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DISPERSION strengthening , *MOLECULAR structure , *MICROSTRUCTURE , *METALLIC oxides , *FUSION reactors , *TRANSMISSION electron microscopy , *NANOSTRUCTURED materials , *FERRITIC steel , *MARTENSITIC stainless steel , *POINT defects - Abstract
Abstract: Oxide Dispersion Strengthened (ODS) ferritic–martensitic steels are considered for nuclear applications as structural components for fusion or fission reactors. To ensure good performances in service, the stability under irradiation of the microstructure and especially of Y–Ti–O nanoclusters have to be assessed. In situ Transmission Electron Microscopy has been performed to follow the Y–Ti–O nano-oxides dispersed in a Fe18Cr1W0.3Ti+0.6Y2O3 ODS material under ion-irradiation at 500°C. Microstructural examinations using bright and dark field mode showed that Y–Ti–O nano-precipitates (5nm) are still present after irradiation up to 45dpa. However, some larger oxides seem to be more affected by irradiation at 45dpa (creation of point defects, interface and shape modification). [Copyright &y& Elsevier]
- Published
- 2012
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365. Numerical simulation of the porous filter properties for the internal arc mollifying effects
- Author
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Rochette, D., Clain, S., Gentils, F., Wild, J., and Bussière, W.
- Subjects
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COMPUTER simulation , *FILTERS (Mathematics) , *PROTOTYPES , *MATHEMATICAL models , *POROSITY , *GAS flow - Abstract
Abstract: A mathematical model and numerical experiments of pressure wave impacts with a porous medium are presented to simulate the valve burst out of a medium voltage switchgear and to evaluate the protection filter efficiency. A simplified one-dimensional gas flow model in porous medium with variable porosity is used. To solve numerically the governing equations, we employed the numerical method presented in Rochette et al. (2005) to take into account the non-conservative term P(∂ϕ/∂x). Three sets of test are performed to study several filter prototypes. The objective is to provide a filter which does not produce a high reflected wave and cools enough the ejected hot gas. We first consider filters with variable porosity and simulate the interaction with an incident pressure wave, then we consider two types of granular material to characterize their incidence on the flow and finally, we simulate two different fluid flows (air and SF6) going through the porous medium. [ABSTRACT FROM AUTHOR]
- Published
- 2011
- Full Text
- View/download PDF
366. On the numerical simulation of the diffuse arc in a vacuum interrupter.
- Author
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Langlois, Y., Chapelle, P., Jardy, A., and Gentils, F.
- Subjects
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VACUUM circuit breakers , *MAGNETIC fields , *IONS , *ELECTRONS , *VACUUM switches , *CATHODES - Abstract
A 2D two-fluid numerical model is developed for the description of the diffuse arc in a vacuum interrupter under the possible influence of an axial magnetic field (AMF). This model incorporates the energy balance equations for both ions and electrons and takes into account the three components of the self-generated magnetic field. The possibility of both supersonic (at low current density) and subsonic (at high current density) plasma flow regimes is considered. Data from the literature are used to specify the values of the plasma parameters near the cathode, and the boundary conditions on the anode boundary rely on a simplified model of the anode sheath. Simulation results are presented for both ion flow regimes, with special attention to the current and plasma flow features. It is shown that there is always a contraction of the current flow, whereas the dynamics of the ions throughout the interelectrode gap is strongly influenced by their flow regime near the cathode. Finally, the influence of various operating parameters (presence of an AMF, gap length) on the current constriction at the anode is discussed. [ABSTRACT FROM AUTHOR]
