Dissertations / Theses on the topic 'Microstructure (physique) – Évolution'
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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
Baud, Sandrine. "Frittage en phase liquide du carbure de silicium : évolution des microstructures et des propriétés mécaniques : Etude thermodynamique des interactions oxydes/SiC." Grenoble INPG, 2000. http://www.theses.fr/2000INPG4201.
Davoisne, Carine. "Évolution des silicates dans les milieux interstellaires, circumstellaires et cométaires : Le rôle de l'irradiation et de la température." Lille 1, 2006. https://pepite-depot.univ-lille.fr/RESTREINT/Th_Num/2006/50376_2006_98.pdf.
Vivier, Florian. "Fluage à 500°C d'un joint soudé d'un acier 9Cr-1Mo modifié - Evolution de la microstructure et comportement mécanique." Phd thesis, École Nationale Supérieure des Mines de Paris, 2009. http://tel.archives-ouvertes.fr/tel-00399352.
Des essais de vieillissement thermique, de traction et de fluage à 450°C et 500°C, sur du métal de base et du joint soudé ont été réalisés. Différentes géométries d'éprouvettes de fluage de joint soudé ont été testées. Aucune évolution significative de la microstructure n'a été constatée en termes de nature et de taille de précipités et de dimension de la sous-structure par rapport à la microstructure avant essai. Peu d'endommagement par cavitation a pu être mis en évidence. Le mécanisme qui conduit à la ruine finale du matériau après fluage est de type viscoplastique à 500°C, contrairement à 625°C où l'endommagement par cavitation est la cause principale de la rupture des éprouvettes de fluage pour les temps d'exposition les plus longs.
A partir des courbes expérimentales de fluage du métal de base et du joint soudé entier, un modèle phénoménologique de comportement de type Norton à 500°C est proposé. L'exposant de Norton du métal de base est de 19, alors que celui du joint soudé entier est de 18. Ces valeurs suggèrent la présence de contraintes internes et indiquent que le glissement des dislocations peut être le mécanisme qui contrôle la déformation par fluage. Les éprouvettes de joint soudé cassent dans le métal fondu en fluage et dans le métal de base en traction. La zone affectée thermiquement n'a pas de rôle visible dans la résistance de la structure à 500°C, du moins jusqu'à 4500 h. De ce fait, une décomposition en série du comportement en fluage du joint soudé entier peut être faite à l'aide de ceux du métal fondu et du métal de base. Connaissant le comportement du métal de base et du joint soudé entier, il est possible d'ajuster les paramètres du modèle au métal fondu. Une autre méthode d'ajustement des paramètres du métal fondu est également proposée à partir des essais sur une géométrie amincie contenant uniquement du métal fondu. Les résultats de ces modèles sont cohérents avec les données de la littérature. Ce modèle permet de prédire le temps à rupture à plus long terme, en bon accord avec des résultats du CEA, avec des outils simples de modélisation.
Pignol, Valérie. "Évolution et caractérisation de structures cellulaires bidimensionnelles expérimentales, en particulier les mousses de savon, et simulées." Phd thesis, Institut National Polytechnique de Lorraine - INPL, 1996. http://tel.archives-ouvertes.fr/tel-00717860.
Chen, Cai. "Textures et microstructures dans l'aluminium, le cuivre et le magnésium après hyperdéformation." Thesis, Université de Lorraine, 2016. http://www.theses.fr/2016LORR0061.
