Littérature scientifique sur le sujet « Microstructure (physique) – Évolution »
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Thèses sur le sujet "Microstructure (physique) – Évolution":
Lance, Dominique. « Frittage de l'alumine alpha submicronique : nouvelle relation dilatométrie/évolution microstructurale ». Saint-Etienne, EMSE, 2004. http://www.theses.fr/2004EMSEA004.
The microstructural evolutions of pure and doped (Mg, Ti, Zr or Y) submicronic a alumina green bodies have been monitored during overall sintering under non-isothermal conditions with a simple and fast method. Densification rate curves as a function of relative density are definitely more suitable for the description of microstructural evolution than shrinkage rate as a function of temperature. The shape of those curves is very sensitive to initial microstructure (agglomeration state, pore size / particle size ratio) and heating schedule (pre-heating treatment, variation of heating rate). A simple dilatometric run with a modified heating rate is suggested to control the quality of the initial alumina powder
Labonne, Mathilde. « Frittage et évolution microstructurale de carbures cémentés NbC-Ni ». Thesis, Université Grenoble Alpes, 2020. http://www.theses.fr/2020GRALI056.
For more than 70 years, WC-Co materials have been used worldwide for numerous applications in tooling, mining equipment or wear parts. Unfortunately, it has been recently determined that the cobalt and tungsten oxides present risks and health issues. Furthermore, the worldwide demand for tungsten and cobalt has been continuously growing, although the mining stocks of both elements are limited, which increased their price over the years. This global context has led industrial companies to investigate alternative carbide based materials. Niobium carbides are increasingly considered to replace tungsten carbides for specific applications. Although those carbides present a slightly lower hardness, they have impressive wear properties and are twice less dense than WC. Furthermore, no particular health hazards were identified for the use of bulk metallic niobium, niobium carbides and niobium oxides. Previous studies of NbC based materials have mostly focused on their microstructures and the resulting mechanical properties, notably the hardness, toughness and wear properties. However, the sintering process of niobium carbide based cemented carbides and the carbide grain growth mechanism involved have not yet been fully investigated. The present study aims to analyze the sintering behavior and grain growth of NbC-Ni materials and the effect of secondary carbides addition. It was first determined that the carbon content has a significant impact on the sintering behavior and the microstructural evolution. Notably, increasing the carbon content decreases the carbide phase contiguity. The addition of secondary carbides leads to a delay of solid state sintering and limits grain growth. The contiguity increases with these additions. Finally, a particular focus was made on grain growth mechanism in such materials. By combining classic growth theories and a simplified model, it was estimated that growth kinetics are controlled by a cooperative migration of grain boundaries and phase boundaries
Fréchard, Sophie. « Comportement dynamique et évolution microstructurale d'aciers inoxydables austénitiques alliés à l'azote ». Vandoeuvre-les-Nancy, INPL, 2003. http://www.theses.fr/2003INPL030N.
Enault, Sébastien. « Évolution et diversité des structures minéralisées chez les sélaciens : approche paléo-développementale ». Thesis, Montpellier, 2015. http://www.theses.fr/2015MONTS234/document.
Chondrichthyans exhibit a number of interesting features which make them valuable organisms to investigate from an evo-devo perspective. However, due to their cartilaginous skeleton, isolated teeth are usually the only available fossil material to reconstruct their evolutionary history. Their teeth are covered by enameloid, a hypermineralized tissue whose microstructure has proven a useful taxonomic tool to differentiate between modern forms (neoselachians) and their extinct relatives. However it is poorly known in several groups, thus casting doubts on the validity of such characters.In this work, I first describe the enameloid microstructure of batoids based on an extensive sampling of both their extant and extinct diversity. I highlight unexpected diversity in the microstructural organization of enameloid which was thought to be very stable in neoselachians. The developmental basis for this diversity was then investigated in two extant chondrichthyan models through classic histological techniques and in situ hybridization. The results highlight differences in their enameloid organic matrix, as well as important differences with enameloid formation in osteichthyans, casting doubts on the homology of the two tissues. Finally I investigate skeletogenesis in the lesser spotted catshark from both a morphological and molecular perspective. Using X-Ray microtomography and in situ hybridization, I highlight both the mineralization sequence of the cartilaginous skeleton and the molecular context in which it calcifies over the course of embryonic development. I find that skeletal calcification in chondrichthyans appears to be much more versatile than in osteichthyans
Hugonnet, Brice. « Frittage et évolution de la microstructure au cours des traitements thermiques d'aimants NdFeB : influence sur les propriétés magnétiques ». Thesis, Université Grenoble Alpes (ComUE), 2016. http://www.theses.fr/2016GREAI079/document.
