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International audience; In the present article, metallic nanoparticles (NPs) used as nanogauges and electron backscattered diffraction (EBSD) are combined to investigate deformation mechanisms of the UR45 N duplex steel. The kinematic fields bring precious details in the evolution of the local deformation of austenitic and ferritic phases. The crystallographic information at the initial stage and in the plastic domain is obtained by the EBSD technique. Strain evolutions in each phase are analyzed. The first strain marks appear in austenite just before the elastoplastic transition. Slip and twinning activities in austenite constitute an important part of the work hardening of the material. The slips in ferrite are visible in the plastic domain and present complex geometry. The role of phase boundaries, which act as strain barrier is highlighted. The incompatibilities of deformations between the two phases modify the deformation mechanism of austenite in comparison with a pure austenitic stainless steel as 316 L. Local interactions between phases during the deformation are analyzed. The strong strain heterogeneities in the plastic domain are analyzed in the kinematic fields. Local evolutions of the deformation are also confronted to the macroscopic behavior of the material.

Thermal barrier coatings (TBC) are multilayered systems comprising a metallic oxidation protection layer or so-called bond coat, a ceramic topcoat, and a thermally grown aluminum oxide developing at the interface. The coating systems fail typically by delamination cracking near this interface, which has a complex three-dimensional morphology influencing the crack path. This study combines laser shock adhesion test to introduce an artificial interfacial crack, known in size and location, and focused ion beam coupled with scanning electron microscopy 3D serial sectioning tomography. Methods for proper segmentation of cracks and adjacent materials and quantitative evaluation of the complex crack system are proposed and applied for analyzing the crack tip region. Finally, derived from the three-dimensional segmentation, a finite element model has been achieved and used for thermal analysis highlighting the crucial role of local damage on thermal conductivity of the TBC.

Electron multipacting and electron cloud have been identified as being the major limiting factors for the beam quality or for the cryogenic system of high-intensity positive particles accelerators. Among conditioning operational techniques and other surface structuration techniques used to decrease the Secondary Electron Yield (SEY) of surfaces, laser surface treatment is a promising method to treat in situ and at atmospheric pressure copper surface of the vacuum chamber. Here, pulsed laser irradiation of copper in parallel lines pattern led to the local ablation and deposition of aggregates of copper particulates on the surface. Tests undertaken at CERN have shown that the modification of the surface morphology by creating roughness at different scales induces a decrease of the SEY by geometrical effects. Nevertheless, the mechanical strength and dust generation of the treated surface have not been addressed yet.In this work, a qualitative analysis of the multi-scale description of the surface morphology was carried out. Scanning Electron Microscopy (SEM), Focused Ion Beam (FIB), Transmission Electron Microscopy (TEM) and Energy Dispersive X-ray Spectroscopy (EDS) were used to investigate morphological characterization such as size and shape of the particulates, chemical composition, metallographic structures and phase transformation on the laser-processed surface.SEM and FIB examinations showed that the surface morphology depends on the local laser energy irradiating the surface and especially, relatively to the ablation threshold. TEM analysis revealed chemical composition and crystalline configuration of the treated material and helped to identify the laser modified and oxidized areas. A variety of superficial structures were observed. Potential vulnerable structures have been identified as oxidized matter redeposited on the ablated near surface. Material continuity and composition play a major role in the mechanical integrity of the generated surface morphology. The adherence of the created structures was assessed analyzing the origin of the dust extracted after mechanical stress.

International audience; The understanding of the mechanical properties at the microstructure scale is a key factor for the material macroscopic behavior comprehension and its appropriate engineering at the scale of the structure. In this study, a new approach which is based on the combination of both nanogauges displacements monitoring and electron backscatter diffraction (EBSD) techniques performed under Scanning Electron Microscope (SEM) during in-situ tensile tests is proposed. Strain evolutions at the microstructure components and the behavior of the material can be compared to the crystallographic data. The approach was applied to austenitic stainless steel 316L specimen in order to bring a proof of concept and put into evidence its potential. Among the information of interest which can be obtained through this technique, one can cite the possibility to highlight the strain initiations in the vicinities of twins and their evolutions during the tensile test or to evidence the strain heterogeneities at the surface of the specimen and its influence over the elongations and rotations of the microstructure components, which tends to be reorganized in order to balance the mechanical stress. Besides, such heterogeneities can be expressed in terms of misorientations and quantified from the EBSD data. The twinning and slip activities can also be correlated to the hardening of the material thanks to this method of characterization. As for its interest for characterizing the plastic domain, the technique can show how some grains may activate more than one slip system. Finally, it has been here demonstrated how complementary and powerful the combination of these two techniques may be considered and how it may give access to a better understanding of the material microstructure properties.

