京都大学 / 新制・課程博士 / 博士(工学) / 甲第23157号 / 工博第4801号 / 新制||工||1751(附属図書館) / 京都大学大学院工学研究科材料工学専攻 / (主査)教授 辻 伸泰, 教授 乾 晴行, 教授 安田 秀幸 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Serious issues including solidification porosity, columnar grains, and large grain sizes are common during fusion-based metal additive manufacturing due to the inherent melting and solidification that occurs during printing. In recent years, a high-temperature, rapid plastic deformation technique called additive friction stir deposition (AFSD) has shown great promise in overcoming these issues. Because the deposited material stays in the solid state during printing, there are no melting and solidification events and the process can result in as-printed material that is fully-dense with equiaxed, fine grains. As AFSD is an emerging process, developing an understanding of the synergy between material deformation and the resultant microstructure evolution, especially the strain magnitude, its influence on dynamic microstructure evolution, and material flow details, is imperative for the full implementation of AFSD. Therefore, the purpose of this work is to investigate the severe plastic deformation in AFSD through complementary studies on the concurrent evolution of shape and microstructure during the deposition of dissimilar aluminum alloys. In this work, we systematically study (1) the entire deposition via dissimilar cladding along with (2) specific volumes within the deposited layer via embedded tracers printed at varied processing parameters. X-ray computed tomography and electron backscatter diffraction are employed to visualize the complex shape of the deposits and understand the microstructure progression. Investigation of dissimilar cladding of homogeneous AA2024 feed-rods onto an AA6061 substrate establishes a working understanding of the mechanisms related to material flow and microstructure evolution across the whole deposit (macroscopic shape evolution) as well as at the interface between the deposit and the substrate. Variations in tooling and rotation rate affect the interfacial features, average grain size, and depth of microstructural influence. The non-planar and asymmetric nature of AFSD on the macro-scale is revealed and a maximum boundary of deposited material is established which gives a frame of reference for the next material flow study within the deposition zone. An understanding of the mesoscopic morphological evolution and concurrent dynamic microstructure evolution of representative volumes within the deposition zone is determined by comparing depositions of hybrid feed-rods (AA6061 matrix containing an embedded tracer of AA2024). Samples were printed with and without an in-plane velocity to compare initial material feeding to steady-state deposition. Variations in initial tracer location and tool rotation rate/in-plane velocity pairs affect the final morphology, intensity of mixing, and microstructure of the deposited tracer material. The tracer material undergoes drastic mesoscopic shape evolution from millimeter-scale cylinders to long, curved micro-ribbons. There is simultaneous grain refinement in AA2024 via geometric dynamic recrystallization during initial material feeding, after which the grain size remains relatively constant at a steady-state size. The lower bound of strain is estimated based on extrusion, torsion, and shear-thinning factors. The step-by-step mesoscopic deformation and microstructure evolution is further elucidated by characterizing depositions of hybrid feed-rods with a series of embedded tracers. The AFSD tooling is stopped quickly at the end of the deposition with a quench applied to "freeze" the sample. X-ray computed tomography reveals multiple intermediate morphologies including the progression from a cylinder to a tight spiral, to a flattened spiral shape, and to a thin disc. EBSD mapping shows that a refined microstructure is formed soon after the material leaves to tool head with areas off the centerline reaching a fully recrystallized state more quickly. The findings from this work summarize the current understanding of the link between material deformation and microstructure evolution in AFSD. Hopefully these first fundamental studies on the co-evolution of material flow and grain structure during AFSD can inspire future work, especially in the area of heterogeneous multi-material printing. / Doctor of Philosophy / Additive friction stir deposition (AFSD) is a new metal 3D printing process that uses friction to heat up and deposit materials rather than