Au cours de cette thèse, nous avons étudié in situ la solidification du silicium à l’aide de l'imagerie X-synchrotron. Les deux techniques utilisées lors de la solidification sont la radiographie et la diffraction de Bragg, elles permettent de caractériser: la dynamique des mécanismes de croissance, la cinétique de croissance, la nucléation et la compétition de grains, la déformation du réseau cristallin et les champs de contraintes liés aux dislocations. Ces observations sont combinées avec des caractérisations ex situ pour étudier l'orientation cristallographique, les déformations du réseau cristallin ainsi que les concentrations d'impuretés légères telles que le carbone et l'oxygène.La complémentarité de ces techniques permet d'étudier et de mieux comprendre : les phénomènes physiques liés à la formation de la structure de grain finale. Les résultats concernant la cinétique de croissance de l'interface solide-liquide et des facettes {111}, l'établissement de la structure de grain, l'importance du maclage, l'effet des impuretés légères, le champ de contrainte lié à la croissance et la compétition de grains et les dislocations sont discutés dans le manuscrit. / During this thesis, we studied in situ the solidification of silicon with X-synchrotron imaging. The two techniques used during solidification are radiography and Bragg diffraction and they allow characterizing: dynamic growth mechanisms, growth kinetics, grain nucleation and competition, lattice deformation and dislocation related strain fields. These observations are combined with ex situ characterizations to study the crystallographic orientation, the deformations of the crystal lattice as well as the concentrations of light impurities such as carbon and oxygen. The complementarity of these techniques makes it possible to study and to better understand: the physical phenomena related to the formation of the final grain structure. Results concerning the growth kinetics of the solid-liquid interface and of the {111} facets, the establishment of the grain structure, the importance of twinning, the effect of light impurities, the strain field related to growth and grain competition and dislocations are discussed in the manuscript.

Ce travail de thèse porte sur la déformation bi-axiale contrôlée de nano-composites W/Cu en couches minces déposées sur des substrats polyimides. La nano-structuration est obtenue par stratification de deux matériaux immiscibles (W et Cu) par pulvérisation ionique avec contrôle de la taille des grains au sein du film mince par contrôle de l'épaisseur selon la direction decroissance du film. Nous avons développé une procédure permettant de caractériser le comportement mécanique des échantillons à deux échelles différentes. L'essai de traction biaxial est couplé à la diffraction des rayons X (déformation microscopique) et à la corrélation d'images numériques (déformation macroscopique). Nous avons utilisé une machine de tractionbi-axiale développée dans le cadre d’un projet ANR sur la ligne de lumière DiffAbs du synchrotron SOLEIL. Elle permet de contrôler les contraintes dans des films minces supportés par des substrats polyimides. La confrontation des résultats obtenus par ces deux techniques dans le domaine d'élasticité a montré que la déformation est intégralement transmise via l’interfacefilm - substrat. La seconde étape de notre travail a consisté à étudier les déformations du nanocomposite W/Cu au-delà du domaine d’élasticité. Nous avons mis en évidence trois domaines de déformation associés à différents mécanismes de déformation. La limite d'élasticité du nanocomposite W/Cu a été déterminée en comparant la déformation élastique du film mince à la déformation macroscopique du substrat. Enfin, l'étude de la limite d'élasticité du nanocomposite W/Cu pour différents ratios de force a révélé un comportement fragile du nanocomposite W/Cu. / This thesis focuses on the biaxial deformation of W/Cu nanocomposite thin films deposited on polyimide substrates. The grain size in the thin film is controlled by stratification of two immiscible materials (W and Cu) employing sputtering techniques. We developed a procedure to characterize the mechanical behavior of samples at two different scales. A biaxial tensile test is coupled to X-ray diffraction (microscopic deformation) and digital image correlation (macroscopic deformation) techniques. We used a biaxial tensile setup developed in the framework of an ANR project on the DiffAbs beamline at synchrotron SOLEIL allowing forthe control of stresses in thin films supported by polyimide substrates. By comparing the strains obtained by these two techniques, the applied strain is determined to be transmitted unchanged in the elastic domain through the film - substrate interface. The second part of our work was to study the deformation of W/Cu nanocomposite beyond the elastic range. We have highlighted three domains of deformation associated with different deformation mechanisms. The elastic limit of the W/Cu nanocomposite was determined by comparing the elastic deformation of the thin film to the macroscopic deformation of the substrate. Finally, the elastic limit of W/Cu nanocomposite was studied for different load ratios. The overall results emphasized the brittle behavior of these nanocomposites.