Severe plastic deformation (SPD) is an efficient technique to transform the microstructure of bulk metals into ultra fine grained structure with grain sizes less than 1 µm or even into nanostructure with nano-grains of less than 100 nm in diameter. The very small grain size attributes excellent mechanical properties to the material. In present thesis work, two recently developed SPD techniques, namely, High Pressure Tube Twisting (HPTT) and Cyclic Expansion and Extrusion (CEE) were performed on different metallic materials at room temperature. Details of fragmentation of microstructure and metallographic texture evolution were investigated by electron backscattered diffraction (EBSD), transmission electron microscopy (TEM), transmission kikuchi diffraction (TKD) and X-ray diffraction (XRD). Shear strain gradient across the thickness of the HPTT deformed Al tube sample was found by a local shear measurement method. This shear strain gradient induced the inhomogeneity of microstructure and texture in HPTT deformed pure Al, solid solution alloy Al-4%Mg and pure Mg. The microhardness and average grain size in different zones as a function of shear strain were measured. The limiting steady grain sizes in the steady state for these different materials produced by HPTT were 700 nm, 100 nm and 900 nm, respectively. The texture evolution of pure Mg in HPTT up to a shear strain of 16 was simulated in simple shear using the self-consistent (VPSC) polycrystal model and showed good agreements with the experimental results measured by XRD. Based on the measured disorientation distribution function in HPTT deformed Al, a new technique for the magnitude of local shear strain in SPD was proposed. This new technique was applied to a protrusion produced in twist extrusion (TE) and to an Al sample deformed in free-end torsion. Cu and pure Al samples were intensively deformed by the CEE SPD technique. The microstructure and texture evolutions were measured by EBSD, showing a gradient from the center-zone to the edge part of the rod sample. The texture evolution of CEE deformed Cu was simulated by the VPSC polycrystal model using a flow line function. The simulation results confirmed the experimental texture features observed in the CEE process. The tensile testing behavior of large strain torsion pre-processed Cu was examined. In spite of the shear strain gradient existing in the bar, a technique was proposed to obtain the tensile stress-strain curve of such gradient material
Batista, dos Santos Marcio Wagner. "Investigation of the mechanical behaviour and microstructural evolution of titanium alloys under superplastic and hot forming conditions." Thesis, Ecole nationale des Mines d'Albi-Carmaux, 2017. http://www.theses.fr/2017EMAC0013/document.
This thesis was developed in the frame of a Brazil-France cooperation agreement between the École des Mines d'Albi-Carmaux and the Polytechnic School of Engineering of the University of Sao Paulo (EPUSP). It aims to contribute to the study of the mechanical behaviour of Ti6Al4V alloys especially in terms of superplastic forming. The general objective of this research is to develop non-conventional forming processes for new titanium alloys applied to aerospace components. Therefore, in accordance of the equipment’s available in the two groups, the work will be conducted either at the Ecole des Mines d'Albi-Carmaux and either at EPUSP. This thesis aims to answer questions such as what are the implications in relation to the microstructural and mechanical behaviour of these alloys during superplastic and hot forming in order to establish a behaviour law for these alloys based on titanium. This requires a good knowledge of the properties of materials used in the superplastic and hot forming domain to control the parameters governing the phenomenon of superplasticity or high temperature plasticity. For this, a testing strategy and characterization methodology of those new titanium alloys was developed. The tests include high temperature uniaxial tensile tests on several Ti6Al4V alloys showing different initial grain sizes. Special focus was made on the microstructural evolution prior to testing (i.e. during specimen temperature increase and stabilization) and during testing. Testing range was chosen to cover the hot forming and superplastic deformation domain. Grain growth is depending on alloy initial microstructures but also on the duration of the test at testing temperature (static growth) and testing strain rate (dynamic growth). After testing microstructural evolutions of the alloys will be observed by optical micrograph or SEM and results are used to increase behaviour model accuracy. Advanced unified behaviour models where introduced in order to cover the whole strain rate and temperature range: kinematic hardening, strain rate sensitive and grain growth features are included in the model. In order to get validation of the behaviour model, it was introduced in ABAQUS numerical simulation code and model predictions (especially macroscopic deformation and local grain growth) were compared, for one of the material investigated, to axisymmetric inflation forming tests of sheet metal parts, also known as bulge test. To obtain a simple control cycle, tests performed at IPT/LEL laboratory in San José Dos Campos in Brazil were operated with a constant strain rate. Results show a very good correlation with predictions and allows to conclude on an accuracy of the behaviour models of the titanium alloys in industrial forming conditions
Jouanny, Emilie. "Étude de l'évolution microstructurale sous irradiation aux ions Ti2+ de deux alliages de titane : lien avec les propriétés mécaniques." Thesis, Université de Lorraine, 2017. http://www.theses.fr/2017LORR0071/document.