- Published
- 2011
- Full Text
- View/download PDF
367. Current constriction of high-current vacuum arc in vacuum interrupters.
- Author
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Lijun Wang, Shenli Jia, Ling Zhang, Dingge Yang, Zongqian Shi, Gentils, Francois, and Jusselin, Benoît
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VACUUM arcs , *MAGNETOHYDRODYNAMICS , *SIMULATION methods & models , *MAGNETIC fields , *MAGNETIC properties , *PHYSICS - Abstract
Compared with previous paper [L. Wang et al., J. Appl. Phys. 100, 113304 (2006)], higher-current vacuum arc is simulated and analyzed based on magnetohydrodynamics model, and current constriction phenomenon in arc column is mainly paid attention to and analyzed in this paper. According to simulation results, it can be found that significant current constriction only appears near anode regions for lower-current vacuum arc. However, with the increase of arc current, current constriction also appears near the cathode side, and with the further increase of arc current, current constriction near the cathode side can become more significant than that near the anode side. The current constriction near the cathode side can be mainly caused by very high current level. The increase of axial magnetic field (AMF) strength will inhibit current constriction in the whole arc column. For influence of AMF distribution, saddle-shaped distributed AMF can more efficiently inhibit current constriction of arc column than bell-shaped AMF. The phenomenon of current constriction near the cathode side has also been found by many experiments, which also can verify the correctness of simulation results. [ABSTRACT FROM AUTHOR]
- Published
- 2008
- Full Text
- View/download PDF
368. In situ TEM observations of ion irradiation damage in boron carbide.
- Author
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Victor, Guillaume, Pipon, Yves, Moncoffre, Nathalie, Bérerd, Nicolas, Esnouf, Claude, Douillard, Thierry, and Gentils, Aurélie
- Subjects
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BORON carbides , *TRANSMISSION electron microscopy , *NEUTRON absorbers , *ION beams , *CRYSTAL orientation - Abstract
Abstract This paper presents an in situ Transmission Electron Microscopy (TEM) study of the damage formation process in ion-irradiated boron carbide used as neutron absorber for fast nuclear reactors. We focused our experiment on the damage induced by 1 MeV gold ions irradiation performed on the JANNuS-Orsay in situ dual ion beam TEM facility. The effects of the crystallographic orientation and the temperature (RT, 500 °C and 800 °C) on the ion-irradiated boron carbide structure were studied. The different steps of damage formation leading to amorphization are described. At RT, material amorphization is observed at a damage dose threshold around 7.5 displacements per atom (dpa). It is also shown that no amorphization occurred when irradiation is performed at 500 °C or 800 °C up to the highest fluence studied (3 × 1015 ions cm−2, i.e. 7.6 dpa). [ABSTRACT FROM AUTHOR]
- Published
- 2019
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- View/download PDF
369. Cavity nucleation and growth in dual beam irradiated 316L industrial austenitic stainless steel.
- Author
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Jublot-Leclerc, S., Li, X., Legras, L., Fortuna, F., and Gentils, A.
- Subjects
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AUSTENITIC stainless steel , *NUCLEATION , *TRANSMISSION electron microscopes , *METAL microstructure , *CHEMICAL stability - Abstract
Thin foils of 316L were simultaneously ion irradiated and He implanted in situ in a Transmission Electron Microscope at elevated temperatures. The resulting microstructure is carefully investigated in comparison with previous single ion irradiation experiments with a focus on the nucleation and growth of cavities. Helium is found to strongly enhance the nucleation of cavities in dual beam experiments. On the contrary, it does not induce more nucleation when implanted consecutively to an in situ ion irradiation but rather the growth of cavities by absorption at existing cavities, which shows the importance of synergistic effects and He injection mode on the microstructural changes. In both dual beam and single beam experiments, the characteristics of the populations of cavities, either stabilized by He or O atoms, are in qualitative agreement with the predictions of rate theory models for cavity growth. The evolutions of cavity population as a function of irradiation conditions can be reasonably well explained by the concept of relative sink strength of cavities and dislocations and the resulting partitioning of defects at sinks, or conversely recombination when either of the sinks dominates. The dislocations whose presence is a prerequisite to cavity growth in rate theory models are not observed in all studied conditions. In this case, the net influx of vacancies to cavities necessary to their growth and conversion to voids is believed to result from free surface effects, and possibly also segregation of elements close to the cavity surface. In any studied condition, the measured swelling is low, which is ascribed to the dilution of gaseous atoms among a high density of cavities as well as a high rate of point defect recombination and loss at traps. This high rate of recombination enhanced when dislocations are absent appears to result in the formation of overpressurized He bubbles. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