using a laser to melt the material into place. This is beneficial since it avoids problems that come from melting and solidification (e.g., porosity, hot cracking, residual stresses, columnar grains). Since AFSD is such a new technology, an understanding of some of the fundamental processing science is needed in order to predict and control the performance of the resultant parts. This is because the processing of a material affects its structure (at multiple scales, for example macro-, micro-, atomic) which then affects the properties a material will exhibit which, finally, dictates the performance of the overall part. Therefore, the purpose of this work is to explore how the feed material is transformed and deposited into the final layer after printing and to link the original processing conditions to the resultant structure. To investigate the interface between the deposited layer and the substrate, we use a simple feed-rod of one aluminum alloy (AA2024) and deposit it onto a substrate of another aluminum alloy (AA6061). To look at just one small volume within the deposited layer, we use a hybrid feed-rod that is mostly AA6061 except for small cylinders of AA2024 that are placed either in the center or on the edge of the feed-rod so that we can track the AA2024. Printing these feed-rods under different processing conditions will help us understand the connection between processing and structure. Using a characterization technique called X-ray computed tomography we can visualize a 3D representation of the final position for the AA2024 material. In order to evaluate the structure on the micro-scale, a characterization technique called electron backscatter diffraction is used to show the individual grains of our metal. The main contributions of this work are as follows: 1) a lower bound of strain is estimated for AFSD, 2) various intermediate deformation steps are captured for the tracer cylinders including a progression from cylinder to multiple spiral shapes to a thin disc to long ribbons, 3) these deformation steps are linked to different microstructures, and 4) changing the tool geometry and other processing parameters significantly alters the range of shapes and microstructures developed in the deposited material. These findings bring us closer to a fully controllable system as well as sparking some interesting areas for future research because of the complex shapes we observed. These results could lead to the customization and optimization of 3D spirals, ribbons, etc. designed for a certain application.

Aluminum alloys have increasing applications in construction and transportation industries. Both 5xxx-series (Al-Mg) and 6xxx-series (Al-Mg) alloys are frequently used in marine construction because of their light weight, high strength, and corrosion resistance. One of the major concerns regarding the marine application of aluminum alloys is their mechanical performance in fire scenarios. The material strength may be degraded due to both thermal and mechanical damage during fire exposure. This work emphasizes the stress-induced mechanical (physical) damage and its impact on the residual (post-fire) performance of 5083-H116 and 6061-T651 aluminum alloy. Thermo-mechanical tests were performed at various temperatures and stresses to study the stress-induced damage at induced plastic creep strain levels. Unstressed thermally exposed and thermo-mechanically damaged samples were examined to separate the stress-induced microstructural damage. The stress-induced microstructural damage primarily manifests itself as dynamic recovery at low creep temperatures, while cavitation, dynamic recrystallization and dynamic precipitation (in Al6061) are the types of damage developed in the high creep strains at high exposure temperatures. Different creep mechanisms are also studied for both Al5083 and Al6061. The post-fire mechanical response at room temperature after thermo-mechanical damage was investigated with reference to the damaged microstructure present in the material. Residual material strengths based on deformed cross sectional area after the creep test were calculated to provide insight into how microstructural damage affects the post-fire material performance. The competing effects of strength degradation caused by cavitation and strengthening due to grain elongation and subgrain refinement were investigated. Engineering residual material strengths calculated based on the original cross sectional area prior to creep tests were also studied to provide guidance for structural design. / Ph. D.

