WorldCat Identities

Dirras, Guy

Overview
Works: 34 works in 48 publications in 2 languages and 60 library holdings
Genres: Academic theses 
Roles: Thesis advisor, Opponent, Other, Author
Publication Timeline
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Most widely held works by Guy Dirras
Comportement mécanique et évolutions microstructurales sous compression quasi-statique et dynamique de polycristaux CFC et HC : effet de la taille des grains by Abdelouahab Ouarem( )

4 editions published in 2012 in French and held by 7 WorldCat member libraries worldwide

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
Elaboration des biomatériaux apatitiques nanostructurés en milieux polyols : caractérisations physico-chimiques et études mécaniques après compaction par spark plasma sintering by Abderrahmen Mechay( Book )

5 editions published in 2014 in French and held by 5 WorldCat member libraries worldwide

L'hydroxyapatite est un biomatériau bioactif largement utilisé pour la réparation et la reconstruction des défauts osseux, cependant, son efficacité est souvent limitée par sa faible densité. Le présent travail constitue une nouvelle contribution à l'étude des biocéramiques compacts nanostructurés qui sont considérés comme étant des matériaux facilement implantables au niveau osseux et dentaire. Des nanoparticules anisotropes d'hydroxyapatites ont été synthétisées par hydrolyse forcée en milieu polyol, en vue d'améliorer les caractéristiques mécaniques des biocéramiques apatitiques. Les nanopoudres obtenues ont été consolidées par le processus non-conventionnel tel que le frittage flash (spark plasma sintering, SPS) aboutissant à des massifs d'hydroxyapatites nanostructurés 3D. Ces derniers ont montré des performances morphologiques similaires à celles utilisés dans l'industrie, d'autre part, elles ont montré des performances mécaniques améliorées avec une dureté allant jusqu'à 9 GPa
Modélisation multiéchelle du couplage élastoplasticité-endommagement par décohésion en grandes déformations by Nöel Alain Zontsika( Book )

4 editions published in 2014 in French and held by 5 WorldCat member libraries worldwide

Since decades, the study of mechanical and physical properties of UFG and NC microstructures has considerably increased as well as processing techniques. The growing interest in these materials comes from new behaviors encountered with wide range of applications perspectives in many scientific and technologic engineering fields, with high added value and important economic issues such as microelectronics, telecommunications, aeronautics, energy and army. In mechanics, the growing interest resides in both the possibility of processing microstructures with high mechanical strength and high ductility. However, these last microstructures have shown a very low strain hardening capacity although they were observed to have a high mechanical strength. New deformation mechanisms are suspected to induce these behaviors namely grain size deformation mechanisms which cause Hall-Petch strain profile inversion and/or early damage. Nowadays, there are many techniques to process UFG and NC microstructures with both high mechanical strength and improved strain hardening capacities. Similarly, simulation numerical tools have helped to understand some phenomenon still not accessible via experiments. Boring in mind this last aspect, a micromechanics modeling was proposed in this work to characterize microstructure influence on yield stress and damage and to study the crystalline texture evolution
Mécanismes de déformation et résistance à la rupture des polycristaux à grains ultra-fins études expérimentales et numériques by Lukasz Farbaniec( )

2 editions published in 2012 in French and held by 4 WorldCat member libraries worldwide

The objective of this thesis is to provide insights of two fundamental topics regarding the deformation and failure mechanisms of ultrafine-grained face-centered cubic metals. The first topic considers the mechanisms of plastic deformation as a desired grain fragmentation process in order to achieve a significant refinement of structural elements. For this purpose, the so-called Dynamic Plastic Deformation technique is used to cause the grain refinement of polycrystalline nickel. Subsequently, a Fast Fourier Transform numerical procedure is applied to the microstructure after deformation, and the results are compared with the experiments. The second topic deals with the effect of the stress state on ductile toughness along with identification of the mechanisms leading to tensile failure. To this end, a small-scale experimental and numerical modelling techniques are developed and implemented to predict fracture behaviour of polycrystalline nickel and steel. Consequently, the obtained results are used to formulate a criterion applied to the crack tip situation. The numerical results are compared with the experimental data to validate the procedure and estimate fracture toughness of the investigated material
Polycristaux à grains ultrafins élaborés par métallurgie des poudres : microstructures, propriètés mécaniques et modélisation micromécanique by Quang Hien Bui( Book )