370. Stability of β″ nano-phases in Al-Mg-Si(-Cu) alloy under high dose ion irradiation.
- Author
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Flament, Camille, Ribis, Joël, Garnier, Jérôme, Serruys, Y., Leprêtre, F., Gentils, A., Baumier, C., Descoins, M., Mangelinck, D., Lopez, A., Colas, K., Buchanan, K., Donnadieu, P., and Deschamps, Alexis
- Subjects
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ATOMIC displacements , *ALLOYS , *TRANSMISSION electron microscopy , *ATOM-probe tomography , *RADIATION - Abstract
The microstructure of a 6061-T6 Al alloy subjected to ion irradiation at 95 and 165 displacements per atom (dpa) has been evaluated by transmission electron microscopy and atom-probe tomography. The initial microstructure of the alloy is dominated by needle-shaped β″ precipitates. After 95 dpa irradiation, the β″ precipitates display a slight lattice distortion and are partially dissolved, together with the formation of a new phase. After 165 dpa irradiation, the β″ precipitates are completely dissolved, the new phase has grown and a high density of clusters rich in Mg, Si, Cu and Cr is observed. The determination of ballistic versus radiation enhanced diffusion coefficients shows that enhanced diffusion is predominant for β” dissolution. The formation and growth of the new particles may be caused by radiation induced segregation. Solute drag by vacancies or mixed dumbbell interstitials migration could explain the diffusion of some elements as Si or Cr towards the new particles. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
371. Microstructure of Au-ion irradiated 316L and FeNiCr austenitic stainless steels.
- Author
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Jublot-Leclerc, S., Li, X., Legras, L., Lescoat, M.-L., Fortuna, F., and Gentils, A.
- Subjects
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MICROSTRUCTURE , *AUSTENITIC stainless steel , *TRANSMISSION electron microscopy , *GOLD , *METAL ions , *IRON compounds - Abstract
Thin foils of 316L were irradiated in situ in a Transmission Electron Microscope with 4 MeV Au ions at 450 °C and 550 °C. Similar irradiations were performed at 450 °C in FeNiCr. The void and dislocation microstructure of 316L is found to depend strongly on temperature. At 450 °C, a dense network of dislocation lines is observed in situ to grow from black dot defects by absorption of other black dots and interstitial clusters whilst no Frank loops are detected. At 550 °C, no such network is observed but large Frank loops and perfect loops whose sudden appearance is concomitant with a strong increase in void density as a result of a strong coupling between voids and dislocations. Moreover, differences in both alloys microstructure show the major role played by the minor constituents of 316L, increasing the stacking fault formation energy, and possibly leading to significant differences in swelling behaviour. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
372. TEM study of the nucleation of bubbles induced by He implantation in 316L industrial austenitic stainless steel.
- Author
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Jublot-Leclerc, S., Lescoat, M.-L., Fortuna, F., Legras, L., Li, X., and Gentils, A.
- Subjects
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DISCONTINUOUS precipitation , *HELIUM , *ION implantation , *BUBBLES , *TRANSMISSION electron microscopy , *AUSTENITIC stainless steel , *QUANTITATIVE research , *TEMPERATURE effect - Abstract
10 keV He ions were implanted in-situ in a TEM into thin foils of 316L industrial austenitic stainless steel at temperatures ranging from 200 to 550 °C. As a result, overpressurized nanometric bubbles are created with density and size depending strongly on both the temperature and fluence of implantation. An investigation on their nucleation and growth is reported through a rigorous statistical analysis whose procedure, including the consideration of free surface effects, is detailed. In the parameter range considered, the results show that an increase of fluence promotes both the nucleation and growth of the bubbles whilst an increase of temperature enhances the growth of the bubbles at the expense of their nucleation. The confrontation of resulting activation energies with existing models for bubble nucleation enables the identification of the underlying mechanisms. In spite of slight differences resulting from different conditions of implantation among which the He concentration, He production rate and He/dpa ratio, it appears that the dominating mechanisms are the same as those obtained in metals in previous studies, which, in addition to corroborating literature results, shows the suitability of in-situ TEM experiments to simulate the production of helium in nuclear materials. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
373. Modeling of helium bubble nucleation and growth in austenitic stainless steels using an Object Kinetic Monte Carlo method.