Yes / In this study, a comparison of different methods to predict drug−polymer solubility was carried out on binary systems consisting of five model drugs (paracetamol, chloramphenicol, celecoxib, indomethacin, and felodipine) and polyvinylpyrrolidone/vinyl acetate copolymers (PVP/VA) of different monomer weight ratios. The drug−polymer solubility at 25 °C was predicted using the Flory−Huggins model, from data obtained at elevated temperature using thermal analysis methods based on the recrystallization of a supersaturated amorphous solid dispersion and two variations of the melting point depression method. These predictions were compared with the solubility in the low molecular weight liquid analogues of the PVP/VA copolymer (N-vinylpyrrolidone and vinyl acetate). The predicted solubilities at 25 °C varied considerably depending on the method used. However, the three thermal analysis methods ranked the predicted solubilities in the same order, except for the felodipine−PVP system. Furthermore, the magnitude of the predicted solubilities from the recrystallization method and melting point depression method correlated well with the estimates based on the solubility in the liquid analogues, which suggests that this method can be used as an initial screening tool if a liquid analogue is available. The learnings of this important comparative study provided general guidance for the selection of the most suitable method(s) for the screening of drug−polymer solubility. / The Irish Research Council and Eli Lilly S.A. through an Irish Research Council Enterprise Partnership Scholarship for C.M.B., in part by The Royal Society in the form of Industrial Fellowship awarded to G.A., and in part by a research grant from Science Foundation Ireland (SFI) under Grant Number SFI/12/RC/2275 (for A.M.H., L.T., K.P., and A.K.).

Mg-alloys, despite being the lightest structural metallic materials, find limited applications due to their poor workability, which is due to the hcp structure that does not provide sufficient number of independent slip systems for compatible deformation. Workability improves with the increase in the deformation temperature, when non-basal slip starts playing a larger role in deformation. Efforts were made to improve the workability through control of texture, grain refinement and alloying. Alloying activates non-basal slip by decreasing the critical resolved shear stress (CRSS) on non-basal planes or by promoting cross slip through an increase in the stacking fault energy (SFE) on basal planes. In this thesis, the effect of Li addition to the most widely used wrought Mg-alloy AZ31 on its workability is examined. Plastic deformation behaviour of a series of AZ31-Li alloys with temperature, T, and strain rates, ε , as variables was studied, so as to identify the optimum Li content that results in highly workable alloy. The T and ε combinations that are best suited for hot deformation of these alloys were also identified through processing maps and microstructural analysis. First, deformation behaviour of the base AZ31 is examined in detail. Compression tests were carried out, with T ranging between 150 and 400 °C and at ranging from 10-3 to 102 s-1, covering entire hot working range of the alloy. The results suggest that the deformation behaviour of AZ31 could be partitioned into three temperature regimes. In low T regime, twinning played an important role. It changes the orientation and increases hardening rate, θ (given by dσ/dε where σ and ε are true stress and strain respectively); material exhibits macroscopic flow localization and cracking along twin boundaries. The onset of twinning was examined in detail by examining the local maxima before ϵpeak strain in plot between d2σ/dε2 vs. ε. Twinning was found to occur at all the deformation conditions. Dynamic recrystallization (DRX) was observed at temperatures above 250 °C whereas deformation at low T (< 250 °C) led to extensive twinning at all . ε . At intermediate T of 250-300 °C, plastic strains tend to localize near grain/twin boundaries, confining DRX only to these regions. Increase in T promotes non-basal slip, which, in turn, leads to uniform deformation; DRX too becomes uniform. The dependence of critical stress (σc) for the onset of DRX and peak flow stress (σp) on Zener-Hollomon parameter (Z) indicates that these stresses increase with Z. Activation energy (Q) for the deformation of AZ31 was estimated at peak stress and steady state conditions. High values of Q (150-200 kJ/mol) indicate cross slip as the rate controlling mechanism, at the peak, in the stress-strain responses. For steady state, Q corresponds to lattice/grain boundary diffusion (90-150 kJ/mol). Next, the effect of Li on deformation behaviour of AZ31 was examined. In addition to AZ31 without any Li (0Li), three alloys 1 (1Li), 3 (3Li) and 5 (5Li) wt% Li were prepared with the aid of a specially designed set-up for melting and casting of Li containing alloys. Experimental results on homogenized alloys show that 1Li alloy’s overall response is similar to that of 0Li alloy, but 3Li and 5Li alloys exhibit distinctly different deformation behaviour. Li addition facilitates cross slip by increasing SFE on basal planes, thus leading to change in the deformation mechanism of the alloy. Increased