NdFeB hard magnets are the most powerful magnets commercially available. Their outstanding properties originate from Nd2Fe14B intrinsic properties and from the microstructure imposed by the manufacturing process. These magnets are generally obtained by liquid phase sintering of an oriented monocrystalline powder which enables a microstructure made of grain magnetically decoupled by a thin neodymium-rich layer which is optimally distributed in the magnet after a low temperature annealing. For them to be used in electrical engines and generators, dysprosium is usually added so that the coercivity is high enough at the working temperature. But dysprosium is rare and expensive and lowers the remnant induction. It is therefore important to get free of its usage by a better understanding of the links between the manufacturing process and the microstructure, so that the final magnetic properties can be optimized.First, this thesis deals with NdFeB sintering on an alloyed commercial grade. The high shrinkage anisotropy during densification is not clearly explained and its interpretation could bring information on the magnetic properties. Dilatometric studies have been performed along orientation direction as well as along the transverse direction. Sintering has been interrupted at different times and the microstructure was observed. Image analysis has enabled to understand, thanks to an analytical model, that a part of the anisotropy could be explained by an anisotropic contact orientation distribution, originating from the magnetic orientation step. Discrete element modelling has confirmed this approach.The second part of the thesis deals with the role of the most commonly used alloying elements on the magnetic properties: aluminum, cobalt and copper. Around twenty different model grades were examined with composition close to the ones of commercial magnets. After having been sintered, the samples were annealed at temperatures deduced from DSC measurements. Results show that the three elements have cross effects on coercivity. Beyond coercivity, demagnetizing curve shape is sensitive to the composition and annealing temperature and gives important information on the role of the alloying elements on the microstructure
Cosson, Benoît. « Modélisation et simulation numérique du procédé de soufflage par bi-orientation des bouteilles en PET : évolution de microstructure, évolution de comportement ». Phd thesis, Université Paris-Est, 2008. http://tel.archives-ouvertes.fr/tel-00470534.
Maetz, Jean-Yves. « Évolution de la microstructure d’un acier inoxydable lean duplex lors du vieillissement ». Thesis, Lyon, INSA, 2014. http://www.theses.fr/2014ISAL0008/document.
Lean duplex stainless steels are austeno-ferritic steels with lower nickel and molybdenum contents, developed in the late 90's. Considering mechanical properties, corrosion resistance and cost of raw material, this family is an interesting alternative to standard austenitic stainless steels, which currently represent two thirds of stainless steel production. However, lean duplex steels are relatively recent and their thermal stability has been relatively little studied, especially during long term aging. In this study, the microstructural evolution of a lean duplex steel 2101 was studied during isothermal aging at temperatures between 20 °C and 850 °C, from few minutes to several months. Aging kinetics were followed by thermoelectric power measurements (TEP), from which aged states were selected to be characterized by electron microscopy and atom probe tomography. At intermediate temperatures of 350 - 450 °C, Fe-Cr demixing and precipitation of Ni-Mn-Al-Si-Cu occur in the ferrite despite the low nickel content of this grade, leading to an increase in the TEP. For higher temperatures, at about 700 °C, the mechanisms which govern the different microstructural evolutions have been described by a multi-scale approach: the nucleation and growth of M23C6 and Cr2N, observed from few minutes of aging and the σ phase precipitation, observed for longer aging time. The latter is accompanied by a transformation of δ ferrite in γ2 secondary austenite, and by the partial transformation of austenite into martensite during cooling. The effect of different phases on the TEP of the lean duplex steel can be qualitatively described during aging by a rule of mixture
Voicu, Raluca. « Évolution microstructurale à haute température et propriétés mécaniques d'aciers austénitiques Fe-Cr-Ni ». Toulouse, INPT, 2008. http://www.theses.fr/2008INPT132G.