Ce travail de thèse propose d'étudier les effets de taille et de microstructure sur les propriétés mécaniques de films minces d'or nanostructurés déposés sur des substrats flexibles lors d'essais de traction bi-axiale. Les couches minces d'or sont déposées sur du polyimide par pulvérisation ionique, technique qui permet de contrôler la taille des grains selon la direction de croissance dans les films minces en contrôlant l'épaisseur de ces derniers. Nous avons ensuite réalisé des expériences de déformation in-situ sur ces couches minces grâce à la machine de traction bi-axiale installée sur la ligne de lumière DiffAbs du synchrotron SOLEIL, source de rayons X intense qui permet de mesurer par diffraction les déformations dans les films minces polycristallins. La première étape de ce travail a été d'effectuer des expériences de traction bi-axiale pour des chargements dits « pas à pas » en imposant différents ratios de force sur deux séries de couches minces d’or d'épaisseurs différentes afin d'étudier la limite d'élasticité en fonction du chemin de chargement choisi et de tracer une surface de charge pour les deux séries d'échantillons d'or étudiés. La deuxième étape de ce travail a consisté à valider un mode de chargement dit « continu » en comparant les propriétés mécaniques d'une même série d'échantillons d'or obtenus avec ces deux types de chargements : « pas à pas » et « continu ». Une fois validé, nous avons réalisé des expériences de traction bi-axiale sur différentes séries d'échantillons d'or possédant différentes tailles grains et architecture afin de mettre en évidence un effet de taille sur les propriétés mécaniques de films minces nanométriques. / The main purpose of this thesis is to study the size and microstructure effects on the mechanical response of gold nanostructured thin films deposited on flexible substrates during biaxial tensile tests. Gold thin films are deposited onto polyimide substrates by sequenced ion sputtering technique in order to control the grain size in the growth direction. We have carried out in situ deformation experiments using the biaxial tensile device installed on the diffractometer of the DiffAbs beamline at synchrotron SOLEIL (Saint-Aubin, France), an intense X-rays source which allows to determine applied strains in polycrystalline thin films thanks to x-ray diffraction measurements. In a first step, we performed tensile biaxial tests for different load ratio using “step by step” procedure on two series of gold thin films showing different thicknesses in order to study the mechanical response analyzing the yield surface that can be extracted with the biaxial device. In a second step, we validated a continuous loading procedure which allows gaining a factor of 10 in the time frame. Validation is made by comparing the mechanical properties of two series of gold thin films investigated using “step by step” loading and “continuous” loading. After validation of the continuous loading procedure, tensile biaxial tests have been performed on different series of gold thin films with different grain size and architecture in order to put in highlight a size effect on the mechanical behavior of nanolayered thin films.