softening due to cross slip decreases θ and also the twin density at low ϵ (<10-2 s-1). During deformation at low ϵ and low T, high Li alloys reveal cavities along the grain boundaries in contrast to cracking along twin boundaries that was observed in AZ31. In the intermediate T range, high Li alloys reveal the presence of a small mantle, which can be attributed to the increased cross slip with increasing Li. In fact, Li addition was found to restrict DRX and promote dynamic recovery (DRY). As ϵ increases in this T regime deformation becomes more homogeneous and twinning occurs extensively in high Li alloys. This results in remarkable increase in dσ/dε (θ) in these alloys and DRX was predominantly seen at twinned regions. At high ϵ -T regime, where non-basal slip and twinning occur uniformly, DRX is observed throughout the samples. On the basis of d2σ/dε2 – ε plots, it was found that twinning occurs at almost all -T combinations examined in present study for 0Li and 1Li alloys. In high Li alloys, twinning activity was found to be insignificant at low ε , resulting in low twin density than low Li alloys. Twinning occurs at very early stages of deformation. In the low T and high ε regime, extensive twinning in high Li alloys is noted. In high T regime, presence of twins was not prominent due to the preferential occurrence of DRX at twin boundaries. Estimated values of Q in high Li alloys were found to be very low and correspond to lattice/grain boundary diffusion of Li in Mg, indicating that cross slip is no longer the rate controlling mechanism. Instead, unpinning of kinks from Li atoms appears to control the deformation. Cross slip is promoted by Li through increase in SFE at basal planes. Onset of the DRX was predicted and it was observed that high Li alloys posses lower σc at low ε , but at high ε , σc was either comparable to or higher than low Li alloys. Processing maps were generated for all the alloys using Prasad's as well as Murty's models. Instability predictions of Prasad’s and Murty’s models are similar, except that isoefficiency contours in the latter are slightly shifted to higher ε . These maps indicate to an increase in the workability with the addition of Li to AZ31. Instability predicted by processing maps in the low ε regime in high Li alloys is attributed to underestimation of stress values due to spline interpolation. High sensitivity observed for high Li alloy at intermediate ε (10-1 – 100 s-1) is attributed to the change in the deformation mode i.e. from slip to twinning. Deformation at high T leads to dissolution of Li containing precipitates, which in turn increases the solid solution strengthening in the alloy. Hence, increase in flow stress is observed with increase in T in high Li alloys. This structural change too causes instability predictions in the high -T regime. The 0 Li alloy exhibits peak efficiency of 45% in T = 250-400 °C and ε = 10-1.25 - 100.25 s-1 regime. DRX is observed in this regime and optimum conditions for deformation predicted for this alloys are T = 350 °C and ε = 10-1 s-1. These alloys can be worked at low ε regime too (T = 250-400 °C and ε = 10-2.5 – 10-1 s-1) where the softening mechanism is DRY. Accordingly, it is concluded that the intrinsic workability of AZ31Mg-alloy increases with the addition of 3% and 5% Li.

For ecological reasons, the current main challenge of the automotive industry is to reduce the fuel consumption of vehicles and then emissions of greenhouse gas. In this context, steelmakers and automotive manufacturers decided for some years now to join their efforts to promote the development and use of advanced high strength steels such as TRIP steels. A combination of high strength and large elongation is obtained thanks to the TRansformation Induced Plasticity (TRIP) effect. However, improvement of the mechanical properties is still possible, especially by the refinement of the matrix. In this work, two main ways were followed in order to reach improved properties. The classical way consisting of the annealing of cold-rolled samples and an innovative way consisting of obtaining the desired microstructure by direct hot rolling of the samples. In the classical way, this refinement can be obtained by acting on the chemical composition (with such alloying elements like Cu and Nb). It was observed that complete recrystallisation of the ferrite matrix is quite impossible in presence of Cu precipitates. In addition, if the ferrite recrystallisation is not completed before reaching the eutectoid temperature, the recrystallisation will be slowed down by a large way. An innovative heat treatment consisting in keeping the copper in solid solution in the high-Cu steel was developed. Therefore, ferrite recrystallises quite easily and very fine ferrite grains (~1µm) were obtained. In the innovative way, the effects of hot-rolling conditions on TRIP-assisted multiphase steels are of major importance for industrial practice and could open new dimensions for the TRIP steels (i.e. thanks to precipitation mechanisms leading to additive strengthening). Impressive mechanical properties (true stress at maximum load of 1500 MPa and true strain at uniform elongation of 0.22) were obtained with a relatively easy thermomechanical process, the role played by Nb being essential.

