The effect of friction stir welding on the microstructure, precipitation, mechanical properties, and tensile fracture has been studied. Friction stir welding has been applied to a third generation Al-Cu-Li alloy, the AA2199, in the T3 condition. Post weld heat treatment (PWHT) to the T8 condition, was carried out to artificially age the welds and improve mechanical properties. Welds were characterised using field emission scanning electron microscopy (FE-SEM) with electron channeling contrast imaging (ECCI), differential scanning calorimetry (DSC), micro-hardness, and tensile testing. Welds created with tool rotation speed of 877RPM showed ultimate tensile strength level of 93% of base metal in the T8, an elongation of 6% at fracture, and microhardness values ranging between 120-140 HV across the welds. The ability of welds to gain in hardness and strength during PWHT has been linked to the limited formation of large scale precipitates which act as sinks for alloying elements. / L'effet du soudage par friction-malaxage sur la microstructure, la precipitation, les propriétés mécaniques et la rupture par traction ont été étudiés. Le soudage par friction-malaxage a été appliqué à une troisième génération d'alliage d'Al-Cu-Li, le AA2199-T3. Un traitement thermique après soudage (PWHT) sur l'alliage AA2199-T8 a été réalisé pour vieillir les soudures artificiellement et en améliorer les propriétés mécaniques. Les soudures ont été caractérisées par microscopie électronique à balayage (FE-SEM), par imagerie en contraste cristallographique (ECCI), par calorimétrie différentielle à balayage (DSC) et par des essais de micro-dureté et de traction. Les soudures créées avec une vitesse de rotation d'outil de 877RPM ont montré une limite à la rupture de 93% par rapport la plaque de depart, un allongement à la rupture de 6% , et des valeurs de microdureté variant entre 120 à 140 HV dans les soudures. Le gain en dureté et en résistance du matériau dans les zones soudées au cours du traitement thermique PWHT est lié à la formation à grande échelle de précipités absorbant les éléments d'alliage.

Among various natural biopolymers, type I collagen gels have demonstrated the highest potential as biomimetic scaffolds for tissue engineering (TE). However, the successful application of collagen gels requires a greater understanding of the relationship between their microstructure and physical-mechanical properties. Therefore, a precise method to modulate collagen gel microstructure in order to attain optimal scaffold properties for diverse biomedical applications is necessary. This dissertation describes a new approach to produce collagen gels with defined microstructures, quantified by hydraulic permeability ( k), in order to optimize scaffold properties for TE applications. It was hypothesized that the measurement of k can be used to study the role of microstructure in collagen gel properties, as well as cell function and cell-scaffold interactions. Applying increasing levels of plastic compression (PC) to the highly hydrated collagen gels resulted in an increase in collagen fibrillar density, reduced Happel model derived k values, increased gel stiffness, promoted MSC metabolic activity, osteogenic differentiation, and mineral deposition, while cell-induced gel contraction diminished. Thus, collagen gels with lower k and higher stiffness values exhibited greater potential for bone tissue engineering. / Correlating between collagen gel microstructure, k, and fibroblast function within collagen gels indicated that increasing the level of PC yielded a reduction in pore size and an increase in fibril bundle diameter. Decrease in k values resulted in a decrease in gel contraction and an increase in cell metabolic activity. An increase in cell density accelerated contraction. Therefore, fibroblast function within collagen gels can be optimised by a balance between the microstructure, k, and cell seeding density. / Developing a micromechanical model to measure experimental k of collagen gels during confined compression revealed the formation of a dense collagen lamella at the fluid expulsion boundary, thereby generating a two-layer model. By applying gel mass loss into Darcy's law, experimental k values of the lamella, along with the thickness of lamella (c) and hydrated gel layer (b) were measured. An increase in either compression level or compression time resulted in a decrease in k, decrease in b, and an increase in c. In conclusion, controlled compression of collagen gels can be used to produce multi-layered biomimetic scaffolds with defined microstructures and k in order to attain optimal properties for tissue engineering applications.

The principles governing pattern formation in discotic nematic liquid crystalline fibers subjected to uniaxial extensional flows are established. Computational and analytical methods are used in conjunction with bifurcational techniques to simulate the structural characteristics of the orientational patterns that arise by stretching discotic nematic liquid crystalline materials. The analytical and numerical results are in excellent agreement with actual cross-sectional fiber textures obtained by melt spinning carbonaceous mesophases. This work reproduces the main structural features of the oscillatory zig-zag pattern commonly observed in mesophase carbon fibers, and identifies the process conditions that lead to this peculiar fiber texture. In addition, the temperature driven texture transitions and the emergence of random pattern also observed during the industrial manufacturing of mesophase carbon fibers are captured by the simulations and thoroughly explained using classical viscoelastic theories of liquid crystalline materials.