Afin d'optimiser les performances des circuits intégrés, l’industrie de la micro et nanotechnologie mène d'intenses recherches sur la miniaturisation à l'échelle sub-22nm de leurs principaux constituants que sont les transistors MOS. La réduction de la taille de grille atteint néanmoins des limites qui rendent problématique le contrôle du canal. L'une des approches les plus prometteuses pour contourner ce dilemme et ainsi poursuivre la miniaturisation des futurs nœuds technologiques, consiste au développement des transistors d’architectures 3D (Trigate ou FinFET). La mise au point de telles structures requiert une caractérisation de plus en plus fine, surtout à une étape clé de leur élaboration, qui est celle du dopage par implantation ionique. Du fait des faibles profondeurs implantées, l'analyse par diffusion d'ions de moyenne énergie (MEIS) est tout à fait adaptée pour quantifier les implants et évaluer la conformité du dopage grâce à sa bonne résolution en profondeur (0.25 nm). Néanmoins, les dimensions de la sonde (0.5 × 1 mm2) étant très supérieures à celles des motifs, il nous a fallu développer un protocole d’analyse propre à de telles architectures. Les échantillons étudiés dans le cadre de cette thèse sont des systèmes modèles. Ils sont constitués de réseaux de lignes de silicium (Si) 3D, formées par gravure lithographique par faisceaux d’électrons (e-beam) sur des plaques 300 mm de types silicium sur isolant (SOI). Le dopage a été réalisé à une énergie de 3 keV par implantions conventionnelle (ou beam line) et immersion plasma (PIII).L’analyse des spectres MEIS des implants insérés dans chaque facette des motifs a été possible grâce aux simulations 3D types Monte-Carlo effectuées avec le logiciel PowerMEIS. Nous avons ainsi développé une nouvelle méthode adaptée à la caractérisation du dopage 3D. Les mesures ont montré que, contrairement à la méthode PIII, la dose implantée par la méthode conventionnelle correspond à celle visée. Cependant la distribution des dopants introduits au sein des nanostructures par les deux méthodes de dopage n’est pas uniforme. Dans les échantillons implantés par PIII, on a observé une importante concentration des dopants aux sommets des motifs et un faible dopage des flancs. Ceci étant moins marqué dans celui implanté par la méthode conventionnelle. En corrélant les techniques de Microscopie Electronique en Transmission (MET), d’analyses par rayons x synchrotron et MEIS, nous avons également pu déterminer les dimensions des zones implantées ainsi que celles des zones cristallines dans les réseaux de lignes gravées.L'exploitation de la technique MEIS en mode canalisation a permis une évaluation complète des couches non gravées. L’investigation des endommagements post – dopage dans les régions cristallines non implantées ont été menées toujours avec la même technique MEIS. Les résultats ont révélé une importante influence de la méthode d’implantation et la température sur les défauts et les déformations dans le cristal. L’origine des anomalies au sein des échantillons a ainsi été identifiée en corrélant les mesures MEIS et celles par spectrométrie de masse des ions secondaires en temps de vol (ToF-SIMS). / With the aim of optimizing the performances of integrated circuits (ICs), the nanotechnology industry is carrying out intense research activities on the miniaturization at the sub-22 nm scale of their main constituents: the MOS transistors. Nevertheless, the shrinking of the gate size has reached the limits that make the control of the channel problematic. One of the most promising approaches to circumvent this dilemma and thus further the miniaturization of the future technological nodes, is the development of transistors of 3D architecture (Trigate or FinFET). The elaboration of such nanostructures requires increasingly fine characterization tools precisely at a key stage of their fabrication, namely the ion implantation doping. Given the ultra-shallow implantation depths, the medium energy ion scattering (MEIS) analysis technique is suitable for quantifying the implants and evaluating the doping conformity thanks to its good depth resolution (0.25 nm). However, the dimensions of the beam (0.5×1 mm2) being by far larger than those of the patterns, we had to develop an analysis protocol dedicated to such architectures. The samples studied in the framework of this thesis are considered as model systems. They are constituted of 3D silicon (Si) Fin – shaped line gratings, etched on the 300 mm wafers of silicon on insulator (SOI) types by using the electron beam (e-beam) lithography. The doping has been carried out at an energy of 3 keV by using the conventional (or beam line) and plasma immersion ion implantation (PIII) methods.The analyses s of the MEIS spectra of the dopants implanted into each part of the patterns were possible thanks to the 3D Monte-Carlo simulations performed with the PowerMEIS software. We have thus developed a new method suitable for the characterization of the 3D doping. The measurements have shown that, contrarily to the PIII method, the dose implanted by the conventional method is as targeted. However, the distribution of the dopants inserted within the nanostructures by using the two doping methods is not uniform. In the PIII implanted samples, a large dopants' focusing at the tops of the patterns and low sidewalls' doping have been observed. This is less marked in the one implanted by the conventional method. By correlating the Transmission Electron Microscopy (TEM), synchrotron x – ray analyses and MEIS, we have also determined the dimensions of the implanted and crystal areas of the line gratings.The exploitation of the MEIS technique in channeling mode has permitted the full assessment of the impacts of the implantation in the non-etched layers. The investigations of the crystal qualities in the non-implanted areas were carried out with the same technique. The results show that the temperature conditions have a considerable influence on the defects and lattice deformations. The origin of the anomalies in the samples has thus been identified by correlating the MEIS and Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) measurements.