- Author
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De Backer, A., Adjanor, G., Domain, C., Lescoat, M.L., Jublot-Leclerc, S., Fortuna, F., Gentils, A., Ortiz, C.J., Souidi, A., and Becquart, C.S.
- Subjects
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AUSTENITIC stainless steel , *HELIUM content of metals , *BUBBLES , *NUCLEATION , *CHEMICAL kinetics , *MONTE Carlo method - Abstract
Implantation of 10 keV helium in 316L steel thin foils was performed in JANNuS-Orsay facility and modeled using a multiscale approach. Density Functional Theory (DFT) atomistic calculations [1] were used to obtain the properties of He and He-vacancy clusters, and the Binary Collision Approximation based code MARLOWE was applied to determine the damage and He-ion depth profiles as in [2,3] . The processes involved in the homogeneous He bubble nucleation and growth were defined and implemented in the Object Kinetic Monte Carlo code LAKIMOCA [4] . In particular as the He to dpa ratio was high, self-trapping of He clusters and the trap mutation of He-vacancy clusters had to be taken into account. With this multiscale approach, the formation of bubbles was modeled up to nanometer-scale size, where bubbles can be observed by Transmission Electron Microscopy. Their densities and sizes were studied as functions of fluence (up to 5 × 10 19 He/m 2 ) at two temperatures (473 and 723 K) and for different sample thicknesses (25–250 nm). It appears that the damage is not only due to the collision cascades but is also strongly controlled by the He accumulation in pressurized bubbles. Comparison with experimental data is discussed and sensible agreement is achieved. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
374. Modeling gas-driven microstructural evolution in ODS-EUROFER steel by high dose helium and hydrogen ion implantation
- Author
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Emelianova, Olga, Laboratoire de Physique des 2 Infinis Irène Joliot-Curie (IJCLab), Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Institute of Nuclear Physics and Engineering (INPhE), The National Research Nuclear University MEPhI (Moscow Engineering Physics Institute) [Moscow, Russia], Université Paris-Saclay, National Research Nuclear University MEPhI (Moscou), Aurélie Gentils, Maria Ganchenkova, Vladimir Borodin, and STAR, ABES
- Subjects
Oxide nanoparticles ,Hydrogen/helium ,Oxide dispersion strengthened steels (ODS steels) ,Modeling and simulation ,Implantation d'ions ,Microscopie électronique en transmission (TEM) ,Modélisation et simulation ,Hydrogène / hélium ,[PHYS.COND.CM-MS] Physics [physics]/Condensed Matter [cond-mat]/Materials Science [cond-mat.mtrl-sci] ,Gonflement ,Ion implantation ,Aciers renforcés par dispersion d'oxydes (aciers ODS) ,[PHYS.COND.CM-MS]Physics [physics]/Condensed Matter [cond-mat]/Materials Science [cond-mat.mtrl-sci] ,Transmission electron microscopy (TEM) ,[PHYS.COND]Physics [physics]/Condensed Matter [cond-mat] ,Swelling ,[PHYS.COND] Physics [physics]/Condensed Matter [cond-mat] ,Nanoparticules d'oxyde - Abstract
Oxide 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., Les aciers ferritiques-martensitiques renforcés par dispersion d'oxydes (ODS) sont des matériaux de structure de haute performance pour les futures installations nucléaires de fission et de fusion. Un problème important pour la performance de ces aciers sous irradiation est leur résistance aux effets néfastes des gaz de transmutation, l'hélium et l'hydrogène, avec une attention particulière aux effets liés à la forte densité de nanoparticules d'oxyde. L'objectif de la thèse est une étude systématique et fondamentale de l’évolution de la microstructure induite par les gaz légers dans les aciers ODS ferritiques-martensitiques en fonction de la teneur en gaz accumulée, du taux d'endommagement et de la température, en accordant