Aluminum nitride ceramics are in high demand for applications involving substrate materials for high speed, high capacity, and complex integrated circuits requiring high thermal conductivity. Hot pressing and liquid-phase sintering are the most common processing techniques used to fabricate AlN ceramics. Liquid-phase sintering involves the use of additives to enhance the sinterability, and in the case of AlN, the thermal conductivity. The function of the additives is to react with an oxide layer on the powder surface and form a liquid phase. The presence of this liquid phase aids densification and the removal of oxygen from the AlN lattice, the latter results in significant thermal conductivity enhancement. / Liquid-phase sintering of AlN with $ rm Y sb2O sb3$ as an additive has been studied to control the formation of the secondary phases. Using the $ rm Y sb2O sb3$-$ rm Al sb2O sb3$ phase equilibria, three liquid-phase sintering compositions occurring at the eutectic points and one composition close to that of $ rm3Y sb2O sb3 5Al sb2O sb3$ (Yttrium Aluminum Garnet, YAG) were chosen. Sintering was performed in the temperature range of 1750-1950$ sp circ$C for 1 hour under a N$ sb2$ atmosphere to optimize the sintering temperature for each composition. Full densification of the AlN was achieved for all four compositions sintered at 1900$ sp circ$C. / Investigation of the sintering kinetics was performed in a AlN/BN powder bed and on a BN setter at 1900$ sp circ$C for up to 4 hours. The kinetic study results did not agree with the classical and recently proposed liquid-phase sintering models due to the different mechanisms of liquid phase formation, and a difference in the chemical composition and viscosity of the various secondary phases. / The microstructural evolution of sintered AlN was studied by SEM and TEM. The thermal conductivity of the fully sintered materials was measured, and the highest value achieved was 148.5 W/mK from the YAG composition due to the absence of the secondary phase film at grain junctions and the superior lattice oxygen absorption of the secondary phase compound to the other compositions. / A study of the post-sintering heat-treatment of AlN in various reducing atmospheres was performed to determine the influence on thermal conductivity. Two different schematic models of the reducing reactions were proposed. The results indicate that such a heat-treatment can improve the thermal conductivity of AlN up to nearly 200 W/mK. This is due to further oxygen removal from both the AlN lattice and secondary phase, simultaneously.

An electrochemical method of fabrication of (NiCoCrAlY)/MgO/Yttria stabilized zirconia (YSZ) multilayered coating was proposed. This multilayered coat is expected to work as a thermal barrier coating (TBC) for nickel superalloy substrates. The (NiCoCrAlY) layer was deposited using the electrophoretic deposition technique, the MgO layer was deposited by the electrolytic deposition technique and the YSZ layer was electrophoretically deposited. / In order to study the deposit morphology and to determine the appropriate processing parameters for the multilayered coat, one-layer coatings of (NiCoCrAlY), MgO and YSZ were deposited and characterized. At first, the process of depositing (NiCoCrAlY) alloy particles using an aqueous media with AlCl3 or Al(NO3)3 as an electrolyte revealed that the alloy particles were deposited at the same time as aluminium oxide. The co-deposited aluminium oxide worked as a binder between the particles and the substrate. / In the electrolytic deposition process of the MgO coating, the layer deposited from Mg(NO3)2 solution was mainly magnesium hydroxide and it had to be calcinated to form a MgO coating. An optimization of the deposition process demonstrated that a crack free deposit of MgO could be obtained at low current density. / An optimum condition of the electrophoretic deposition process was established for YSZ; it was found that adding 5% water to the acetone bath increased the deposition rate of the YSZ particles, and had increased the porosity in the coat. / A composite coating of (NiCoCrAlY)/MgO was formed after heat treatment at 850°C for 1 hr. The electrochemically deposited MgO was easily sintered at 850°C, which resulted in a dense ceramic coating that protects the substrate and the (NiCoCrAlY) coating from oxidation during sintering of the electrophoretically deposited YSZ layer at 1100°C.

