Aluminium alloys, which are the most widely used materials in the aircraft and aerospace industries, find their applications due to high strength–to-density ratio, resistance to catastrophic fracture, high degree of toughness, fabricability including good weldability and availability. High strength aluminum alloys are used in different forms like sheets, forgings and extruded rods, welded and machined components in the aerospace industry. One major application of the aluminium alloys in the space sector is in the launch vehicle and satellite sub-systems. The Indian Space Research Organization has met major challenges of indigenization of suitable aluminium alloys, for example, Al-Cu alloys (like AA2219) and Al–Zn-Mg alloys (like AA7075 and AFNOR 7020). Many failures of the metallic sub-systems made of different grades of aluminum alloys have confirmed that high levels of residual stresses and unacceptable microstructures have played a role. Crystallographic texture in these materials has a very significant role to play in the performance of these materials in service. The anisotropy in the mechanical properties caused by crystallographic texture would add to the woes of the existing problems of residual stresses and directionality in the microstructure. In this context, a detailed study of crystallographic texture and residual stresses of high strength aluminium alloys is mandatory. It is also important to study the influence of texture on the anisotropy in mechanical properties. The present research programme aims at addressing some of these aspects. The entire work has been divided in three major sections, namely macro and micro texture analysis, non-destructive measurement of residual stresses using X-ray Diffraction (XRD) and the Ultrasonic Testing (UST) and the study of anisotropy in the mechanical properties arising due to the above two factors. The thesis composition is as follows. In Chapter I, a detailed survey of the literature has been presented wherein basic physical metallurgy for different aluminum alloys of interest has been given. Thereafter, details of texture measurement by the X-ray diffraction and Electron Back Scatter Diffraction (EBSD) are presented. This is followed by a detailed review on the texture studies carried out in aluminium alloys under various conditions. Literature review on the two non-destructive methods, namely the X-ray diffraction and ultrasonic method has been carried out in detail. In order to account for microstructural changes, Differential Scanning Calorimetry (DSC) was carried out. Recent work on the mechanical property anisotropy arising due to high degree of mechanical working in aluminium alloys has been reviewed. Chapter II includes the experimental details involved in the course of the present investigation. The procedural details of cold rolling and associated microstructural changes are given in this chapter. This is followed by the texture measurement methods. Experimental details of the bulk texture measurement using the X-ray diffraction and micro texture measurements by the Electron Back Scatter Diffraction (EBSD) in the SEM are described. Details of the texture computation procedure as well as micro texture analysis methods are also presented. Basic principles of the non-destructive methods of measuring residual stresses, viz., the X-ray diffraction and the Ultrasonic testing, including the theory of measurements, are dealt with. Finally, the details of measurements of anisotropy in mechanical properties, including simulation carried out, for the three alloys are delineated. Chapter III deals with the results of the crystallographic texture measurements carried out on the cold rolled and artificially aged aluminium alloys. Results obtained from the pole figure analysis, Orientation Distribution Function (ODF) method and estimation of the various fibres present in the cold rolled material and the volume fraction of the texture components are discussed in detail for the three aluminium alloys. Results of the micro texture measurements using the EBSD are presented, explained and analyzed in detail. A comparison of the inverse pole figures (IPFs), Image Quality (IQ) maps, Misorientation angle, Grain Orientation Spread (GOS), Kernal Average Misorientation (KAM), CSL boundaries, Grain size and Grain boundary character distribution (GBCD) for materials cold rolled to different reduction for each of the alloys are done and analyzed. Conclusions are drawn regarding the evolution of texture from the above analysis. Deformation texture components Cu, Bs and S increase from the starting material as the rolling percentage increases. On the other hand, recrystallization texture components of Goss and Cube are observed to be weak. AFNOR 7020 developed the strongest texture followed by the AA7075 and AA2219 alloys. The Bs component is stronger in AFNOR 7020 alloy. This is attributed to the shear banding. Average KAM value increases as the cold working in the material increases confirming that the material contains high dislocation density at higher working percentages. Chapter IV deals with residual stresses in the aluminium alloys. Measurement of residual stresses has been carried out on the same sheets and plates, wherever it was possible, using the two methods. The residual stresses have been measured in two mutually perpendicular directions of the aluminium alloy sheets. Residual stress measurements by the ultrasonic method using the Critically Refracted Longitudinal (LCR) wave technique is also used to measure the subsurface stresses non-destructively. Acousto Elastic Coefficients (AEC) is determined for the alloys, in uniaxial tension. Using the AEC for the alloys, the RS at a depth of 3mm are evaluated using a 2MHz probe. Results of the stresses measured by the two methods have been discussed. The trends and anisotropy in the stress values due to texture are discussed and compared with the literature available. Surface residual stresses by the XRD method show compressive stresses at a majority of the locations. Residual stresses measured by the ultrasonic technique, which has a depth of penetration of about 3mm, have shown tensile stresses on many locations. Residual stresses are influenced by the crystallographic texture. Anisotropy in stress values in the longitudinal and transverse directions is demonstrated. In Chapter V, the anisotropy in mechanical properties for the three alloys is discussed in detail. The anisotropy in the three directions, namely the parallel, transverse and 45 deg orientation to the rolling directions is evaluated. The Lankford parameter, otherwise known as Plastic Anisotropy Ratio “r”, has been measured from the tensile tests of the alloy samples in the cold rolled conditions. These have been compared with the computed “r” from the XRD ODF data using the VPSC simulations and found to be qualitatively matching. These trends are discussed with the available literature on the anisotropy of the mechanical properties for aluminium alloys. Samples subjected to high cold rolling show anisotropy of UTS, YS and ‘n’ values. Experimentally measured “r” values in all the deformation conditions match the trend qualitatively with the simulated ones. The maximum anisotropy was observed at 45o orientation to the rolling direction in all the three alloys. Chapter VI gives the summary of the results from the study and the suggestions for future work.

