Ce travail de thèse propose d’interroger la place des loisirs de chasse, de pêche, de cueillette et d’observation naturaliste dans la préservation des espaces naturels de l’estuaire de la Seine. Le cadre conceptuel s’appuie sur la sociologie du loisir nord-américaine pour traiter ces activités selon la Perspective des Loisirs Sérieux. À travers une méthodologie qui mêle l’ethnographie, l’entretien récit de vie et le questionnaire, ces loisirs sont présentés comme le support de conflits mais aussi d’engagements, liés à l’étude, à la gestion et à la valorisation de la nature. L’analyse lie l’immersion dans l’environnement et la pratique de la prédation avec la construction de convictions écologiques d’ordre sociopolitique. La mise en cohérence de ces convictions est assurée par des passeurs qui font usage du loisir comme d’un outil de transaction sociale : il est un support de communication utilisé pour mettre en réseau les différents acteurs institutionnels et associatifs qui s’investissent dans la préservation de la nature. / This thesis proposes to question hunters, anglers, gatherers and wildlife watchers as part of the network which preserve the natural spaces around the river Seine estuary. The conceptual framework is based on North American sociology of leisure. These activities are considered according to the Serious Leisure Perspective. Through a methodology that combines ethnography, interviews and survey, these activities are described as support for volunteering.The analysis links the practice of predation with ecological convictions. Leisure is also used as a communication medium and help creating a consistent network to preserve nature.

In the presented thesis, lead-free Ba(Ti0.8Zr0.2)O3-(Ba0.7Ca0.3)TiO3 (BZT-BCT) thin films were deposited on Pt/TiO2/SiO2/Si substrates using chemical solution deposition method and then the effect of process parameters were investigated to obtain optimum parameters of these lead-free thin films. The phase was selected near to the morphotropic phase boundary (MPH) to increase the number of polarization directions where rhombohedral and tetragonal phases exist together. In this study, the effect of sintering temperatures on microstructure, dielectric and ferroelectric properties were studied systematically. Among the various high-quality BZT-BCT thin films with uniform thickness, the optimum dielectric and ferroelectric responses were observed for films annealed at 800 oC for 1 h sintering time. The thickness was kept constant for all measurements as 500 nm (triple layered films). Therefore, the average grain sizes were found around 60 nm for samples sintered at 700,750 and 800 oC. BZT-BCT thin films sintered at 800 oC showed effective remnant polarization and coercive field values of 2.9 &micro / C/cm2 and 49.4 kV/cm, together with a high dielectric constant and low loss tangent of 365.6 and 3.52 %, respectively, at a frequency of 600 kHz due to pure perovskite phase showing full crystallization and minimum surface porosity obtained at this temperature.

Fatigue crack growth behavior of AA7050 T7451 aluminum alloy under mode II loading condition in two orientations was investigated. Compact shear specimens were prepared in TL and LT directions. A loading frame for mode II type of loading was manufactured. Using the loading frame and the specimen, KIIC values and mode II fatigue crack growth rates were calculated. Fractographic analysis of the fracture surfaces of both mode II fracture toughness test specimens and mode II fatigue crack growth test specimens were done to examine the effects of mode II load. KIIC values were measured between 1.3 and 1.5 times the KIC values for this alloy. As for mode II fatigue crack growth rates, TL orientation shows the highest mode II fatigue crack growth resistance.

For the last decades usage of aluminium alloys have been increasing tremendously. They have been used in aerospace industry widely and now aluminium alloys are becoming more and more popular in automotive and defense industries. Consequently / successful welding of aluminium alloys gains importance. In this study a research is carried out on eldability of plates having different thicknesses of composition 5754 aluminium and 6063 aluminium in T-fillet geometry using Gas-metal Arc Welding technique. It was aimed to have a successful joint without using pre-weld and post-weld heat treatments. During tests welding current and voltage were the varying parameters as welding speed was held constant. Macro-examinations were performed to see the penetration of the weld metal. It was seen that the type of filler wire greatly effects weld penetration. Hardness tests, tensile tests were done to compare the mechanical properties of the welded joints with different filler wires. Despite having better penetration in 4043 filler wire used weld joints, 5356 filler wire used weld joints had higher tensile strength and ductility. In the second part of the study, a dynamic loading machine was designed and manufactured to see the behavior of the fillet welds under dynamic loading. The amount of stress and strain given to the specimen on this machine was adjustable but can&rsquo / t be measured. The tests that were made with this machine aimed only to compare the number of cycles of specimens before fracture. For dynamic loading tests two groups of specimens were prepared with filler wire 4043 / each group having been welded with different heat inputs. It was aimed to see the effect of welding heat input on service lifes but no significant difference between cycle numbers of specimen groups having been welded with different heat inputs was observed. Microstructure examinations of these specimens revealed that coarsening the grains, grain boundaries, particles in PMZ and HAZ regions between Al 6063 base metal and weld zone made these areas more susceptible and favorable for crack propogation than Al 6063 base metal.