Magnetic carrier technology (MCT) has found a wide range of applications, including biological cell separation, waste remediation, and raw material recovery. The challenge to MCT is to develop a new method for the preparation of magnetic carriers with the following features: high density of reactive functional groups, diversity of functionalities, and durability of surface films. In this thesis, two novel methods, molecular self-assembly and silanation, were developed for the preparation of magnetic carriers. / In molecular self-assembly, 16-mercaptohexadecanoic acid (HOOC-$ rm C sb{15}H sb{30}$-SH, ie. MHA) was anchored onto the $ gamma$-Fe$ rm sb2O sb3$ surface through chemical bonding between the carboxylic head group of the surfactant and iron on the surface, leaving the thiol or disulfide groups reactive. The molecular orientation of MHA self-assembled on $ gamma$-Fe$ rm sb2O sb3$ was studied by x-ray photoelectron spectroscopy (XPS), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and film flotation. The self-assembled MHA film on $ gamma$-$ rm Fe sb2O sb3$ was immobilized and resistant to acid and base attack. Magnetic carriers prepared as such showed a strong affinity to Ag$ sp+$ and Cu$ sp{2+}$ ions in an aqueous solution. / In the preparation of magnetic carriers by silanation using 3-amino-propyltriethoxy silane (APTES), XPS, DRIFTS, and zeta-potential measurements indicated that direct silanation of APTES from either water or toluene solutions on bare magnetic particles was successful. In acid solutions, APTES films silanized on bare magnetic particles from toluene were more stable compared to the ones silanized from water. Both films were unstable in alkaline solutions. To improve the stability of silanized films, a thin silica layer was coated onto the magnetic particles using the sol-gel process, followed by dense liquid silica coating. Magnetic carriers with amino groups were prepared by the silanation of silica coated magnetic particles using APTES in toluene. Stability tests indicated that the silanized films on silica coated magnetic particles were more stable than the ones silanized on bare magnetic particles. / Magnetic carriers with reactive amine groups were proved to be effective for removal or recovery of heavy metal ions such as Cu$ sp{2+}$ and Zn$ sp{2+}$ from aqueous solutions. Loaded metal ions on magnetic carriers were completely stripped off by 0.01 M nitric or hydrochloric acid. The possible recycling of magnetic carriers could offset the high price of magnetic carriers and lower the cost associated with industrial applications. Applications of magnetic carriers with reactive amine and thiol groups in biological cell separation, immobilization of enzymes, magnetic fluids, and waste remediation were also discussed.

Copper has been recently used as an interconnecting material since it has high conductivity and good electromigration failure resistance. Recent studies show the close relationship between texture and reliability of Cu damascene interconnects. However, textural and microstructural evolutions of Cu damascene interconnects as function of substrate texture, current density, line width and annealing process are still not well understood. / At first, to understand the influence of substrate texture and electroplating conditions on the texture and surface morphology of Cu electrodeposits, three different polycrystalline copper specimens were used as substrates and electrodeposits were plated using different current densities. The mechanism of growth of Cu electrodeposits and the importance of smooth surface morphology were discussed. / To analyze the effect of line width and annealing process on textural and microstructural evolution of Cu damascene interconnects, Cu interconnects samples which have a different line width and different annealing process were investigated. According to x-ray diffraction (XRD) and electron backscattered diffraction (EBSD) results, the directional changes of (111) plane orientation with the different line width and annealing were observed. In addition, the analysis of microstructure and grain boundary character distribution (GBCD) of Cu damascene interconnects demonstrated that bamboo-like microstructure was developed in the narrow line and a polygranular structure was developed in the wider line. Also, the fraction of Sigma3 boundaries was changed depending on the line width and annealing process. / To analyze a relationship between the stress distribution and textural and microstructural evolution in the samples investigated, stress was calculated using finite element method (FEM), and these results were verified by physical stress simulation of copper in the Chapter 7. Through this investigation, it was found that the inhomogeneity of stress distribution in Cu damascene interconnects is an important factor which is necessary for understanding textural transformation after annealing, and the effects of stress on textural and microstructural evolution of Cu depends on the crystallographic texture and the annealing temperature. / A new interpretation of textural and microstructural evolution in Cu damascene interconnects lines after annealing and possible factors responsible for the texture transformation are suggested, and the optimum processing conditions are recommended.