This PhD work deals with microstructural evolution of titanium alloys under irradiation, due to their potential use in the nuclear field. Parametric study (temperature, dose and irradiation flux) was conducted, using ion irradiations (JANNuS – Saclay platform) to simulate neutron irradiation damage. Two titanium alloys (CP Ti grade 2 and Ti-6Al-4V) were considered and qualitative and quantitative post irradiation microstructural characterizations were done (TEM, image analysis, APT). Thus, various irradiation defects were identified. In particular, presence of -component loops was highlighted in CP Ti grade 2 and vanadium-rich precipitates in Ti-6Al-4V from the temperature of 300°C. Resulting microstructure is hardly depending on irradiation parameters and considered titanium alloys. Important effect of temperature (between 300°C and 430°C) was noted on -type dislocation loops in CP Ti grade 2 and precipitates in Ti-6Al-4V. At 300°C, dose and flux have no effect on the defect distribution of the two titanium alloys. At 430°C, the increase of dose has a little consequence on the -type dislocation loops in Ti-6Al-4V, contrary to the ones observed in CP Ti grade 2. Precipitates, observed in Ti-6Al-4V, do not seem to be affected by the increase of the dose. Analysis of involved mechanisms is proposed. Finally, nano-indentation tests have allowed to get first description of the link between microstructure and mechanical properties. At 430°C, CP Ti grade 2 do not seem to be affected mechanically by the microstructural evolution with the irradiation dose, contrary to Ti-6Al-4V
Ouarem, Abdelouahab. "Comportement mécanique et évolutions microstructurales sous compression quasi-statique et dynamique de polycristaux CFC et HC : effet de la taille des grains." Paris 13, 2012. http://scbd-sto.univ-paris13.fr/intranet/edgalilee_th_2012_ouarem.pdf.
The present work is devoted to the analysis of the strain rate and grain size effects on the deformation mechanism activated during plastic deformation of two polycrystalline materials: (i) zinc (Zn), a crystal with hexagonal compact packing structure, having grain size in the micro and ultrafine grain ranges (~ 300 µm and 200 nm, respectively), loaded under quasi-static and dynamic compression conditions, up to a strain rate of ~ 10⁵ s⁻¹ (by use of a Direct Impact Hopkinson Pressure Bars (DIHPB); (ii) electrodeposited nickel (Ni), a face-centered cubic structure with grain size of 5 µm deformed in compression under dynamic conditions using DIHPB. Significant differences in terms of micro-mechanisms of deformation in the two regimes were found: (i) At lower strain rates, up to ~ 10² s⁻¹, dislocation-based plasticity was observed in both Ni and Zn. Extensive twinning occurred only in the case of micrometer grain-sized Zn, indicating a grain size dependence of twinning; (ii) In the dynamic regime (> 10³ s⁻¹) plastic deformation induced a significant increase of the temperature within the samples. This increase of temperature was significant enough to induce recovery and/or dynamic recrystallization. As consequence two phenomena were observed depending on the structure under investigation: for Ni, the resulting microstructure and mechanical properties were similar to that of the initial state, dominated by annealing twins and equiaxed and randomly oriented grains. For micro-grained Zn a tremendous grain refining was found. As a consequence, twinning was inhibited. To clarify this point, additional investigations were carried out on coarse-grained CP-Ti deformed in both quasi-static and dynamic regimes. It was found that twinning was the main deformation mechanism. Indeed, the larger the strain rate and grains size, the larger the twin density. On the one hand, these results clearly demonstrate the grain size effect on the occurrence of mechanical twinning in HCP materials. On the other hand, the effect of the strain rate on twinning was found to depend on the material under investigation. Compared to Ti, the lower homologous temperature T/T m of Zn probably plays a key role, as it may induce dynamic recovery/recrystallization as far as the present experimental conditions are concerned
Mandolini, Tommaso. "Microstructural evolution of polymineralic aggregates deformed under high pressure and temperature : an in-situ and post-mortem study on olivine+serpentine." Electronic Thesis or Diss., Université de Lille (2022-....), 2022. http://www.theses.fr/2022ULILR047.