L’objectif de ma thèse consiste en l’étude de l’influence de l’orientation cristalline sur les microstructures de déformation et l’adoucissement (restauration, germination de la recristallisation) d’alliages Al-Mn.Les évolutions microstructurales de monocristaux d’orientation Laiton, Goss et S déformés en compression plane (0,15<ε<2,1) ont tout d’abord été caractérisées par la technique EBSD couplée à un MEB-FEG. Aux petites déformations, les microbandes s’alignent principalement sur les plans de cission maximale (indépendamment de l’orientation cristalline) ; alors qu’à des déformations plus importantes, elles s’alignent majoritairement sur les systèmes de glissement activés. Une structure lamellaire apparaît aux grandes déformations.Ensuite, les mécanismes de la restauration (à 240-320°C) dans ces mêmes monocristaux déformés (ε=2,1) ont été caractérisés par microdureté Vickers, par EBSD et par analyses des profils des pics de diffraction RX. La cinétique de restauration des monocristaux Laiton est systématiquement plus lente que celle des monocristaux Goss et S. L’influence de l’orientation serait alors attribuée aux faibles désorientations développées au cours de la déformation plastique pour les monocristaux Laiton (moyenne autour de 4°) comparativement à celles des monocristaux Goss et S (autour de 7-8°).Enfin, nous avons étudié l’adoucissement dans un polycristal déformé par une corrélation directe de la microstructure avant et après recuit. Deux principaux types de fragments Cube ont été mis en évidence dans l’état déformé. Seuls les fragments Cube « intergranulaires » permettent le développement rapide de grains Cube recristallisés. / The aim of my tesis was to evaluate the influence of crystalline orientation in deformation microstructures and softening (recovery, recrystallization) in cold-rolled Al-Mn alloys.The deformation microstructures of Al–Mn single crystals (namely Brass, Goss and S) have been characterized after channel-die compression up to true strains of 2.1 by EBSD in a FEG-SEM. There is a general tendency for the microbands to be non-crystallographic at low strains, then crystallographic, and finally mixed at high strains with some lamellar banding.The recovery behaviour (at 240-320°C) of the cold-rolled Al-0.1%Mn crystals (ε=2.1) was investigated by Vickers microhardness, EBSD and X-ray line broadening analysis. The microhardness recovery rates of the Brass oriented crystals are systematically lower than those of the Goss and S orientations. We thus suggest that the orientation dependency is ascribed to the relatively low misorientations developed by plastic straining in the Brass crystals (average about 4°) compared with the Goss and S orientations (about 7-8°).Finally, softening investigations in strongly deformed Al-0.1%Mn polycrystals were carried out to correlate the deformation microstructure with the cube recrystallization nucleation. Two major types of thin cube bands have been identified. Only the “intergranular” cube segments (usually between different S and Cu oriented grains) led to the formation of high growth rate recrystallized cube grains. The “transgranular” cube bands did not lead to a growth advantage for the cube components compared to components of the surrounding matrix.