2 editions published in 2008 in French and held by 3 WorldCat member libraries worldwide

The general principles underlying the processing of high strength, and ductile, metallic materials have been understood since the beginning of the development of dislocation theory. If ductility necessitates a reasonable mobility of dislocations, strengthening is related to the building of obstacles restricting their propagation. Within this framework the present work focuses on the effect of grain size. To this end, due to their versatility, powder metallurgy routes such as HIP and SPS have been used to process a wide range of Nickel based microstructures, whose effects on the macroscopic behavior has been studied by quasi static compression tests at room temperature. In parallel, since the grain size alone neither defines the microstructure nor characterizes the mechanical behavior of metallic polycrystals, we have developed a micromechanical model that is based on a generalized self-consistent approach to shed light on the effect of microstructural parameters such as the grain size and its statistical distribution on the macroscopic behavior
Mécanismes de déformation et résistance à la rupture des polycristaux à grains ultra-fins : études expérimentales et numériques by Lukasz Farbaniec( Book )

2 editions published in 2012 in French and held by 3 WorldCat member libraries worldwide

The objective of this thesis is to provide insights of two fundamental topics regarding the deformation and failure mechanisms of ultrafine-grained face-centered cubic metals. The first topic considers the mechanisms of plastic deformation as a desired grain fragmentation process in order to achieve a significant refinement of structural elements. For this purpose, the so-called Dynamic Plastic Deformation technique is used to cause the grain refinement of polycrystalline nickel. Subsequently, a Fast Fourier Transform numerical procedure is applied to the microstructure after deformation, and the results are compared with the experiments. The second topic deals with the effect of the stress state on ductile toughness along with identification of the mechanisms leading to tensile failure. To this end, a small-scale experimental and numerical modelling techniques are developed and implemented to predict fracture behaviour of polycrystalline nickel and steel. Consequently, the obtained results are used to formulate a criterion applied to the crack tip situation. The numerical results are compared with the experimental data to validate the procedure and estimate fracture toughness of the investigated material
Magnesium for biomedical applications as degradable implants : thermomechanical processing and surface functionalization of a Mg-Ca alloy by Olivier Jay( )

1 edition published in 2015 in English and held by 2 WorldCat member libraries worldwide

Since the last decade, degradable implants for bone fixation have attracted special attention. Among different materials, magnesium appears as a promising candidate due to its unique combination of properties. Magnesium is very well tolerated by the body, it has a natural tendency for degradation and its low elastic modulus helps to reduce stress-shielding effect during bone healing. However, an optimal compromise between mechanical resistance and degradability kinetics has to be achieved. Since calcium is biocompatible and has several beneficial effects on magnesium, the alloy selected for this project is: Mg-2wt.%Ca alloy. To optimize this alloy for implant application, we propose a bulk/surface approach: i.e. tailoring the bulk microstructure by thermomechanical treatments and surface functionalization by additive manufacturing.Hot rolling and extrusion, and equal channel angular pressing (ECAP) have been used to tailor the microstructure. Severe plastic deformation induced by the ECAP process produces the finest grain and second particle phase microstructure. While different microstructural features (dislocations, twins, grain size) can account for the increase of the mechanical strength, the evolution of the corrosion resistance appears as primarily affected by grain size and second phase microstructure. This influence results from the combination of a micro galvanic effect, the dispersion of the second phase Mg2Ca and possibly a more stable oxide layer. Finally ECAP appears as the most efficient processing to improve both mechanical and corrosion behavior.Surface functionalization is achieved by designing a surface pattern using microdeposition with silver nanoparticles to add an antibacterial effect. The deposition is followed by a laser sintering process. A series of deposition were performed to optimize the deposition conditions for silver nanoparticles. The layer topography, the sintering, and the thermal impact of the laser treatment on the substrate microstructure have been characterized by profilommetry, SEM, TEM. A finite element simulation has been realized to describe the thermal effect of the laser treatment. This simulation can be further used for optimizing the patterning deposition process.Combining the bulk and surface approach have permitted to obtain a functionalized magnesium alloy with enhanced properties that can be considered for further biomedical tests
Evolutions microstructurales, écrouissage et endommagement de composites à matrices métalliques Fe-TiB₂en chargement montone inversé by Manel Kharrat Dammak( Book )

1 edition published in 2014 in French and held by 2 WorldCat member libraries worldwide