At plate tectonic boundaries, the lithosphere is deformed and strain localization occurs up to kilometers-scale, which can manifest in form of shear zones. The strain localization suggests the strength of the lithosphere is locally weakened. The formation of interconnected layers of weaker minerals in the lithosphere is a potential mechanism to achieve such weakening. Serpentinized peridotite is commonly found within and between tectonic plates. It is mainly composed of olivine and serpentine minerals. The latter is generally accepted to be weaker than olivine at geological strain rates. During deformation, strain is thus expected to preferentially partition into serpentine than into olivine. This can lead to the formation of interconnected weak layers (IWL) of serpentine where strain localizes.The present work is based on microstructural investigation to infer the strain accommodation in rocks. Olivine+serpentine aggregates with two compositions (10 and 20 vol.% serpentine) are used as a proxy for partially serpentinized peridotites. The aggregates are experimentally deformed in torsion at high pressures (HP, > 2 GPa) and high temperatures (HT, > 300°C) at an equivalent strain rate of 10-4 s-1. The experiments are coupled with in-situ absorption contrast X-ray tomography. I obtain 2D and 3D information on connectivity and structural layering in the microstructure of the ‘weak' serpentine. Electron microscopy is performed on recovered samples to link the in-situ X-ray tomography observations to the plastic properties of the phases.I first outline experimental and image-data processing procedures specific to in-situ HP experimental deformation. Then, I study the deformation of the aggregates with increasing shear deformation at multiple scales of observations. The main aim is to observe the onset and development of IWL in its microstructure. The relations between the morphology and plastic properties of the phases in the rock are investigated to understand the strain localization in serpentinized peridotite.The main results show the deformation regime in olivine+serpentine aggregates can be described as semi-brittle, with the dominant phase of olivine (‘stronger') mainly displaying brittle deformation, whereas the serpentine (‘weaker') showing a dominant ductile-style deformation. A strain γ of ca. 4-5, serpentine content of ca. 20 vol.%, and initial fraction of large clusters >15 vol.% determine the condition for IWL configuration in the olivine+serpentine aggregates. Conversely, at serpentine content of ca. 10 vol.%, IWL do not occur, independently of strain or initial clusters size distribution of serpentine. This is more consistent with a load-bearing framework (LBF) behavior, where the stronger olivine grains are jammed, and during deformation crush one another, leading to grain size reduction and accommodating much of the deformation in the rock. These findings suggest contents of serpentine >10 vol.% or ca. 20 vol.% define a threshold for crucial changes in the morphology, connectivity, percolation, of the weak serpentine in serpentinized peridotites under shear. This may lead to important changes in deformation behavior and mechanical properties of the rock.In light of these findings, I give some perspectives for strain localization and shear zones initiation in the lithosphere
Fall, Ameth Maloum. "Etude de la rhéologie à chaud et des évolutions microstructurales de l'alliage Ti-5553." Thesis, Saint-Etienne, EMSE, 2015. http://www.theses.fr/2015EMSE0801/document.