International audience; The present work focuses on the intergranular oxidation of Alloy 600 and its weld material Alloy 82 after exposure in simulated primary water at 340–360 °C during 1000–1400 h. The effects of intergranular chromium carbides, grain boundary character and pre-straining are studied either on industrial heats or model microstructures. Three-dimensional reconstructions of well-chosen grain boundaries are obtained using focused ion beam tomography in a scanning electron microscope. The 3D characterizations show that (1) twin boundaries are less susceptible to oxidation than high-angle grain boundaries; (2) intergranular chromium carbides delay the intergranular oxidation kinetics; (3) the intergranular oxidation depth is quite homogeneous along a given grain boundary except when strain heterogeneity exists in its vicinity, (4) strain heterogeneity tends to accelerate the intergranular oxidation kinetics; and (5) crack initiation in the oxidized grain boundary occurs at the alloy/oxide interface.

International audience; The respective influence of the oxidation and phase transformation on the rumpling of nickel aluminide coatings is reviewed using the thermal treatments in air and Ar atmosphere: β-(Ni,Pt)Al coating deposited on AM1 Ni-base superalloy was subjected to the isothermal and cyclic oxidation at 1100 °C as well as to the thermal cycling in Ar atmosphere. A comparative study of the coating microstructure evolution and surface roughness increase in different conditions suggests that the presence of adherent oxide layer is essential for the rumpling of nickel aluminide coatings on Ni-base superalloys.

International audience; Aluminum (Al) powders with spherical and irregular particle shapes were mixed with two alumina (Al2O3) powders with either a spherical or an angular particle shape to achieve high-performance cold-sprayed coatings onto steel. Two effects of the aluminum particle shape were observed. First, coating microstructure observation showed impinging heterogeneity depending on particle shape. Second, particle jet differences depending on particle morphology were shown by velocity maps. From the latter, SEM and XRD, three effects of the alumina particle shape were also shown, i.e., higher in-flight velocity of angular particles, fragmentation of spherical hollow particles and embedding of alumina particles with aluminum. Numerical simulation of particle impacts was developed to study the densification of Al coating due to Al2O3 addition through elucidation of Al-Al2O3 interaction behavior at the scale of the coating. Al/Al and Al/Al2O3 interfaces were investigated using TEM to understand coating strengthening effects due to alumina addition at the scale of the particle. As a whole, Al and Al2O3 particle shape effects were claimed to explain coating mechanical properties, e.g., microhardness and coating–substrate bond strength. This study resulted in specifying criteria to help cold spray users in selecting powders for their applications, to meet economic and technical requirements.

International audience; Alloy 600 is used in pressurized water reactors (PWRs) but is susceptible to primary water stress corrosion cracking (PWSCC). Intergranular chromium carbides have been found beneficial to reduce PWSCC. Focussed ion beam coupled with scanning electron microscopy (FIB/SEM) 3D tomography has been used to reconstruct the morphology of grain boundary oxide penetrations and their interaction with intergranular Cr carbides in Alloy 600 subjected to a PWR environment. In presence of intergranular Cr carbides, the intergranular oxide penetrations are less deep but larger than without carbide. However, the intergranular oxide volumes normalized by the grain boundary length for both samples are similar, which suggest that intergranular oxidation growth rate is not affected by carbides. Analytical transmission electron microscopy (TEM) shows that the intergranular oxide consists mainly in a spinel-type oxide containing nickel and chromium, except in the vicinity of Cr carbides where Cr 2 O 3 was evidenced. The formation of chromium oxide may explain the lower intergranular oxide depth observed in grain boundaries containing Cr carbides.

International audience; Phase transformation of Pt-modified nickel aluminide coating β-(Ni,Pt)Al into γ′ phase was studied during isothermal and cyclic oxidation at 1100 °C. The transformation occurred with homogeneous β and γ′ phases with chemical compositions depending on oxidation conditions. Cyclic oxidation led to a higher volume fraction of topologically close-packed (TCP) phases formed in the interdiffusion zone and the chemical composition of TCP phases was found to vary with oxidation conditions. This difference in TCP precipitation in the interdiffusion zone for isothermal and cyclic oxidation was suggested to be responsible for different β and γ′ compositions. The experimental observations were discussed using thermodynamic calculations by Thermo-Calc software, and some explanations were given.

International audience; An ordered microporous carbon material was prepared by the nanocasting process using the EMC-2 zeolite (EMT structure type) as a hard template. X-ray diffraction (XRD) and transmission electron microscopy (TEM) revealed long-range ordering in the material that resulted from the negative replication of the host template. The carbon porous network replicating the zeolite structure was modeled by overlapped spherical voids with diameters determined from the XRD pattern that displayed up to six distinct peaks. The surface delimiting the 3D interconnected porosity of the solid has a complex morphology. The pore size distribution calculated from the XRD-derived structural model is characterized by a maximum at 1.04 nm related to the long-range-ordered microporous network. Complementary studies by immersion calorimetry revealed that most of the porosity was characterized by a size above 1.5 nm. These porous features were compared to data resulting from classical analysis (DR, DFT, BET, etc.) of the N2 (77 K) and CO2 (low and high pressure, 273 K) physisorption isotherms. The limitations of these approaches are discussed in light of the pore size distribution consistently determined by XRD and immersion calorimetry measurements.