The effect of different aging treatments on fatigue crack growth behavior of AA6013 aluminum alloy was investigated. C(T) (Compact Tension) specimens were prepared in L-T and T-L direction for fatigue crack growth tests. Samples were in T651 as received, T42 which is solution heat treated at 538 &ordm / C for 90 minutes, water quenched and aged in room temperature for 96 hours, and one group of samples were overaged at 245 &ordm / C for 12 hours after T42 condition was achieved. Hardness and conductivity measurements were achieved for all conditions after the heat treatments. Fatigue crack growth tests were performed at as received condition T651, T42 and 245 &ordm / C aged samples in laboratory air with sinusoidal loading of stress ratio R=0.1 and at a frequency of 1 Hz. The highest fatigue crack growth resistance is observed for T651 T-L and 245 &ordm / C overaged L-T condition.

The aim of the study was to investigate the crystallization kinetics and solidification behaviour of Fe60Co8Mo5Zr10W2B15 bulk glass forming alloy. The solidification behaviour in near-equilibrium and non-equilibrium cooling conditions was studied. The eutectic and peritectic reactions were found to exist in the solidification sequence of the alloy. The bulk metallic glass formation was achieved by using two methods: quenching from the liquid state and quenching from the semi-state. Scanning electron microscopy, x-ray diffraction and thermal analysis techniques were utilized in the characterization of the samples produced throughout the study. The choice of the starting material and the alloy preparation method was found to be effective in the amorphous phase formation. The critical cooling rate was calculated as 5.35 K/s by using the so-called Barandiaran and Colmenero method which was found to be comparable to the best glass former known to date. The isothermal crystallization kinetics of the alloy was studied at temperatures chosen in the supercooled liquid region and above the first crystallization temperature. The activation energies for glass transition and crystallization events were determined by using different analytical methods such as Kissinger and Ozawa methods. The magnetic properties of the alloy in the annealed, amorphous and as-cast states were characterized by using a vibrating sample magnetometer. The alloy was found to have soft magnetic properties in all states, however the annealed specimen was found to have less magnetic energy loss as compared to the others.

The aim of this study was to produce zirconium diboride (ZrB2) and other metal borides such as lanthanum hexaboride (LaB6) and cerium hexaboride (CeB6) by magnesiothermic reduction (reaction of metal oxide, boron oxide and magnesium) using volume combustion synthesis (VCS) and mechanochemical process (MCP). Production of ZrB2 by VCS in air occurred with the formation of side products, Zr2ON2 and Mg3B2O6 in addition to MgO. Formation of Zr2ON2 was prevented by conducting VCS experiments under argon atmosphere. Wet ball milling was applied before leaching for easier removal of Mg3B2O6. Leaching in 5 M HCl for 2.5 hours was found to be sufficient for removal of MgO and Mg3B2O6. By MCP, 30 hours of ball milling was enough to produce ZrB2 where 10% of excess Mg and B2O3 were used. MgO was easily removed when MCP products were leached in 1 M HCl for 30 minutes. Complete reduction of ZrO2 could not be achieved in either production method because of the stability of ZrO2. Hence, after leaching VCS or MCP products, final product was composed of ZrB2 and ZrO2. Formation of LaB6 and CeB6 were very similar to each other via both methods. Mg3B2O6 appeared as a side product in the formation of both borides by VCS. After wet ball milling, products were leached in 1 M HCl for 15 hours and pure LaB6 or CeB6 was obtained. As in ZrB2 production, 30 hours of ball milling was sufficient to form these hexaborides by MCP. MgO was removed after leaching in 1 M HCl for 30 minutes and the desired hexaboride was obtained in pure form.

The aim of this study is to develop a theoretical basis and to perform computational experiments for understanding the grain boundary (GB) grooving in polycrystalline thin film metallic conductors (interconnects) by anisotropic surface diffusion due to capillary, electromigration and elastostatic forces. To this end, irreversible thermo&ndash / kinetics of surfaces and interfaces with triple junction singularities is elaborated, and the resulting well-posed moving boundary value problem is solved using the front&ndash / tracking method. To simulate the strain conditions of the interconnects during service, the problem is addressed within the framework of isotropic linear elasticity in two dimensions (plane strain condition). In the formulation of stress induced surface diffusion, not only the contribution due to elastic strain energy density (ESED) but also that of the elastic dipole tensor interactions (EDTI) between the stress field and the mobile atomic species (monovacancies) is considered. In computation of the elastostatic and electrostatic fields the indirect boundary element method (IBEM) with constant and straight boundary elements is utilized. The resulted non&ndash / linear partial differential equation is solved numerically by Euler&rsquo / s method of finite differences. The dynamic computer simulation experiments identify well known GB groove shapes and shed light on their growing kinetics. They also allow generating some scenarios under several conditions regarding to the applied force fields and/or physicochemical parameters. The destruction of groove symmetry, termination of the groove penetration with isotropic surface diffusivity, ridge/slit formations with anisotropic diffusivity and the role played by the wetting parameter are all identified for electromigration conditions. The kinetics of accelerated groove deepening with an applied tensile stress is examined in connection with GB cavity growth models in the literature and a diffusive micro-crack formation is reported at the groove tip for high stresses. On the other hand, the use of EDTI provided a means to dynamically simulate GB ridges under compressive stress fields with surface diffusion. An incubation time for hillock growth and a crossover depth over which GB migration becomes energetically favorable is defined and discussed in this context.