Ti-5553 alloy used for landing gear manufacturing has a complex thermomechanical diagram during hot working process which consists of successive forging steps in the single phase β and the two phase α+β regions. For this purpose, in order to optimize theTi-5553 forging process in Messier-Bugatti-Dowty Company, significant development of knowledge of rheology and the microstructural evolution during thermomechanical processing is necessary. The aims of this work are: i) to find out experimentally the rheology, ii) to model the mechanical behavior, and iii) to characterize the microstructural changes during different strain sequences in theα+β and β regions.Uniaxial compression tests were carried out in order to determine the rheology of the Ti-5553 alloy in the single and the two-phase region. The latter provide the behavior of the alloy in the two initial states, “billet” and “as forget”. This information was used to determine the rheological behavior of the material in the temperature range 720 to 990 ˚C, strain rate range 0.001 to 1 s-1 and strains in the range 0.1 to 1.2. A rheological model of the material behavior based on Hansel-Spittle equations was proposed which takes into account the dependence of the flow behavior of the material with strain rate and temperature.Moreover, characterisation methods such as optical, scanning electron microscopies, X-rays and EBSD analyses were used to examine the microstructures in the initial state (undeformed) and the deformed material. These techniques allowed the measurement of alpha and beta grain sizes as well as the texture of the material at different conditions (undeformed and deformed material). The results also indicated that a dynamic α-phase precipitation phenomenon in the material can take place during the hot working process
Chang, Hui. "Transformations de phase et évolutions des microstructures dans l'alliage de titane beta Ti-B19." Thesis, Vandoeuvre-les-Nancy, INPL, 2010. http://www.theses.fr/2010INPL053N/document.
The phase transformations and microstructure evolutions has been characterized for different thermal treatments, and the relationships between final microstrures and properties have been investigated in the new metastable Ti-B19 alloy. The isothermal phase transformation kinetics and the influence of different heat treatment phaths have been establisheb by using in-situ electrical Resistivity. The structures have been determined by synchrotron X-Ray Diffraction and the microstructures were observed by SEM and TEM. The results show that phase transformation kinetics and microstructure characteristics are strongly dependent on the aging temperature (ranging from 300 to 700°C). The global isothermal phase transformation phase transformation kinetics has been got and anallyzed with JMAK equation, and the TTT diagram of Ti-B19 alloy has been established. We have also shown that the heating rate has remarkable influence on the isothermal phase transformation behaviors and the pre-deformation accelerates the transformation kinetics. The microstructure evolutions during cooling are obviously dependent on the cooling rates. A first attempt has been made to calculate the transformation kinetics during cooling using JMAK law and Scheil principle. Finally, the relationship between mechanical properties and microstructure has been discussed
Da, Costa Teixeira Julien. "Études expérimentales et modélisation des évolutions microstructurales au cours des traitements thermiques post forgeage dans l'alliage de titane Ti17." Vandoeuvre-les-Nancy, INPL, 2005. http://www.theses.fr/2005INPL027N.
The mechanical properties of the Ti 17 alloy are strongly linked to the size, the morphology and the distribution of the a precipitates inside the 13 matrix. These micro structural parameters are dependent on the thermomechnical treatment applied to the part. Thus the control of the mechanical properties and the improvement of the processes goes through the knowledge of the final microstructure as weIl its evolution when applying these processes. For this purpose, two modeling approaches are developed, in the case of the thermal treatment following the high temperature forging: The first approach lies on the Johnson - Mehl- Avrami - Kolmogorov (JMAK) law, which allows the prediction of each a phase morphology amount, at a macroscopic scale. The metallurgical calculation needs the prior measurement of the isothermal transformation kinetics, in order to determine the JMAK law parameters. Controlled cooling treatments are simulated, the comparison with the experiment being conclusive. The case of large parts with temperature and microstructure gradients is then treated. The thermophysical data of the aIloy and the transformation enthalpy are first measured, and coupled temperature and microstructure evolutions are predicted with the Finite Element calculation software ZeBuLoN, inside which we implemented our metallurgical model. The simulation results are compared to experimental results obtained for large cylinders equipped with thermocouples during the cooling. The obtained modelling tool is then applied to an industrial piece. The second approach lies on the modeling of the nucleation and growth of the a precipitates on the grain boundaries. This calculation at the microscopic scale of the precipitates allows to predict the influence of the plastic defOrination in the high temperature 13 phase field. The model uses 13 microstructure parameters after the deformation (for instance the size of recristallized grain), in function of the deformation conditions. Transformation kinetics are predicted for several temperature controlled treatments, following either a simple solution treatment or a plastic deformation at given conditions. Concerning the influence of a prior plastic deformation, the comparison with experimental results in the literature is conclusive. Moreover, the model is useful for other aIloys (knowledge of the equilibrium phases composition and of the diffusion coefficients) and it allows to accede to micro structural parameters as the precipitate size
Alwan, Raad Aboud. "Analyse des évolutions structurales et du comportement mécanique d'un acier au chrome-nickel-molybdène à très bas carbone du type Z1CNDA 12-09-02, en fonction des traitements thermiques." Paris 11, 1989. http://www.theses.fr/1989PA112002.