The HP40-Nb modified austenitic stainless-steels are used for reformer tubes fabrication in the refining, petrochemical and fertilizer industries, and especially by Air Liquide for cracking reaction of hydrogen. These tubes are the main components of hydrogen production plants. The tubes are designed for exploitation duration of around 11 years. Nevertheless, the operation of the facilities under more severe conditions leads to a greatly decreases the lifetime of these components. These tubes are prone to various degradation mechanisms. The combination of factors such as local overheating, a complex stress field (induced by the heat, the internal gas pressure and weight of the tubes), a corrosive environment inside and an oxidant atmosphere outside of the tubes can lead to premature rupture, braking of these parts. The objective of this study is to understand the coupling between the microstructural aging and mechanical behaviour in creep regime in order to establish a new criterion for end of life of reformer tubes. Microstructural examinations of aged structures have allowed to highlight the effect of several important factors, like the chemical composition and the environment, and to establish a TTT diagram for these steel grades. The systematic study of the creep mechanical behaviour has enabled to identify several factors that influence the lifetime of these alloys, like aging and a change of creep mechanism when passaging from high to low stress levels. Metallographic observations and quantification of the damage confirmed the creep tests results. A criterion for the end of life has been established by integrating these data. Finally, we proposed two thermal loading protocols to optimize the time to rupture of these tubes
Arlazarov, Artem. « Évolution des microstructures et lien avec les propriétés mécaniques dans les aciers 'Médium Mn' ». Thesis, Université de Lorraine, 2015. http://www.theses.fr/2015LORR0086/document.
During the intercritical annealing of fully martensitic Medium Mn steel, containing from 4 to 12 wt.% Mn, the formation of austenite happens through the so-called “Austenite Reverted Transformation” (ART) mechanism. In this PhD work, the evolution of both microstructure and tensile properties was studied as a function of holding time in the intercritical domain. The microstructure evolution was studied using a double experimental and modeling approach. The final microstructure contained phases of different natures (ferrite (annealed martensite), retained austenite and fresh martensite) and of different morphologies (lath-like and polygonal). A particular attention was paid to the kinetics of austenite formation in connection with cementite dissolution and to the morphology of the phases. A mechanism was proposed to describe the formation of such microstructure. The critical factors controlling thermal austenite stability, including both chemical and size effects, were determined and discussed, based on the analysis of the retained austenite time-evolution. At last, tensile properties of the steel were measured as a function of holding time and the relation between microstructure and mechanical behavior was analyzed. Advanced analysis of the individual behavior of the three major constituents was performed. As a final output of this work, a complete model for predicting the true-stress versus true-strain curves of medium Mn steels was proposed
Julien, Renaud. « Comportement thermomécanique et évolution microstructurale d'un alliage Ti-6Al-4V forgé α+β, durant la trempe : expérimentations, analyses et modélisation ». Thesis, Ecole nationale des Mines d'Albi-Carmaux, 2017. http://www.theses.fr/2017EMAC0001/document.
This research is part of the TiMaS project (Titanium Machining and Simulation). The main goal of this project is to develop an analysis and optimization tool of the global production process to control and assess the generation of residual stresses for titanium alloys structures parts. Residual stresses can be generated during thermal and mechanical treatment quenching steps. The main goal of this work is to study the mechanical behaviour and the microstructural evolution of Ti-6Al-4V alloy, induce by quenching from the α+β phase field, and incorporate these results in a modelling approach. For this purpose, a new experimental facility, using conventional hydraulic testing machine and induction heating, was developed to investigate the mechanical behaviour of Ti-6Al-4V alloy under different thermal and mechanical loads. This experiment has permitted to realise tensile/relaxation/tensile tests. Furthermore, an image analysis protocol was developed to study fraction of α and β phases and αII lamellae thickness. Microstructural observations can explain some aspects of the material hardening during quenching. Two mechanical behaviour models were proposed to assess the mechanical behaviour of the Ti-6Al-4V alloy. The first one is an elasto-visco-plastic model with isotropic hardening that taking account of the static recovery. It can predict the mechanical behaviour under different quenching rates. The second one is a non-unified model based on a phases mixing law. It permits a better assessment of the mechanical behaviour and allows the modelling of the yield point phenomenon by using mobile dislocations motion