une attention particulière au rôle des nanoparticules d'oxyde. L'approche expérimentale utilisée a consisté à saturer des échantillons avec différentes quantités d'hélium et d'hydrogène, par implantation ionique à JANNuS-Orsay, dans des conditions bien contrôlées. Le matériau de référence utilisé était l'acier ODS-EUROFER. Les modifications microstructurales accompagnant l'accumulation de gaz ont été révélées par microscopie électronique à transmission. Pour une meilleure compréhension des mécanismes d’interaction de l’hélium avec les nanoparticules d’oxyde, les expériences ont été complétées par des implantations ioniques dans un système modèle de couches minces Y₂O₃/FeCr, et par une modélisation analytique et numérique pertinente. Cependant, leurs contributions au gonflement sont généralement relativement mineures par rapport aux autres populations de bulles. Au contraire, les grosses bulles comportent le risque d'une transition accélérée d’une bulle à une cavité dans des conditions défavorables, ce qui provoque un gonflement non contrôlé des cavités. La viabilité d'un tel effet a été démontrée dans des expériences d'implantation d’ions He et d’irradiation d’ions Au simultanées, et quantifiée à l'aide d'une modélisation analytique. Lors de l'implantation séquentielle d'hélium et d'hydrogène dans l'acier ODS-EUROFER, une augmentation notable de l'absorption d'hydrogène a été observée par rapport à l'acier ne contenant pas d’oxyde. Cependant, la résistance globale à l’irradiation de l'acier n'a été que faiblement influencée par l'hydrogène, aussi bien dans l'acier ODS-EUROFER que dans le système modèle Y₂O₃/FeCr. Les effets visibles de l'hydrogène sur la microstructure des bulles étaient mineurs et ne se manifestaient qu'après l'implantation d’H à température ambiante. En résumé, l’acier ODS s’avère résistant au gonflement jusqu’à des niveaux très élevés d’hélium et d’hydrogène accumulés. La présence de nano-oxydes à haute densité est généralement bénéfique pour la tolérance à l’irradiation de l'acier, mais leur influence n'est pas aussi forte que celle attendue. Le piégeage de l’hydrogène dans les bulles d’hélium ne présente aucun risque potentiel pour la tolérance à l’irradiation de l’acier ODS dans les conditions expérimentales étudiées.
- Published
- 2020
375. On the numerical simulation of the diffuse arc in a vacuum interrupter
- Author
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Gentils, F [Schneider Electric Industries SAS, Usine 38V, ZAC Champ Saint Ange, F-38050 Grenoble Cedex 9 (France)]
- Published
- 2011
- Full Text
- View/download PDF
376. Identification of the Nitrogen Split Interstitial (N-N)N in GaN.
- Author
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von Bardeleben, H. J., Cantin, J. L., Gerstmann, U., Scholle, A., Greulich-Weber, S., Rauls, E., Landmann, M., Schmidt, W. G., Gentils, A., Botsoa, J., and Barthe, M. F.
- Subjects
- *
NITROGEN , *ELECTRON paramagnetic resonance , *IRRADIATION , *PERSONAL identification numbers , *SPECTRUM analysis - Abstract
Combining electron paramagnetic resonance, density functional theory, and positron annihilation spectroscopy (PAS), we identify the nitrogen interstitial defect in GaN. The isolated interstitial is unstable and transforms into a split interstitial configuration (N-N)N, It is generated by particle irradiation with an introduction rate of a primary defect, pins the Fermi level at Ec - 1.0 eV for high fluences, and anneals out at 400 °C. The associated defect, the nitrogen vacancy, is observed by PAS only in the initial stage of irradiation. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
377. Helium behavior in α-SiC ceramics investigated by NRA technique
- Author
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Sauvage, T., Carlot, G., Martin, G., Vincent, L., Garcia, P., Barthe, M.F., Gentils, A., and Desgardin, P.