The aim of this work was the plasticity and damage mechanisms analysis of a new steel matrix composites Fe- TiB₂ family to establish the microstructure / mechanical properties relationships then interesting for metal forming simulations in respect with various microstructural parameters. The study was focused on composites with different matrix grain size and a given particle population. The experimental characterization of initial microstructures and textures with SEM/EBSD and XRD permitted the qualitative and quantitative analysis of different morphological parameters of reinforcements and the ferritic matrix. The effect of matrix grain size and reinforcements on the composites hardening is studied based on monotonous and reverse simple shear tests which leads to determine the relative contribution of kinematic hardening. The application of a phenomenological modeling based on these results, has successfully describe the composite backstress evolution. Analysis of the microstructural evolution with shear deformation and with four points bending situ tests has shown a sensitivity of Fe-TiB₂ damage to the matrix grain size, the particles size and to the strain-path change. A damage model of heterogeneous material has been then considered and provides the particles failure stress of on the basis of the available experimental results
Etude expérimentale et théorique de l'effet de la température sur les dislocations dissociées dans Béta-CuZn : lien avec l'anomalie plastique by Guy Dirras( Book )

2 editions published in 1990 in French and held by 2 WorldCat member libraries worldwide

DANS LE CADRE GENERAL DES TRAVAUX SUR LES RAISONS DE LA REMONTEE DE LA LIMITE ELASTIQUE EN FONCTION DE LA TEMPERATURE PRESENTE DANS DE NOMBREUX ALLIAGES ORDONNES, NOUS AVONS ETUDIE L'EFFET DE LA TEMPERATURE SUR LES DISLOCATIONS DISSOCIEES DANS LE LAITON-BETA, DE STRUCTURE B2. POUR CELA, DES MONOCRISTAUX DE LAITON-BETA ONT ETE DEFORME PAR COMPRESSION SUIVANT 001 ET 111 ENTRE LA TEMPERATURE AMBIANTE ET 300C, DE FACON A COUVRIR TOUTE L'ETENDUE DE L'ANOMALIE D'ELASTICITE. LA MICROSTRUCTURE DE DEFORMATION A ETE OBSERVEE AU MICROSCOPE ELECTRONIQUE EN TRANSMISSION, PAR LA TECHNIQUE DU FAISCEAU FAIBLE. ON OBSERVE QUE LES SUPERDISLOCATIONS <111>, DISSOCIEES EN DEUX SUPERPARTIELLES 1/2 <111> BORDANT UNE PAROI D'ANTIPHASE DOMINENT LA MICROSTRUCTURE DANS TOUTE LA GAMME DE TEMPERATURES EXPLOREES, QUOIQUE POUR CERTAINES ORIENTATIONS DE LA CONTRAINTE APPLIQUEE (111 PAR EXEMPLE), LA MICROSTRUCTURE REVELE LA PRESENCE DU GLISSEMENT <010> A LA TEMPERATURE DU PIC. D'AUTRE PART, LA PROPORTION RELATIVE DES DISLOCATIONS MIXTES, DISSOCIEES PAR MONTEE AUGMENTE AVEC LA TEMPERATURE. PARALLELEMENT, LA STRUCTURE ET L'ENERGIE DES PAROIS D'ANTIPHASE DANS LES B2 A ETE CALCULEE EN FONCTION DE LA TEMPERATURE PAR LA METHODE VARIATIONNELLE DES AMAS (C.V.M.). ON OBSERVE AINSI UNE DILUTION PROGRESSIVE DU PROFIL DES PAROIS D'ANTIPHASE AVEC LA TEMPERATURE. DE PLUS, L'ANALYSE DE LA CONTRAINTE NECESSAIRE POUR DEPLACER LA SUPER-DISLOCATION DANS DE TELLES PAROIS MONTRE QUE CELLE-CI PRESENTE UN PIC, QUI DANS LE CAS DU LAITON-BETA A LIEU AUX ENVIRONS DE 200C, EN ACCORD AVEC LES RESULTATS EXPERIMENTAUX
De la nanopoudre aux matériaux denses nanostructurés à base de l'alliage métastable Ni-P : microstructure, comportements magnétiques et mécaniques by Mohamed Ali Bousnina( Book )

1 edition published in 2013 in French and held by 2 WorldCat member libraries worldwide