L'objectif de ce travail est de prédire les évolutions microstructurales se produisant dans le tantale pur lors d'un traitement thermique en fonction de son état microstructural initial. La restauration, la recristallisation et la croissance de grains sont décrites à l'aide d'un modèle en champ moyen qui nécessite une description adéquate de la microstructure, en termes de distributions de tailles de grains et de densités de dislocations équivalentes. La densité de dislocation équivalente moyenne peut être évaluée par une simple mesure de dureté Vickers. L'établissement de la relation dureté-densité de dislocations nécessite l'utilisation d'une loi de comportement basée sur la densité de dislocations équivalente. Les évolutions microstructurales au cours d'un traitement thermique ont été observées et les paramètres pilotant ces phénomènes ont été identifiés à l'aide d'essais originaux comme l'observation in situ de la recristallisation ou l'utilisation d'essais à gradient de déformation pour déterminer le seuil de densité de dislocations équivalente pour déclencher la recristallisation. Des essais plus classiques ont permis d'obtenir des cinétiques de recristallisation dans la gamme 1000°C-1100°C pour différentes microstructures initiales. Les simulations des différents traitements thermiques à l'aide du modèle à champ moyen rendent bien compte des évolutions microstructurales en termes de fraction recristallisée et de taille des grains recristallisés pour des microstructures faiblement déformées ou fortement déformées et fragmentées, en utilisant une description adéquate du type de microstructure initiale. Le modèle devra en revanche être adapté pour traiter le cas de microstructures intermédiaires, en enrichissant non seulement la description de la microstructure initiale mais également celle de l'étape de germination des grains recristallisés. Il deviendra alors capable de prédire les évolutions de microstructures pour tout type de microstructure initiale de tantale. / This study aims at predicting the microstructural evolution of pure tantalum during annealing according the initial microstructural state. Static recovery and discontinuous recrystallization as well as grain growth are described using a mean-field model requiring an appropriate description of the microstructure, using both equivalent dislocation densities and grain sizes distributions. The average equivalent dislocation density can be assessed from Vickers microhardness measurements. The calibration of such a relation between microhardness and dislocation density involves the use of a dislocation density-based constitutive law. Microstructural evolutions during annealing have been observed and control parameters of these phenomena have been determined using original tests such as in situ observation of the recrystallization process or the use of strain gradient samples to assess the critical dislocation density for the onset of recrystallization. More classical tests have been carried out to get recrystallization kinetics in the range 1000-1100°C for different initial microstructures. Simulations of annealing using the mean-field model adapted for tantalum match the experimental evolution of both recrystallized fraction and recrystallized grain size, in either weakly deformed or severely deformed and fragmented microstructures. On the other hand, the model needs to be further adapted for intermediate microstructures, with both a more elaborate description of the initial microstructure and of the nucleation stage of the recrystallized grains. It will then be suitable to predict evolutions of any initial tantalum microstructure during annealing.