- Subjects
- *
HELIUM , *ION implantation , *SILICON carbide , *DIFFUSION - Abstract
Abstract: The mechanisms involved in helium migration in α-SiC are investigated through the evolution of its microstructure and of the concentration profiles following annealing at 1300°C/30min for fluences of 1 and 5×1015 3Hecm−2 and a He implantation energy of 500keV. Helium profiling is performed using the 3He(d,α)1H NRA technique with an improved detection limit of 5atppm. The NRA and TEM techniques clearly show that depending on the initial fluence, a proportion of the helium is trapped within the grain and a part of the helium is released. Analysis of the helium profile changes after annealing enabled to determine a value of the volume diffusion coefficient close to (8±1)×10−17 m2 s−1 for both fluences studied. [Copyright &y& Elsevier]
- Published
- 2007
- Full Text
- View/download PDF
378. Understanding the first formation stages of (Y,Ti) nano-oxides in Oxide Dispersion Strengthened (ODS) steels
- Author
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Owusu-Mensah, Martin, Centre de Sciences Nucléaires et de Sciences de la Matière (CSNSM), Université Paris-Sud - Paris 11 (UP11)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS), Université Paris Saclay (COmUE), Aurélie Gentils, and Centre National de la Recherche Scientifique (CNRS)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université Paris-Sud - Paris 11 (UP11)
- Subjects
Oxide nanoparticles ,Précipitation ,Recuit thermique ,Thermal annealing ,Ion beam synthesis ,Aciers renforcés par dispersion d'oxydes (ODS) ,Precipitation ,Nano-oxydes ,[PHYS.NEXP]Physics [physics]/Nuclear Experiment [nucl-ex] ,Oxide Dispersion Strengthened (ODS) steels ,Alliages Fe-Cr ,[SPI.MAT]Engineering Sciences [physics]/Materials ,Microscopie électronique en transmission (MET) ,Implantation ionique ,Ion implantation ,Synthèse par faisceaux d’ions ,Transmission Electron Microscopy (TEM) ,Fe-Cr alloys - Abstract
Oxide 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.; Les aciers appelés ODS (pour Oxide Dispersion Strengthened), renforcés par une dispersion homogène de nano-oxydes, sont des matériaux de structure avancés pour les futurs réacteurs nucléaires de fusion et de fission. En effet ces nano-oxydes, à base d’Y et Ti, servent comme centres de recombinaison de défauts ponctuels et d'obstacles aux mouvements des dislocations, améliorant de ce fait leur résistance aux radiations et aux températures élevées. La fabrication conventionnelle des aciers ODS est réalisée par broyage mécanique suivi de traitements thermo-mécaniques, et ne permet pas facilement de comprendre les mécanismes physiques conduisant à la précipitation des nano-oxydes, ce qui serait potentiellement utile pour optimiser leur production. La cinétique de formation de ces nano-oxydes peut être étudiée en utilisant une technique alternative, à savoir la synthèse par faisceaux d’ions, qui présente de nombreux avantages, notamment le contrôle précis des paramètres expérimentaux et la possibilité de décorréler divers facteurs contribuant à la cinétique de précipitation. Au cours de cette thèse, cette technique a été utilisée pour étudier la coprécipitation d'ions métalliques (Y et/ou Ti) et d'oxygène implantés dans un alliage modèle Fe-Cr de composition proche de celle typique des aciers ODS commerciaux. Des ions de Y, Ti et O à basse énergie ont été implantés dans des échantillons d'alliage Fe10wt%Cr de haute pureté à température ambiante. Les échantillons implantés ont ensuite été recuits à diverses températures entre 600 à 1100°C pour favoriser la précipitation de nano-oxydes, conformément au principe de cette technique. La microscopie électronique à transmission a été utilisée pour caractériser la structure cristallographique et la composition chimique des nano-oxydes formés lors de trois séries d'expériences. Tout d'abord, l'implantation séquentielle d'ions Ti et O a été mise en œuvre. Un recuit ultérieur a révélé qu’il n’y avait pas de précipitation d'oxyde de titane jusqu’à des températures inférieures à 1000°C, mais la présence de nano-oxydes riches en chrome avec une structure hexagonale de type corundum, qui contiennent une certaine quantité de Ti à des températures suffisamment élevées. Ce n’est qu’après le recuit à 1100°C que des nano-oxydes d’un autre type à cœur