Le contexte environnemental (réchauffement climatique) et économique (épuisement des ressources en énergies fossiles) entraîne une nécessaire mutation du paysage énergétique mondial. L’hydrogène est présenté comme un vecteur d’énergie propre pouvant, par l’intermédiaire d’une pile à combustible, fournir de l’électricité pour diverses applications (nomade, portable, automobile et stationnaire). Cependant, son développement reste tributaire de son mode de stockage. Parmi les composés présentant de bonnes capacités de stockage, le borohydrure de sodium NaBH4 se distingue puisqu’il permet aussi un dégagement contrôlé de l’hydrogène d’après la réaction d’hydrolyse suivante : ( ) (2 ) ( ) ( ) 4 ( ) 4 2 2 2 2 NaBH ++ x H O l→NaBO . xH O + H g Il constitue ainsi une solution sûre et facile d’utilisation, et est donc envisageable pour des applications grand public. La thèse avait pour objectif l’approfondissement des connaissances relatives à la réaction catalysée d’hydrolyse du borohydrure de sodium selon deux axes principaux: la catalyse de la réaction et l’étude des produits d’hydrolyse. Concernant le premier axe, notre objectif était de mieux comprendre et d’améliorer la cinétique de la réaction d’hydrolyse, les catalyseurs étudiés étant à base de cobalt. Un catalyseur « modèle » a été utilisé et comparé à des nanoparticules métalliques synthétisées et d’autres espèces chimiques à base de cobalt (oxyde, hydroxyle et carbonate). Le modèle cinétique de Langmuir-Hinshelwood a permis de décrire la cinétique de l’hydrolyse. Un mécanisme réactionnel basé sur les adsorptions en surface du catalyseur de BH4 - et de H2O a été proposé. Enfin, la nature des sites actifs en surface a été discutée. En ce qui concerne le second axe de la thèse, nous avions deux objectifs : identifier les phases formées en fonction des conditions expérimentales et approfondir les connaissances thermodynamiques du système binaire NaBO2-H2O pour définir les différents équilibres se formant à l’issu de la réaction d’hydrolyse. Pour ce faire, les borates ont d’abord été synthétisés, puis caractérisés en termes de structure cristallographique et de stabilité en température. C’est ainsi qu’un nouveau borate de sodium, Na3[B3O4(OH)4] ou NaBO2•2/3H2O, a été obtenu. D’autre part, l’étude des équilibres liquide+solide, solide+solide et liquide+vapeur nous a permis d’établir le diagramme binaire NaBO2-H2O à pression atmosphérique. / As an alternative solution to fossil fuels, hydrogen is may be the most advanced technology. However, its large scale development is today harshly hindered by the issues it encounters, its storage being certainly the most significant. Various storage methods are under investigation but solid storage as in sodium borohydride NaBH4 appears to be convenient with regard to its storage capacities, safety and cost. The hydrogen stored in NaBH4 can be released by hydrolysis at ambient temperature. The hydrolysis reaction leads to the formation of 4 hydrogen molecules and borates: ( ) (2 ) ( ) ( ) 4 ( ) 4 2 2 2 2 NaBH ++ x H O l → NaBO . xH O + H gThe efficiency of this reaction suffers from two problems. First, slow kinetics of hydrogen release is observed for this reaction. Second, the “hydration” of NaBO2 is detrimental to the storage capacities of the system NaBH4-H2O. Indeed, the higher the pseudo-hydration degree (i.e. x), the lower the gravimetric hydrogen storage capacity. Both issues are the topics we have studied in the present work. Hydrogen release can be accelerated by using a cobalt catalyst. Hence, we focused on various cobalt-based catalysts. A reference catalyst was first chosen, and then tested and compared to lab-prepared cobalt nanoparticles and other cobalt-based materials (oxide, hydroxide and carbonate). The Langmuir-Hinshelwood kinetic model well captured the kinetics of the hydrolysis reaction. Accordingly, a reaction mechanism based on the adsorptions of both BH4 - and H2O on the catalyst surface has been proposed. The adsorptions are expected to occur on specific surface sites which nature has been discussed. The gravimetric hydrogen storage capacity of NaBH4-H2O can be increased by decreasing the pseudo-hydration degree (i.e. x) of the borates. However, this implies that the thermodynamics of the NaBO2•xH2O compounds are well known as they are crucial for favouring the formation of water-free borates. Borates were then synthesized and characterized in terms of crystallographic structure, pseudo-hydration degree and thermal stability. In this context, a new sodium borate has been synthesized: Na3[B3O4(OH)4] or NaBO2•2/3H2O. Besides, we studied the liquid+solid, liquid+vapor and solid+solid equilibria that permitted to set the binary phase diagram NaBO2-H2O at atmospheric pressure