International audience; Nickel-base alloys are widely used in nuclear Pressurized Water Reactors (PWRs). Most of them have been found susceptible to Stress Corrosion Cracking (SCC) in nominal PWR primary water. The time to initiation depends on the material and is longer for weld metals than for Alloy 600. This study will focus on Alloy 82, which is used in Dissimilar Metal Welds (DMWs). In service, DMWs are either in the as-welded state or have undergone a stress relief treatment. Previous SCC studies showed that the heat treatment reduces significantly the SCC susceptibility of the weld. In this context, this study focuses on the microstructure characterization of the weld in the as-welded state and in the heat-treated state. As chromium content is also a key factor for the SCC susceptibility, welds with low chromium content and medium chromium content were studied. The lower SCC susceptibility of the heat-treated welds was attributed to intergranular Cr23C6 resulting from a combined effect of heat treatment and chromium and carbon contents. These intergranular carbides could explain the better behavior of Alloy 82, compared to other nickel-base alloys.

International audience; This work deals with the study of the irradiation assisted stress corrosion cracking. The purpose is to improve the understanding of irradiation effects on the mechanical behaviour of internal stainless steel structures in PWR environment. The aim is to identify the physical mechanisms responsible for plasticity and damage in relation with the microstructure heterogeneities and to separate the effects induced by the chemical environment to those due to mechanical loading and irradiation. Proton-irradiations are performed in the Michigan Ion Beam Laboratory. Slow Strain Rate Tensile tests are performed both in PWR primary water and under inert atmosphere to study the deformation mechanisms of irradiated samples and their coupling with the environment. To correlate cracking to microstructure, full field analysis are performed, at a microscale, by SEM digital imaging correlation technique coupled with EBSD cartography of the grain orientations after irradiation. Moreover, cracking features are characterized using SEM and TEM.

Zeolite Beta particles with size of 0.1, 0.5 and 1 μm were employed as molds for the synthesis of microporous carbon. After infiltration and pyrolysis of propylene at 800 °C for 2 h, zeolite/carbon composites were obtained and further subjected to acid extraction of the zeolite precursor. The initial zeolite samples, zeolite/carbon composites and carbon replicas were studied by XRD, TG analysis, SEM/TEM, DLS, N2 adsorption measurements and chemical analysis. The experimental data revealed that the carbon replicas faithfully replicate the zeolite morphology and possess higher micropore volume than that of the parent zeolite molds. The use of zeolite molds of different sizes resulted in carbons with fairly different pore structure. Thus, larger (0.5 and 1 μm) zeolite crystals provided replicas with a pore structure possessing mainly micropores, whereas the carbon replication of 0.1 μm zeolite aggregates built of much smaller crystallites resulted in a material with lower micropore volume and substantial contribution of mesopores to the total pore volume. The different pore structure of the latter carbon was found to be a result of the larger external surface area of the nanosized mold, loss of crystallinity during the preparation procedure and the presence of interparticles porosity.

International audience; A wide range of mercaptopropyl-functionalized silica spherical particles of MCM-41 and MCM-48 (M41S family) have been prepared by co-condensation of mercaptopropyl trimethoxysilane (MPTMS) or mercaptopropyl triethoxysilane (MPTES) and tetraethoxysilane (TEOS) precursors in hydroalcoholic medium in the presence of a cationic surfactant as templating agent and ammonia as catalyst. It was possible to control the mesostructure type (hexagonal or cubic) by monitoring the water-to-ethanol ratio and the type of organoalkoxysilane precursor employed. Materials displaying various functionalization levels were obtained by varying the MPTMS or MPTES contents from 3 to 50% in the co-condensation synthesis medium. This gave rise to a wide range of porous solids with approximately the same particle size and morphology but featuring different functionalization levels and various degrees of structural order. They were characterized by X-ray diffraction (XRD), N2 adsorption-desorption isotherms and BET analysis, scanning and transmission electron microscopy, 29Si and 13C solid state nuclear magnetic resonance (NMR), particle size distribution measurements, and elemental chemical analysis. Mercaptopropyl groups were readily incorporated with high yields (>90%) by the co-condensation route. All samples exhibited spherical morphology with similar particle size but both the level of ordering and porosity of solids obtained by co-condensation were found to decrease when increasing the amount of organo-functional groups.