Au cours de leur mise en forme, les alliages de titane destinés à la fabrication de pièces tournantes pour moteurs d'avions suivent un schéma thermomécanique complexe constitué généralement de plusieurs opérations de forgeage. L'étape de forgeage dans le domaine monophasé β joue un rôle important, car elle conditionne la transformation de phases qui s'opère au cours du refroidissement ou du traitement thermique consécutif dans le domaine biphasé α-β, et donc les propriétés mécaniques finales de la pièce. La maîtrise de l'évolution de la microstructure et de la texture cristallographique au cours du forgeage dans le domaine β est donc indispensable pour optimiser l'ensemble du procédé de mise en forme. Pour cela, il est important de bien comprendre les mécanismes de recristallisation dynamique (continue et géométrique) se produisant dans ce type de matériau.Dans cette étude, les effets de la température, de la déformation et de la vitesse de déformation ont été étudiés au moyen d'essais de compression uniaxiale et de torsion à chaud. Les microstructures et textures de déformation ont été caractérisées par diffraction des électrons rétrodiffusés (EBSD). Ces approches expérimentales sont associées à un travail de modélisation, pour lequel le schéma de recristallisation dynamique "continue" (ou CDRX), consistant en une fragmentation progressive des grains β initiaux par la formation de nouveaux joints de grains, a été adapté à partir d'études antérieures. Les paramètres caractérisant les mécanismes élémentaires de la CDRX (écrouissage, restauration dynamique, migration des joints) ont été déterminés par ajustement sur les données expérimentales.Ces travaux ont pour objectif l'élaboration d'un post-processeur métallurgique dédié au forgeage des alliages de titane en phase β. / Titanium alloys used for the manufacture of rotating parts of aircraft engines undergo complex thermomechanical processing schedules, involving usually several forging operations. The forging step in the single -phase domain plays an important role, because it governs the phase transformation that occurs during cooling or subsequent heat treatment in the two-phase α+β range, and therefore the final mechanical properties of the workpiece. Controlling the microstructural evolutions during forging in the β-domain is of prime interest to optimize the entire process of disks manufacture. A full understanding of the (continuous and geometric) dynamic recrystallization mechanisms occurring in this type of material is therefore required.In this study, the effects of temperature, strain and strain rate were investigated by hot uniaxial compression and torsion tests. The microstructures and textures were characterized using backscattering electron diffraction (EBSD). These experimental approaches were associated with the development of a physical model. In the latter, the mechanism of "continuous" dynamic recrystallization (CDRX), consisting of a progressive initial fragmentation of the grains leading to the formation of new grain boundaries, was adapted from former studies. The parameters characterizing the elementary mechanisms of CDRX (strain hardening, dynamic recovery, grain boundary migration) were determined by fitting the experimental data.The final objective of this work is to develop a metallurgical post-processor dedicated to forging operations of titanium alloys in the -phase range.

Les propriétés des matériaux métalliques sont très liées à leurs caractéristiques microstructurales. Par exemple il est bien connu que la taille de grains joue sur la limite élastique du matériau ainsi que sur ses capacités d'écrouissage. Ainsi, la compréhension et la modélisation de l'évolution de la microstructure d'un métal pendant un traitement thermomécanique est d'une importance primordiale afin de prédire finement son comportement ainsi que ses propriétés finales. Dans le cadre de cette thèse, nous nous sommes concentrés sur la modélisation, à l'échelle d'un agrégat polycristallin, de la plasticité cristalline, de la recristallisation statique et de la croissance des grains dans un contexte de mobilité et d'énergie d'interface isotrope. Un modèle à champ complet dans un cadre éléments finis (EF) est proposé. Les grains sont représentés grâce à un formalisme level-set. L'étude EF développée peut être divisée en trois grandes parties: la génération statistique de microstructures digitales, la modélisation de la plasticité cristalline et la modélisation de la migration des joins de grains en régime de recristallisation statique. Concernant la génération statistique des microstructures digitales, une étude comparative entre deux méthodes de génération (Voronoï et Laguerre-Voronoï) a été réalisée. La capacité de la deuxième approche à respecter une microstructure basée sur des données expérimentales est mise en valeur en 2D et en 3D. Dans une deuxième étape, la plasticité cristalline des matériaux métalliques est étudiée. Deux modèles d'écrouissage ont été implémentés et validés : un premier modèle considérant uniquement les densités de dislocations totales, et un deuxième modèle différenciant les dislocations statistiquement stockées (SSDs) des dislocations géométriquement nécessaires (GNDs). Afin de valider l'implémentation de ces deux modèles issus de la littérature deux cas ont été étudiés : le premier correspond à l'étude