Des matériaux denses nanostructurés à base de l'alliage métastable Ni-P ont été élaborés par une stratégie "bottom-up" qui combine deux étapes. La première consiste en la préparation de nanoparticules de l'alliage grâce au procédé polyol modifié par l'ajout d'hypophosphite, un agent réducteur fort. Les nanoparticules obtenues sont de morphologie sphérique et de taille variant de 39 à 220 nm. La deuxième étape consiste en la consolidation de ces nanopoudres par le procédé SPS. Les massifs denses obtenus sont constitués de grains polygonaux de nickel (taille variant de 154 à 650 nm) et de nanoparticules sphériques de Ni₃P localisées aux points de jonction triple et aux joints des grains de nickel. Ces nanoparticules de taille ne dépassant pas 250 nm sont formées par un mécanisme de diffusion du phosphore à travers les grains de nickel. Les matériaux denses élaborés présentent les caractéristiques magnétiques d'un ferromagnétisme doux (faible champ coercitif) mais une aimantation à saturation élevée proche de celle du nickel massif. Les propriétés mécaniques sont fonction de la taille des grains. Quand cette taille est faible, les matériaux manifestent une résistance mécanique et une limite élastique élevées accompagnées d'une faible ductilité. Une augmentation de la taille des grains entraine des évolutions inverses conformément à la loi de Hall-Petch
Frittage conventionnel et par induction de composites à base d'argent pour les disjoncteurs de puissance by Edouard Biguereau( )

1 edition published in 2015 in French and held by 2 WorldCat member libraries worldwide

L'amélioration des procédés de fabrication de matériaux de contacts électriques à base d'argent nécessite de mieux comprendre et maîtriser les mécanismes mis en jeu lors du frittage. Ce travail a pour objectif d'identifier et d'expliquer l'influence des paramètres d'élaboration des composites Ag-C-Ni et Ag-WC sur les mécanismes de frittage et les propriétés finales dans le cas d'un frittage conventionnel et par induction.La démarche expérimentale adoptée a consisté à réaliser en parallèle des essais de frittage conventionnel dans un dilatomètre permettant le suivi en continu de la déformation et dans un dispositif de chauffage par induction permettant d'obtenir des vitesses de chauffage élevées. Un intérêt particulier a d'abord été porté à l'influence de la poudre d'argent (morphologie et taux d'impuretés) afin d'identifier les mécanismes de densification de l'argent pur, avant d'étudier l'influence des poudres de renfort (nature, teneur et taille) sur le frittage des composites.L'analyse des résultats de ces essais de frittage a permis de montrer que des phénomènes de gonflement et de densification sont en compétition lors du chauffage. Nous avons déterminé, d'une part, que le gonflement pendant le frittage est le résultat d'un fluage local sous l'effet de la pression à l'intérieur de la porosité fermée, d'autre part, que celui-ci est influencé par la présence et la nature des renforts qui modifient la morphologie et la répartition de la porosité. Quant à la densification elle est induite par les mécanismes classiques de frittage.Enfin nous avons montré que le chauffage rapide par induction, en ne laissant pas assez de temps aux mécanismes de diffusion à longue distance, permet de favoriser les mécanismes de diffusion à courte distance comme la soudure des particules au détriment des mécanismes de densification liés à une diffusion à longue distance. Dans le cas de l'argent et des composites Ag-C-Ni, le frittage par induction permet donc d'atteindre une bonne consolidation avec un gonflement moindre qu'en frittage conventionnel, et d'obtenir ainsi de meilleures propriétés
Polycristaux à grains ultrafins élaborés par métallurgie des poudres microstructures, propriètés mécaniques et modélisation micromécanique by Quang Hien Bui( )

1 edition published in 2008 in French and held by 2 WorldCat member libraries worldwide

The general principles underlying the processing of high strength, and ductile, metallic materials have been understood since the beginning of the development of dislocation theory. If ductility necessitates a reasonable mobility of dislocations, strengthening is related to the building of obstacles restricting their propagation. Within this framework the present work focuses on the effect of grain size. To this end, due to their versatility, powder metallurgy routes such as HIP and SPS have been used to process a wide range of Nickel based microstructures, whose effects on the macroscopic behavior has been studied by quasi static compression tests at room temperature. In parallel, since the grain size alone neither defines the microstructure nor characterizes the mechanical behavior of metallic polycrystals, we have developed a micromechanical model that is based on a generalized self-consistent approach to shed light on the effect of microstructural parameters such as the grain size and its statistical distribution on the macroscopic behavior
La Déformation Plastique Dynamique comme procédé monoétape d'élaboration pour l'optimisation des caractéristiques mécaniques des matériaux de structure : relations microstructure propriétés by Jérôme Mespoulet( )