enrichi en Ti et coquille enrichie en Cr ont également été observés. Deuxièmement, l'implantation séquentielle d’ions Y et O a entraîné la formation à 800°C de nano-oxydes probablement riches en yttrium. Le recuit à 1100°C a favorisé la croissance des particules identifiées comme étant des nano-oxydes d’yttrium avec une coquille enrichie en Cr. Enfin, une implantation ionique séquentielle de deux ions métalliques (Y et Ti) a été réalisée, suivie d'une implantation d’O. L'ordre d'implantation des ions métalliques s'est révélé crucial pour la précipitation de nano-oxydes lors du recuit ultérieur. Lors de la séquence avec une implantation de Ti en premier, une précipitation d'oxyde riche en chrome de structure corundum hexagonale a été observée, très similaire au cas de l'implantation d’ions Ti et O. En revanche, la séquence avec une implantation d’ions Y en premier a produit des nano-oxydes d'yttrium-titane qui possèdent une structure non identifiable. En résumé, l’étude a démontré la faisabilité de la formation de nano-oxydes de Y, Ti et (Y, Ti) par implantation ionique. La thèse présente la caractérisation détaillée de ces nano-oxydes, ainsi que certaines de leurs caractéristiques spécifiques, telles que la présence de relations d'orientation entre les nano-oxydes et la matrice FeCr, qui ont été observées même dans le cas de nano-oxydes de type corundum riches en Cr. Enfin, les résultats obtenus, combinées avec les données de la littérature, sont discutées pour une meilleure compréhension des mécanismes impliqués dans la formation des nano-oxydes dans les aciers ODS.
- Published
- 2019
379. Helium bubble nucleation and growth in alloy HT9 through the use of in situ TEM: Sequential he-implantation and heavy-ion irradiation versus dual-beam irradiation.
- Author
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Duemmler, Kai, Zheng, Ce, Baumier, Cedric, Gentils, Aurelie, and Kaoumi, Djamel
- Subjects
- *
HEAVY ions , *DISCONTINUOUS precipitation , *ION implantation , *IRRADIATION , *TRANSMISSION electron microscopy , *NUCLEAR density - Abstract
The formation of He bubbles in Ferritic/Martensitic steel HT9 is investigated through the use of in situ Transmission Electron Microscopy coupled with He implantation and heavy ion irradiation. Of particular interest is the effect of increasing He appm/dpa ratio on the formation and growth of the bubbles, as well as the effect of the sequential order of ion irradiation i.e. He-pre-implantation followed by heavy-ion irradiation versus true dual-beam irradiation. The role of He is discussed. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
380. Radiation-Induced Sharpening in Cr-Coated Zirconium Alloy.
- Author
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Ribis J, Wu A, Guillou R, Brachet JC, Baumier C, Gentils A, and Loyer-Prost M
- Abstract
To improve the safety of nuclear power plants, a Cr protective layer is deposited on zirconium alloys to enhance oxidation resistance of the nuclear fuel cladding during both in-service and hypothetical accidental transients at High Temperature (HT) in Light Water Reactors. The formation of the Cr
2 O3 film on the coating surface considerably helps in reducing the oxidation kinetics of the zirconium alloy, especially during hypothetic Loss of Coolant Accident (LOCA). However, if the Cr coating is successful to increase the oxidation resistance at HT of the zirconium substrate, for in-service conditions, under neutron irradiation, Cr desquamation has to be avoided to guarantee a safe use of the Cr-coated zirconium alloys. Therefore, the adhesion properties have to be maintained despite the structural defects created by sustained neutron irradiation in the reactor environment. This paper proposes to study the behavior of the Zircaloy-Cr interface of a first generation Cr-coated material during a specific in situ ion irradiation. As deposited, the Cr-coated sample presents a f.c.c. C15 Laves-type intermetallic phase at the interface with off-stoichiometric composition. After irradiation and for the specific conditions applied, this interfacial phase has significantly dissolved. Energy Dispersion Spectroscopy revealed that the dissolution was accompanied by a counterintuitive "sharpening" effect.- Published
- 2022
- Full Text
- View/download PDF
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