We have studied the structural behavior of a stainless steel capable of age hardening, with a very low carbon content. The martensitic alloy concerned by this research has the following composition : Fe-11. 7 Cr-9. 2 Ni-1. 99 Mo-0. 71 Al-0. 34Ti. The thermal treatments have been undertaken in the temperature range of -160°C and 1150°C. The kinetics of the austenitic transformation and the volumic fraction of reversed austenite stabilizes at ambient temperature have been caracterized as a function of the treatment conditions (isothermal and/or isochronal). During isothermal tempering three stages of hardening may occure before the overaging phenomenon and the formation of reversed austenite. Finally, interesting mechanical properties (Rm and R0. 002) and the improvement of A % and KCV for this alloy, can be obtained when the tempering is performed in the range of 525-550°C, the increase in ductility and toughness being obtained to the detriment of a small decrease in mechanical proof
Le, Baillif Paul. "Prise en compte des évolutions de la précipitation gamma prime dans la modélisation du comportement mécanique en traction du PER72® au cours du traitement thermique : application à la prévision des contraintes résiduelles après trempe." Thesis, Ecole nationale des Mines d'Albi-Carmaux, 2018. http://www.theses.fr/2018EMAC0013.
PER72® is a nickel-base superalloys developed by Aubert & Duval. This alloy is used in helicopter engine turbine disk manufacturing. During the elaboration, a heat treatment provides the alloy his good mechanical properties, but it can also be at the origin of residual stress that can affect the disk capabilities.The objective of this work is to study the heat treatment and formulate mechanical behaviour law in order to estimate residual stress generated during the process. The heat treatment conditions are studied. On one hand, the effect of cooling rate on mechanical properties is investigated. On the other hand, for each studied cooling rate, the quench is interrupted at a testing temperature to carry out a tensile test. A special testing device has been developed in order to carry out the heat treatment of alloy specimens directly on the testing machine. Moreover, for each testing condition, the microstructure is characterized. In particular, precipitate size and volume fraction have been measured. The first objective is to understand the influence of quenching conditions on mechanical properties and microstructure. A link between the microstructure and the mechanical properties is then discussed. Finally, a thermo-mechanical behaviour law is formulated. This model takes the identified microstructural parameters into account
Monaco, Federico. "Analyse de la dégradation des cellules à oxydes solides fonctionnant en mode pile à combustibles et électrolyse : évolution microstructurale et stabilité des matériaux d'électrodes." Thesis, Université Grenoble Alpes, 2020. http://www.theses.fr/2020GRALI034.
This work was dedicated to the analysis of the degradation of solid oxide cells operated in electrolysis and fuel cell modes. A threefold methodology has been applied by coupling (i) electrochemical tests, (ii) advanced post-test analyses and (iii) multi-scale modeling. Long-term durability experiments have been carried out on standard cells (Ni-YSZ/YSZ/GDC/LSCF) to investigate the performance loss as a function of the operating conditions. Specimens, which have been extracted from the pristine and aged samples, have been characterized to evaluate the microstructural and physico-chemical evolutions occurring at the two electrodes. In parallel, detailed micro-kinetic models for the hydrogen electrode (Ni-YSZ cermet) and for the oxygen electrode (LSCF/LSCF-GDC) have been developed and experimentally validated before being integrated into a macro-scale model for the complete cell. The multi-scale numerical tool has been used to propose a better understanding of the underlying forces driving the degradation. Moreover, the impact on the cell performances has been simulated and discussed as a function of the operating conditions. Based on the results presented in this work, it has been confirmed that the degradation of SOCs is significantly larger in electrolysis mode with respect to fuel cell operation under H2. On the one hand, it has been shown that the difference in durability behavior can be ascribed to the effect of the cathodic overpotential on the nickel instability in the hydrogen electrode. On the other hand, it has been observed and demonstrated that the destabilization of the LSCF is favored by both the anodic current and the high operating temperature
Maury, Nicolas. "Influence de la microstructure initiale sur les évolutions microstructurales au cours du revenu et du vieillissement dans l'alliage de titane ß-métastable Ti-17." Thesis, Université de Lorraine, 2018. http://www.theses.fr/2018LORR0125.