1 edition published in 2020 in French and held by 1 WorldCat member library worldwide

Dans la famille des alliages de cuivre, le Cu - Be a longtemps été le matériau au compromis de performances conductivité électrique/résistance mécanique le plus élevé. Cependant, en raison de sa toxicité, l'utilisation du Béryllium est devenue contraignante. Des solutions de remplacement portent désormais sur d'autres nuances, de type Cu - Ti, Cu - Ni - Si ou encore Cu - Ni - Sn. Ces derniers n'ont cependant pas encore démontré pleinement leur équivalence. Ainsi, les présents travaux de thèse, qui se sont déroulés dans le cadre du développement de nouvelles microstructures pour répondre aux besoins constants de matériaux performants en conditions hautes pressions fluides (liquide en quasi statique ou gazeux en dynamique), ont permis d'évaluer la capacité du procédé d'élaboration en régime dynamique à élaborer, en une seule étape, des microstructures nouvelles et optimisées, par impact direct à des vitesses de 2250±50s-1 et 4250±50s-1.Les résultats obtenus permettent de dire que les premiers objectifs qui concernaient l'augmentation des propriétés mécaniques macroscopiques ont été atteints pour les deux alliages de l'étude, à savoir Cu - Be et Cu - Ni - Sn. En effet, des gains de ~28 et 23% par rapport aux états initiaux ont été obtenus sans recourir à des ajouts d'éléments d'addition rares, voire stratégiques pour lesquels le marché mondial est contraint (exemples : Ta, V, Nb...). Mieux, l'alliage Cu - Ni - Sn qui est appelé à remplacer, pour l'application envisagée, l'alliage Cu - Be a montré de réels espoirs, quant à sa stabilité microstructurale
Evolutions microstructurales, écrouissage et endommagement de composites à matrices métalliques Fe-TiB₂ by Manel Kharrat Dammak( )

1 edition published in 2014 in French and held by 1 WorldCat member library worldwide

The aim of this work was the plasticity and damage mechanisms analysis of a new steel matrix composites Fe- TiB₂ family to establish the microstructure / mechanical properties relationships then interesting for metal forming simulations in respect with various microstructural parameters. The study was focused on composites with different matrix grain size and a given particle population. The experimental characterization of initial microstructures and textures with SEM/EBSD and XRD permitted the qualitative and quantitative analysis of different morphological parameters of reinforcements and the ferritic matrix. The effect of matrix grain size and reinforcements on the composites hardening is studied based on monotonous and reverse simple shear tests which leads to determine the relative contribution of kinematic hardening. The application of a phenomenological modeling based on these results, has successfully describe the composite backstress evolution. Analysis of the microstructural evolution with shear deformation and with four points bending situ tests has shown a sensitivity of Fe-TiB₂ damage to the matrix grain size, the particles size and to the strain-path change. A damage model of heterogeneous material has been then considered and provides the particles failure stress of on the basis of the available experimental results
De la nanopoudre aux matériaux denses nanostructurés à base de l'alliage métastable Ni-P : microstructure, comportements magnétiques et mécaniques by Mohamed Ali Bousnina( )

1 edition published in 2013 in French and held by 1 WorldCat member library worldwide

Dense nanostructured materials based on the metastable Ni- P alloy were prepared by "bottom- up" strategy. This synthesis pathway is the combination of two steps. The first is to prepare the powder by soft chemistry (reduction in polyol medium modified by the addition of hypophosphite a strong reducing agent). The nanoparticles produced have spherical morphology and size ranging from 39 to 220 nm. These powders are metastable solid solutions Ni- P. The second step is to consolidate these powders by SPS process; it results in dense nanostructured material consisting of polygonal grains of nickel (size ranging from 254 to 650 nm) along with spherical nanoparticles Ni3P located at triple junction points and grain boundaries. These nanoparticles of size no greater than 250 nm are formed by a diffusion mechanism through the phosphorous nickel grains. The as-obtained dense materials have magnetic characteristics of a soft ferromagnetism (low coercivity) but a good saturation magnetization close to that of bulk nickel. These materials also exhibit very interesting mechanical properties depending on the grain size. When the grain size is small, the materials exhibit mechanical strength and high elastic limit accompanied by low ductility. An increase in grain size leads to inverse changes in line with the Hall-Petch law
Alliages réfractaires à forte entropie : comportement mécanique sous sollicitations complexes, mise en place d'une nouvelle voie d'élaboration by Vasuki Kentheswaran( )