In recent years, much development has been made in the world of nanotechnologies. Hence, nanomaterials, which possess unique characteristics and excellent mechanical properties, are now being used in innovative and advanced applications. Despite the incredible potential of nanomaterials, their use is still at an embryonic stage as a result of the difficulty to mass-produce them. Among the potentially viable application remains the fabrication of nanostructured powders to produce high temperature oxidation resistance coatings. / Nanostructured coatings were obtained by thermally spraying cryomilled CoNiCrAlY and NiCoCrAlY feedstock using the HVOF technique. It was found that the milling process used to prepare the powder significantly altered the microstructure of the alloy. In addition to achieving grain size refinement, significant aluminum segregation at grain boundaries was observed. Upon oxidation experiments up to 96 hours in static air at 1000°C an oxide scale composed of an adherent and dense α-Al2O3 inner layer with a top layer of fast growing oxides such as NiO, Cr2O3, CoAl2O4 and NiAl2O4 evolved from the coatings. It was found that the formation of a two-layer scale could be prevented through surface grinding prior to oxidation. Moreover, the comparison of the oxidation results of the powders and those of the coatings revealed that the spraying process has a considerable influence on the oxidation behavior of MCrAlYs attributable to the formation of oxide seeds during the spraying process. / Au cours des dernières années, plusieurs avancements ont vu le jour au niveau des nanotechnologies. L'émergence des métaux nanostructurés, possédant des charactéristiques inédites ainsi que des propriétés méchaniques amplement supérieures à celles des métaux conventionnels, a contribuée à leur utilisation pour de nouvelles applications. Malgré le potentiel immense de la nanotechnologie dans le monde des matériaux, l'utilisation de ces maérieux est encore limitée dû à la difficulté de les produire à grande échelle. Cependant, l'une de ces utilisations prometteuses consiste en le développement de poudre nanostructurée destinée à la production de revêtements résistant à l'oxidation à haute temperature. / Le comportement de revêtements nanostructués obtenus par projection thermique à partir de poudres de CoNiCrAlY et de NiCoCrAlY broyées cryogéniquement a été étudié dans un atmosphère oxidant. Il a été démontré que l'étape de broyage modifie considérablement la microstructure des poudres; en plus de réduire la taille de grain, le broyage a mené à une ségrégation de l'aluminum aux joints de grains. Cela a eu pour effet de favoriser la croissance d'une couche protectrice de α-Al2O3, bien adhérée et de bonne qualité lorsque les revêtemens ont été oxidés à une température de 1000°C pour des périodes allant jusqu'à 96 heures. Une seconde couche d'oxides à croissance rapide tels que NiO, Cr2O3, CoAl2O4 and NiAl2O4 a également été observée. Par contre, il a été démontré que cette dernière ne croît pas si la surface des revêtements est polie avant l'oxidation. De plus, en comparant les résultats des tests d'oxidation des poudres avec ceux des revêtements il a été démontré que la simple projection thermique des poudres influence les résultats d'oxidation due à la formation d'oxides durant la projection.

Cool deformation is a process in which a small amount of plastic deformation is applied at temperatures well below the end of the austenite transformation temperature. In this thesis, a systematic study was conducted to evaluate the microstructural evolution and mechanical properties of microalloyed steels processed by thermomechanical schedules incorporating cool deformation. Thermodynamic analysis was conducted to predict equilibrium phases formed by the presence of microalloying elements such as Ti, Nb, Mo and their appearance were then elaborated by means of TEM microscopy. As well, continuous cooling torsion (CCT) was employed to study the transformation behavior of steels for austenite conditioned and unconditioned. Cool deformation was incorporated into a full scale simulation of hot-rolling, and the effect of prior austenite conditioning on the cool deformability of microalloyed steels was investigated. Out of these studies, a new definition of no-recystallization temperature (Tnr) was proposed based on dynamic precipitation, which was then recognized in the Nb bearing steels by using TEM analysis as well as flow curves analysis. Results show that cool deformation greatly improves the strength of microalloyed steels. Of the several mechanisms identified, such as work hardening, precipitation, grain refinement, and strain induced transformation (SIT) of retained austenite, SIT was proposed, for the first time in microalloyed steels, to be the significant mechanism of strengthening due to the deformation in ferrite. Results also show that the effect of ferrite precipitation is greatly overshadowed by SIT at room temperature. Finally, considering the interplay of SIT and precipitation for the Nb bearing steels, a rolling schedule was designed incorporating austenite conditioning, cooling rate and cool deformation that maximized the strength. / La déformation à froid est un processus au cours duquel une petite déformation plastique est appliquée bien en dessous de la température finale de la transformation de l'austénite. Dans cette thèse, une étude systématique a été conduite afin d'évaluer l'évolution microstructurale des micro-alliages d'acier traités par des moyens thermomécaniques incluant la déformation à froid. L'analyse thermodynamique était menée afin de prédire des phases d'équilibre formées par les les éléments micro-alliants tels que le Ti, le Nb, le Mo. Leur apparence était expliquée par usage de la microscopie TEM. Parallèlement, la torsion de refroidissement continu (CCT) était aussi utilisée pour étudier le comportement dans la transformation des aciers pour les cas de l'austénite conditionné et non-conditionné. La déformation froide était insérée sur l'échelle complète de simulation du roulement à chaud et l'effet du conditionnement préalable de l'austénite sur la déformabilité des aciers micro-alliants, était étudié. Mises à part ces études, une nouvelle définition de la température de la non-recristallisation (Tnr) était proposée, basée sur la précipitation dynamique, laquelle était mise en évidence dans les aciers contenant du Nb, par usage de l'analyse par TEM et des courbes d'analyse des flux. Les résultats montrent que la déformation à froid améliore largement la résistance des aciers micro-alliés Parmi les divers mécanismes identifiés, tels que le durcissement, la précipitation, le raffinement du grain, et la transformation forcée (SIT) de l'austénite retenu, SIT était révélé pour la première fois comme étant un mécanisme important de durcissement dans le domaine des aciers micro-alliés, à cause de la transformation en ferrite. Les résultats montrent aussi que la précipitation de la ferrite est largement masquée par SIT à la température ambiante. Enfin, tenant compte des rôles joués par SIT et la précipitation dans le cas des aciers contenant du Nb, un programme de roulement a été conçu. Celui-ci comprend : le conditionnement de l'austénite, la vitesse de refroidissement, la déformation froide, laquelle maximise la résistance.