This PhD work is about the study of the formation of bimodal microstructures by solid-solid phase transformations and their evolutions during subsequent heat treatments, especially the one that simulates a long-term ageing in use, in the β-metastable titanium alloy Ti-17. Various initial dual-phase αprimary + βmetastable microstructures were formed from the β phase field, with significant differences in the phase microstructural parameters (fraction, size, density, spatial distribution) and chemical compositions. The influence of these initial microstructures and the heat treatment parameters (heating rate, duration and temperature of isothermal holding) on the kinetics and sequences of phase transformations during short-term ageing was then studied by means of in-situ characterisation techniques (electrical resistivity, synchrotron X-ray diffraction). Multi-scale microstructural characterisations (XRD, SEM, TEM-EDX) were coupled with quantification tools developed to precise the evolutions of the microstructural parameters and the chemical compositions during isothermal holding, in order to establish links with the mechanical properties and hardness. The complementarity of these means used eventually enabled to determine the transformation temperature domains of metastable phases (ωisothermal and α''isothermal), of which the kinetics and quantity vary with the heating rate and the initial microstructure. These differences have consequences on the resulting microstructure, in particular concerning the size and the density of the αsecondary grains. The phase chemical compositions were determined and compared to those calculated at thermodynamic equilibrium. Finally, the subsequent microstructural (increase in the α phase fraction, precipitation of the ordered α2 phase) and chemical (compositions that tend towards the ones at equilibrium) evolutions during a long-term thermal ageing were investigated and correlated to the evolutions of the mechanical properties
Di, Napoli Paolo. "Modélisation des évolutions microstructurales par changement de phases dans les alliages de titane [bêta] - métastables." Thesis, Vandoeuvre-les-Nancy, INPL, 2010. http://www.theses.fr/2010INPL070N/document.
A model has been developed which is able to predict the kinetics of beta → alpha transformation in industrial multi component titanium alloys during complex heat treatments. The model is based on: (i) a simple geometric representations of the different morphologies commonly observed in these alloys (parent α grains, α allotriomorphs (at grain boundaries), αcolonies and intragranular α precipitates); (ii) analytical nucleation and growth laws for each morphology of α phase; (iii) the assumption of local equilibrium at interfaces, handled within the CalPhaD framework; (iv) averaged solute balances in each morphology. Diffusion of solutes in both phases is considered. We thus obtain the transformation kinetics as well as mean size parameters and mean chemical composition for each morphology of the product α phase (at grain boundaries, colonies and intragranular precipitates. Calculations performed are at first presented for a ternary TiVO alloy emphasizing the potentialities of the model. The relationships between growth conditions, role of diffusion in each phase, and chemical composition for each morphology are analyzed upon isothermal holdings, cooling from the beta phase field and more complex cooling-heating sequence. The model is further used on the Ti17 industrial and results are compared to experimental transformation kinetics and microstructures
Dylewski, Benoît. "Caractérisation expérimentale multi-échelles et multi-techniques du rail prélevé en service : de la déformation plastique sévère et des évolutions de microstructure à l'amorçage de fissures par Fatigue de Contact de Roulement." Electronic Thesis or Diss., Compiègne, 2016. http://www.theses.fr/2016COMP2324.