Before beginning the experimental work of this study, a magnesium high pressure die casting facility is set up to manufacture magnesium cast parts for defence industry. In this thesis two components are cold chamber high pressure die casted using magnesium alloy AZ91 as raw material, and one component was manufactured using both aluminium alloy A.413, and magnesium alloy AZ91. Mechanical properties of high pressure die casting parts depend on various parameters such as, thickness of the cast part, position of the cast part in the cavity, molten metal temperature, die temperature, piston speeds, and injection pressure. The aim of this study is to investigate the effects of section thickness of the cast part, position of the cast part in the die cavity, piston speeds, and molten metal temperature on mechanical properties of magnesium die cast parts. Tensile properties of products from Al A.413 and Mg AZ91 alloys are also compared. Casting analysis software is used to simulate filling and temperature evolution of three different casting components. Piston speeds are first calculated from equations in the literature and then verified by using the software. Specimens for microstructural investigation, and mechanical tests are machined directly from the mass produced parts. Optical microscopy, and scanning electron microscopy investigations are carried out for grain size and porosity determination. Tensile tests are conducted for yield strength, ultimate tensile strength, and % elongation values. The results of casting analysis software simulations, grains size investigations, porosity investigations, and tensile tests are correlated to each other. Optimum piston speeds, optimum molten metal temperatures are observed, effect of grain size and porosity concentrations on the effect of mechanical properties are compared. Weight of cast parts produced from Mg AZ91 are 35 % lower than that of Al A.413 parts. However, ultimate tensile strength of the cast parts produced from Mg AZ91 are found to be similar to the aluminium parts.

A study was carried out on the selection of processing condition that would yield Mg-Ti with most favourable hydrogenation properties. Processing routes under consideration were / mechanical milling under inert atmosphere, reactive milling i.e. milling under hydrogen atmosphere, ECAP (equal channel angular pressing) and thermal plasma synthesis. Structure resulting from each of these processing routes was characterized with respect to size reduction, coherently diffracting volume and the distribution of Ti catalyst. Mechanical milling yielded a particulate structure made up of large Mg agglomerates with embedded Ti fragments with a uniform distribution. Mg agglomerates have sizes larger than 100 &micro / m which arises as a result of a balance between cold welding process and ductile fracture. Repeated folding of Mg particles entraps Ti fragments inside the Mg agglomerates resulting in a very uniform distribution. Coherently diffracting volumes measured by X-ray Rietveld analysis have small sizes ca. 26 nm which implies that the agglomerates typically comprise 1011 crystallites. Mechanical milling under hydrogen, i.e. reactive milling, led to drastic reduction in particle size. Mg and Ti convert to MgH2 and TiH2 which are milled efficiently due to their brittleness resulting in particle sizes of sub-micron range. Hydrogenation experiments carried out on Mg-10 vol % Ti milled under argon yields enthalpy and entropy values of -76.74 kJ/mol-H2 and -138.64 J/K.mol-H2 for absorption and 66.54 kJ/mol H2 and 120.12 J/K.mol H2 for desorption, respectively. For 1 bar of hydrogen pressure, this corresponds to a hydrogen release temperature of 280 &deg / C. This value is not far off the lowest desorption temperature reported for powder processed Mg based alloys. ECAP processing is a bulk process where the powders, consolidated in the first pass, have limited contact with atmosphere. This process which can be repeated many times lead to structural evolution similar to that of milling, but for efficient mixing of phases it was necessary to employ multi-pass deformation. An advantage of ECAP deformation is strain hardening of the consolidated powders which has improved milling ability. Based on this, a new route was proposed for the processing of ductile hydrogen storage alloys. This involves several passes of ECAP deformation carried out in open atmosphere and a final milling operation of short duration under inert atmosphere. The plasma processing yields Mg particles of extremely small size. Evaporation of Mg-Ti powder mixture and the subsequent condensation process yield Mg particles which are less than 100 nm. Ti particles, under the current experimental condition used, have irregular size distribution but some could be quite small, i.e. in the order of a few tens of nanometers. Of the four processing routes, it was concluded that both reactive milling and thermal plasma processing are well suited for the production of hydrogen storage alloys. Reactive milling yield particles in submicron range and plasma processing seems to be capable of yielding nanosize Mg particles which, potentially, could be decorated with even smaller Ti particles.