Nous étudions l'effet thermo-électrique et les phénomènes qui en résultent, forces et les courants thermoélectriques (TEC) sous l'action d'un champ magnétique externe imposé lors de la solidification d'alliages métalliques. Nous avons utilisé des simulations numériques, des observations directes et des examens de laboratoire. L'interaction entre les courants thermo-électriques et le champ magnétique externe lors de la solidification se produit des forces électromagnétiques et donc un écoulement du métal liquide. Le résultat est nommé effet magnétique thermoélectrique (TEME). Les formulations de TEC, les forces et les équations gouvernant les écoulements TEM sont donnés. Afin de mieux prouver l'existence de la TEME, des expériences par méthode d'imagerie à rayons X menées au synchrtron ont été utilisées pour observer in-situ et en temps réel l'action directe des forces et les mouvements TEM pendant la solidification directionnelle des alliages Al-Cu. Nous avons montré la cohérence raisonnable entre les calculs analytiques et des simulations numériques qui ont exécuté avec les mêmes conditions de traitement. En outre, la capacité des écoulements thermo-électriques à influer sur la microstructure lors de la solidification directionnelle sont expérimentalement évaluées dans les autres cas en réalité. La solidification directionnelle d'une seule phase de formation des alliages Al-Cu sous divers champs magnétiques montre que les écoulements TEM sont capables de modifier la forme de l'interface liquide-solide conduisant à des morphologies différentes. L'effet le plus intense se produit dans différents champs magnétiques pour différentes morphologies, en effet, le champ magnétique élevé est nécessaire pour la morphologie a une plus petite longueur typique. Ceci est en accord avec le comportement des vitesses de TEM qui varient avec les champs magnétiques imposés ainsi que les différentes échelles de longueur typique. Cette variation est confirmée par des simulations numériques 3D. Nous montrons que les dendrites primaires et à l'avant de la phase eutectique, peuvent être modifiés par les mouvements TEM et les forces de TEM dans le solide pour améliorer la croissance de la phase de Al2Cu facettes primaire pendant la solidification des Al-40wt%Cu hypereutectiques. Le mécanisme de renforcement de la croissance de la phase facettes Al2Cu est confirmé par la transmission électronique observation au microscope, et la raison de la formation de la structure de croissance de couple de Al-26wt% Cu alliages est vérifiée par le test de l'analyse thermique différentielle. Ainsi, nous pouvons affirmer que le champ magnétique élevé facilite la formation de la structure de la croissance de couple pour hypoeutectiques alliages Al-Cu, et favorise la croissance de la phase Al2Cu primaire pour hypereutectiques Al-Cu alliages. / We have investigated the thermoelectric magnetic (TEM) forces and flows resulting from the interaction between the internal thermoelectric currents (TEC) and the imposed external magnetic field during solidification. Numerical simulations, direct observations and experimental examinations were undertaken. As the natural phenomenon, TEC was discovered almost 200 years ago, therefore, our introduction begins from then on. It is shown that the interaction between TEC and external magnetic field during solidification in the cont put forth new interesting phenomena in the context of a rising field named Electromagnetic Processing of Materials. After that, it is discussed how the TEC appear and the TEM effect (TEME, referring to both TEM forces and flows) behaves at the liquid-solid interface in directional solidification under external magnetic field. Meanwhile, formulations of TEC, TEM forces and flows are given, and numerical simulations of TEME are performed to visually display the TEM forces and flows. In order to further prove the existence of TEME, in situ synchrotron X-ray imaging method was used to observe the direct resultant of TEM forces and flows during directionally solidifying the Al-Cu alloys. The observations show reasonable consistency with the analytical calculations and numerical simulations performed with the same process conditions. Except confirmation the existence of TEME, its abilities to affect the microstructure during directional solidification are experimentally investigated in the more realistic cases. The single phase forming Al-Cu alloys are directionally solidified under various magnetic fields, which shows that TEM flows are capable to modify the shape of liquid-solid interface, and the most intensive affect occurs under different magnetic