This work is dedicated to the characterization of severe plastic deformation and microstructure evolution induced in rails in service, leading to cracks initiation by Rolling Contact Fatigue. Initiation of these surface cracks and in-depth propagation involve several phenomena at the microstructure scale which can lead to surface spalling at the macroscopic scale or even to brutal failure of the rail during its service. To improve understanding of these various phenomena beneath the rail surface, an experimental, multi-scales and multi-techniques methodology has been followed on rails removed from service. In the first part of results, the presence of a three-dimensional gradient of microstructure, of crystallography and of mechanical properties induced by the repeated contacts with wheels has been highlighted in a rail head during its service. Then, by means of a field analysis campaign of rails removed from service at several accumulated loads, the different stages of in-depth gradients development and plastic deformation accumulated in the rail head have been estimated in relation with total accumulated tonnage and cracks initiation. This study contributes to improve the understanding of the damage mechanisms in rolling contact fatigue of rails in service and the modeling of rail plasticity and crack propagation by including anisotropy of the running band and effect of in-depth microstructure evolution
Ben, Haj Slama Meriem. "Étude multi-échelle et in situ des évolutions microstructurales en conditions isothermes d’aciers bainitiques en lattes." Thesis, Université de Lorraine, 2018. http://www.theses.fr/2018LORR0042/document.
Bainitic steels are widely used in industry thanks to their good combinations of strength, toughness and ductility. Meanwhile, after obtaining the targeted microstructure, the steel can undergo additional isothermal holdings (either during manufacturing and/or during usage) prone to degrade its properties. The thesis work aims at understanding the microstructural origins of this degradation. To achieve this, we applied controlled heat treatments on model FeNiC and FeNiMnC steel grades. A first set of heat treatments allowed us to obtain different microstructures; upper and lower bainites, martensite and mixed concepts. These transformation products were characterized and analyzed in detail, particularly by EBSD with improved angular resolution. Data was operated to reconstruct prior austenitic grains and to distinguish the different transformation products according to their crystallographic variant spatial organization. A second set of heat treatments consisted in aging these microstructures by extended isothermal holdings. We show that lath-like bainitic microstructures are not stable under certain isothermal conditions. In the most advanced cases, we observed a « granularization » process of the lath microstructure, associated with high misoriented variant disappearance and carbides ripening. These phenomena were observed for the studied model alloys, even within short holding times (<1h) and at low temperatures (300°C). These highlighted evolutions as well as their kinetics were investigated at different scales, coupling SEM observations, EBSD, TEM and in situ XRD High Energy on large instruments. The initial microstructure and the steel chemical composition affect significantly the « granularization » kinetics. But we have above all put the light on the major role of the presence of an upper bainite fraction (even a residual one) in the initial microstructure, to start the granularization phenomenon, independently of aging temperature. All of these results allow discussing possible mechanisms with their respective driving forces and opening larger discussion about bainite classification
Tioual-Demange, Sarah. "Modélisation d’évolutions microstructurales dans les alliages de titane." Electronic Thesis or Diss., Université de Lorraine, 2019. http://www.theses.fr/2019LORR0293.
The present study is mainly about the calculation of β → α + β transformation kinetics and the prediction of resulting microstructures in three industrial titanium alloys Ti17, Ti6242 and Ti6246 and a ternary alloy TiMoO during isothermal heat treatments, by pursuing the development of TITAN model, developed by Di Napoli (2010). A study of the sensitivity of the model to several input parameters is first presented, distinguishing two temperature domains: the domain of morphologies at the grain boundaries αgb + αwgb , and the domain of the intragranular morphology αwi. Among these parameters: the critical thickness of appearance of awgb morphology and the spacing between the lamellae, in order to determine a dataset for the different alloys and temperatures studied; the σββ grain boundary energies, which have a significant influence on the nucleation and growth of the three α phase morphologies; the aspect ratio of the αwi spheroids, which varies according to the isothermal holding temperature; the thermodynamic parameters and diffusivities of the alloying elements, which control the thermodynamic equilibrium, and whose study allowed to highlight complex evolutions. The influence of the isothermal holding temperature and the alloy composition on phase transformation kinetics has also been addressed. These studies allowed to establish a calculated TTT of Ti17 alloy, in agreement with the experimental results