à chaud d'un essai de compression plane d'un acier 304L, et le deuxième correspond à l'étude d'un essai à froid de compression simple d'un oligocristal de tantale composé de 6 grains. Les résultats numériques obtenus sont comparés avec les données expérimentales des deux essais. La migration des joints de grains est étudiée dans le contexte des régimes de recristallisation statique et de croissance de grains. Par rapport aux travaux pre-existants dans un cadre level-set, l'accent est mis sur la prise en compte des forces capillaires. La croissance des grains pure est en effet développée dans le formalisme éléments finis/level set considéré, et des validations à partir de résultats analytiques connus sont présentées. De plus, un travail d'analyse de modèles de croissance des grains à champ moyen existant dans la littérature est réalisé. Deux modèles en particuliers sont étudiés : celui de Burke et Turnbull et celui de Hillert/Abbruzzese. En comparant ces modèles avec les résultats obtenus par l'approche en champ complet développée, il est mis en évidence que le modèle simple de Burke et Turnbull n'est pas approprié pour décrire la croissance de grains pour tout type de distribution initiale de taille de grains. La recristallisation statique est ensuite abordée, avec une prise en compte des deux forces motrices liées (i) aux gradients d'énergies stockées sous la forme de dislocations, et (ii) aux effets capillaires. L'influence des effets de capillarité apparaît comme fortement liée à la distribution spatiale des nouveaux germes. Finalement, les résultats des simulations réalisées en plasticité cristalline sont utilisés comme données d'entrée du modèle de recristallisation statique développé. La comparaison des prédictions obtenues comparativement aux résultats expérimentaux sur 304L permet d'illustrer la pertinence d'une approche de type SSD/GND afin de prédire les sites de germination potentiels. / Mechanical and functional properties of metals are strongly related to their microstructures, which are themselves inherited from thermal and mechanical processing. For example, the material grain size distribution plays an important role on the material yield limit and work hardening. The understanding of these microstructure evolutions during thermo-mechanical processes is of prime importance for a better prediction and control of the material mechanical properties. During this Ph.D., we have worked on the modelling of crystal plasticity, static recrystallization and grain growth at the mesoscopic scale in the context of isotropic mobility and interface energy. The full field model developed is based on a finite element formulation combined with a level set framework used to describe the granular structure. This Ph.D. thesis is divided in three main parts: statistical generation of digital microstructures, crystal plasticity modelling and grain boundary migration modelling. In what concerns the digital microstructures statistical generation, a comparative study between two methods (Voronoï and Laguerre-Voronoï) is presented. The ability of the second approach to respect a given grain size distribution is highlighted in 2D and 3D. Secondly, the metallic materials crystal plasticity is studied. Two hardening laws have been implemented and validated: the first one considering the total dislocation density and a second one that differentiates the statistically stored dislocations (SSD) from geometrically necessary dislocations (GNDs). Two different tests cases are used in order to validate the implementation of both hardening laws in the considered crystal plasticity model. The first one corresponds to a planar hot compression test (channel die test) on a 304L stainless steel whereas the second one corresponds to a simple cold compression test on a tantalum olygocrystal composed by six different grains. The obtained results are compared to experimental data for both cases. Grain boundary migration is studied for static recrystallization and grain growth phenomena. Compared to previous work in the considered level-set framework, the focus is on the consideration of capillary forces. Indeed pure grain growth is developed in the considered finite elements/level set formalism and this algorithm is validated using well-known analytical results. Moreover, the results of the developed full field grain growth model are compared in 2D with several well-known mean field grain growth models (Burke and Turbull model and Hillert/Abbruzzese model). The results obtained illustrate that only the Hillert/Abbruzzese model accurately describes grain growth kinetics for all initial grain size distributions. The validity of the Burke and Turnbull model is, on the contrary, restricted to specific distributions. Static recrystallization is then discussed considering both driving forces: (i) internal energy gradient and (ii) grain boundaries capillarity effects. The influence of capillary effects appears to be strongly related to the spatial distribution of the new grains. Finally, the crystal plasticity numerical results are used as input data of the developed static recrystallization full field model. The comparison of the numerical predictions obtained with 304L experimental results allows illustrating the relevance of the SSDs/GNDs formalism used concerning the prediction of the nuclei potential position.