Microstructure and corrosion and tribo-corrosion behaviors of Ti-based and Si-based coatings have been systematically investigated. A series of Ti-based and Si-based coatings with different silicon and/or carbon contents were prepared by plasma enhanced chemical vapor deposition (PECVD). Various experimental techniques were employed for the microstructural characterization of the coatings, e.g., X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The mechanical and tribological properties were assessed using nano-indentation, micro-scratch test and pin-on-disk wear test. Corrosion resistance was measured using potentiodynamic polarization test and analyzed using electrochemical impedance spectroscopy (EIS), while the tribo-corrosion behavior was characterized using reciprocating wear test in corrosion environment in tribo-corrosion apparatus. The grain size refinement took place as the Si and C incorporated into the TiN coating. At the same time, the microstructure of the coatings changed and a transition from TiN columnar structure into densely packed homogeneous nano-composite structure was observed for nc-TiN/a-SiNx and nc-TiCN/a-SiCN coatings. This gave rise to a further improvement of the corrosion resistance by a factor of ~20 compared to TiN. Interface structure of the TiN coating system was designed in such a way that the hardness increased gradually with the distance from the substrate to the coating surface. This was done by applying a Cr interlayer in order to enhance the adhesion and simultaneously improve the load bearing capacity. In addition, the Cr interlayer further enhanced the corrosion resistance of the TiN-based nano-composite coatings. The Ti-Si-C coatings mainly consisted of nanocrystalline TiC particles embedded in the a-SiCx:H and a-C:H matrix. The refinement of the TiC grains and the increase of the amorphous fraction simultaneously took / La microstructure et le comportement en corrosion et en tribo-corrosion des revêtements à base de titane et de silicium ont été systématiquement étudiés. Une série de ces revêtements contenant différentes composition de silicium (Si) et/ou de carbone (C) ont été préparés par déposition chimique en phase vapeur assistée par plasma (PECVD). Différentes techniques expérimentales ont été utilisées pour la caractérisation de la microstructure des revêtements. Un raffinement de la taille des grains s'est produit lors de l'incorporation du Si ou du C dans la composition du revêtement TiN. Au même temps, la microstructure du revêtement a changé et une transition de la microstructure de colonnaire à celle nanocomposite, dense et homogène a été observée pour les revêtements nc-TiN/a-SiNx and nc-TiCN/a-SiCN. Cela a permit de rehausser la résistance à la corrosion d'un facteur de ~20 comparé au TiN. La structure de l'interface du système de revêtement TiN a été conçue de façon à ce que la dureté augmente graduellement avec la distance entre le substrat et la surface du revêtement. Cela a été réalisé en appliquant une couche intermédiaire de chrome (Cr) dans le but de rehausser l'adhésion et simultanément d'augmenter la capacité de chargement. En plus, la couche de Cr a permit l'augmentation de la résistance â la corrosion des revêtements nanocomposites à base de TiN. Les revêtements Ti-Si-C sont principalement constitués de particules nanocristallines de TiC incorporées dans une matrice amorphe a-SiCx:H and a-C:H. Le raffinement de la taille des grains de TiC et l'augmentation de la fraction de phase amorphe se produit lorsque plus de Si et/ou de C sont incorporés dans les revêtements Ti-Si-C. Cela a permit d'améliorer les propriétés électrochimiques du Ti-Si-C, lequel peut être attribué à la résistance à la corrosion supérieure et a la densité et l'homogénéité de la matrice -SiCx:H and a-C:H qui e