fields for different interface morphologies. Indeed, the smaller the typical length of the morphology is the higher the magnetic field is needed. This agrees with the estimating regulation of the velocity of TEM flows changing with magnetic fields for different typical length scales, and is confirmed by 3D numerical simulations. Directional solidification of multiphase forming Al-Cu alloys under various magnetic fields shows that the mushy zone length (distance between the front of primary dendrites and eutectic phases) varies with the magnetic fields, which can be attributed to the redistribution of rejected solutes by TEM flows. In addition, apparent enhanced growth of the primary faceted Al2Cu phase is founded when Al-40wt%Cu alloys are solidified under sufficient high magnetic fields, this should be ascribed to the TEM forces acting on the solid because strains are able to lead the formation of defects and thus benefit to the growth of faceted phase. This is confirmed by comparison of the dislocations in samples solidified without and with a 10T magnetic field via transmission electron microscopy observation. In another aspect, an almost entire couple growth structure is achieved when Al-26wt%Cu alloys are directionally solidified under a 4T magnetic field, which can be explained by the effect of high magnetic field on changing the nucleation temperature and growth velocity of each phase. Moreover, the differential thermal analysis test on the nucleation temperature of both α-Al and eutectic phases verified this explanation. Therefore, we conclude that high magnetic field facilitates the formation of couple growth structure for hypoeutectic Al-Cu alloys, reversely, enhances the growth of primary dendrite for hypereutectic Al-Cu alloys.

No description available.

Additive manufacturing (AM) introduces high variability in the microstructure and defect distributions, compared with conventional processing techniques, which introduces greater uncertainty in the resulting fatigue performance of manufactured parts. As a result, qualification of AM parts poses as a problem in continued adoption of these materials in safety-critical components for the aerospace industry. Hence, there is a need to develop precise and accurate, physics-based predictive models to quantify the fatigue performance, as a means to accelerate the qualification of AM parts. The fatigue performance is a critical requirement in the safe-life design philosophy used in the aerospace industry. Fatigue failure is governed by the loading conditions and the attributes of the material microstructure, namely, grain size distribution, texture, and defects. In this work, the crystal plasticity finite element (CPFE) method is employed to model the microstructure-based material response of an additively manufactured Ni-based superalloy, Inconel 718 (IN718). Using CPFE and associated experiments, methodologies were developed to assess multiple aspects of the fatigue behavior of IN718 using four studies. In the first study, a CPFE framework is developed to estimate the critical characteristics of porosity, namely the pore size and proximity that would cause a significant debit in the fatigue life. The second study is performed to evaluate multiple metrics based on plastic strain and local stress in their ability to predict both the modes of failure as seen in fractography experiments and estimate the scatter in fatigue life due to microstructural variability as obtained from fatigue testing. In the third study, a systematic analysis was performed to investigate the role of the simulation volume and the microstructural constraints on the fatigue life predictions to provide informed guidelines for simulation volume selection that is both computationally tractable and results in consistent scatter predictions. In the fourth study, validation of the CPFE results with the experiments were performed to build confidence in the model predictions. To this end, 3D realistic microstructures representative of the test specimen were created based on the multi-modal experimental data obtained from high-energy diffraction experiments and electron backscatter diffraction microscopy. Following this, the location of failure is predicted using the model, which resulted in an unambiguous one to one correlation with the experiment. In summary, the development of microstructure-sensitive predictive methods for fatigue assessment presents a tangible step towards the adoption of model-based approaches that can be used to compliment and reduce the overall number of physical tests necessary to qualify a material for use in application.

<div>The mechanical behaviors of different kinds of biological tissues, including muscle tissues, cortical bones, cancellous bones and skulls, were studied under various loading conditions to investigate their strain-rate sensitivities and loading-direction dependencies. Specifically, the compressive mechanical behaviors of porcine muscle were studied at quasi-static (<1/s) and intermediate (1/s─10^2/s) strain rates. Both the compressive and tensile mechanical behaviors of human muscle were investigated at quasi-static and intermediate strain rates. The effect of strain-rate and loading-direction on the compressive mechanical behaviors of human frontal skulls, with its entire sandwich structure intact, were also studied at quasi-static, intermediate and high (10^2/s─10^3/s) strain rates. The fracture behaviors of porcine cortical bone and cancellous bone were investigated at both quasi-static (0.01mm/s) and dynamic (~6.1 m/s) loading rates, with the entire failure process visualized, in real-time, using the phase contrast imaging technique. Research effort was also focused on studying the dynamic fracture behaviors, in terms of fracture initiation toughness and crack-growth resistance curve (R-curve), of porcine cortical bone in three loading directions: in-plane transverse, out-of-plane transverse and in-plane longitudinal. A hydraulic material testing system (MTS) was used to load all the biological tissues at quasi-static and intermediate loading rates. Experiments at high loading rates were performed on regular or modified Kolsky bars. Tomography of bone specimens was also performed to help understand their microstructures and obtain the basic material properties before mechanical characterizations. Experimental results found that both porcine muscle and human muscle exhibited non-linear and strain-rate dependent mechanical behaviors in the range from quasi-static (10^(-2)/s─1/s) to intermediate (1/s─10^2/s) loading rates. The porcine muscle showed no significant difference in the stress-strain curve between the along-fiber and transverse-to-fiber orientation, while it was found the human muscle was stiffer and stronger along fiber direction in tension than transverse-to fiber direction in compression. The human frontal skulls exhibited a highly loading-direction dependent mechanical behavior: higher ultimate strength, with an increasing ratio of 2, and higher elastic modulus, with an increasing ratio of 3, were found in tangential loading direction when compared with those in the radial direction. A transition from quasi-ductile to brittle compressive mechanical behaviors of human frontal skulls was also observed as loading rate increased from quasi-static to dynamic, as the elastic modulus was increased by factors of 4 and 2.5 in the radial and tangential loading directions, respectively. Experimental results also suggested that the strength in the radial direction was mainly depended on the diploë porosity while the diploë layer ratio played the predominant role in the tangential direction. For the fracture behaviors of bones, straight-through crack paths were observed in both the in-plane longitudinal cortical bone specimens and cancellous bone specimens, while the cracks were highly tortuous in the in-plane transverse cortical bone specimens. Although the extent of toughening mechanisms at dynamic loading rate was comparatively diminished, crack deflections and twists at osteon cement lines were still observed in the transversely oriented cortical bone specimens at not only quasi-static loading rate but also dynamic loading rate. The locations of fracture initiations were found statistical independent on the bone type, while the propagation direction of incipient crack was significantly dependent on the loading direction in cortical bone and largely varied among different types of bones (cortical bone and cancellous bone). In addition, the crack propagation velocities were dependent on crack extension over the entire crack path for all the three loading directions while the initial velocity for in-plane direction was lower than the other two directions. Both the cortical bone and cancellous bone exhibited higher fracture initiation toughness and steeper R-curves at the quasi-static loading rate than the dynamic loading rate. For cortical bone at a dynamic loading rate (5.4 m/s), the R-curves were steepest, and the crack surfaces were most tortuous in the in-plane transverse direction while highly smooth crack paths and slowly growing R-curves were found in the in-plane longitudinal direction, suggesting an overall transition from brittle to ductile-like fracture behaviors as the osteon orientation varies from in-plane longitudinal to out-of-plane transverse, and to in-plane transverse eventually.</div>