1 edition published in 2019 in English and held by 1 WorldCat member library worldwide

From Japanese sabres to modern aircraft engines alloying elements have been used to enhance mechanical properties. Adding alloying elements to a main constituent enables to achieve a desired microstructure or to combine mechanical properties. High-entropy alloys, namely multicomponent metallic alloys, break with the past traditional approach since they contain several major elements in equiatomic or quasi-equiatomic proportions resulting in a single-phase disordered solid solution stabilised by its configurational entropy increased with the number of constituents, hence the name of such alloys. High-entropy alloys blaze a trail to new alloy design strategies and new type of metallic materials. The enthusiasm of the scientific community has been triggered by the oustanding mechanical properties of these alloys and particularly upon combining antagonist properties such as strength and ductility. Refractory high-entropy alloys are very promising materials for high temperature applications and need to be characterised upon various types of loading before considering them for potential applications. Process and characterisation are considered in the framework of this thesis. Under dynamic loading, the studied refractory high-entropy alloys with BCC structure exhibited either a thermal softening behaviour or a work-hardening behaviour. Fatigue endurance ratio has an oustanding level of 0.43 under four-point bending fatigue loading. The other aspect investigated in this study is the ability to process these alloys by powder metallurgy route and especially by Self-propagating High temperature Synthesis (SHS) and Spark Plasma Sintering (SPS)
Contribution à la compréhension des liens entre microstructure et propriétés tribologiques d'aciers inoxydables haute dureté après traitements de surface by Edson thiago Silva santos( )

1 edition published in 2015 in French and held by 1 WorldCat member library worldwide

Des industriels du domaine aéronautique se sont regroupés autour du projet MEKINOX (Mécanique Inoxydable) visant à développer l'utilisation de différentes nuances d'aciers inoxydables en raison de leur haute résistance mécanique et de leur résistance à la corrosion. Cependant ces aciers sont réputés sensibles au frottement. Dans ce contexte, ce travail de thèse est dédié dans un premier temps à l'étude de l'effet des différents traitements thermiques et de surface sur la microstructure des aciers inoxydables visant à améliorer leur aptitude au frottement. Nous avons mis en évidence différents mécanismes de durcissement : par précipitation, par changement de phase et par solution solide. Dans un deuxième temps, nous avons mis en place une démarche expérimentale permettant de comparer la réponse des différents couples de matériaux sous contact roulant et glissant extrêmes. Ces essais nous ont permis de caractériser l'évolution du coefficient de traction et de classer les différents états métallurgiques selon leur résistance à l'usure. Dans un troisième temps, nous avons caractérisé les différents types d'endommagements se produisant en surface et en sous-couche. Enfin, l'utilisation de l'EBSD nous a permis caractériser la déformation plastique en sous couche et de tenter de corréler la valeur de la densité de HAGB (Angles à forte désorientation) avec la résistance à l'usure des différents états métallurgiques des aciers étudiés
Tungstène et alliages nanostructurès dans le système W-V-Cr pour la fusion : synthèse, densification et propriétés mécaniques by Sarah Dine( )

1 edition published in 2018 in French and held by 1 WorldCat member library worldwide

The aim of this thesis concerns the synthesis of nanostructured tungsten and tungsten alloys, related to the thermonuclear fusion issue, with a double perspective, one concerning the powders themselves,in order to simulate the dust that will be produced during the tokamak operation, the other concerning bulk materials, where the nanostructure could bring a significant improvement on mechanical properties (elastic limit, ductility), and also on specific properties related to this operating environment (resistance to sputtering, blistering, corrosion, ...).To do so, we synthesized tungsten and binary and ternary alloys in the W-V-Cr system using Selfpropagating High-temperature Synthesis. These powders were then sintered using Spark Plasma Sintering, in order to retrieve bulk dense samples. At each step of the process, the materials were characterized using X-Ray Diffraction, Scanning Electron Microscopy, Energy Dispersive Spectroscopy, microhardness and compression tests. Our results show that we were able to obtain bulk nanostructured samples, with a relative density ranging from 97 to 100% depending on the alloy, with an elastic limit of up to 1000 MPa and a ductility of about 30%, which is a very promising results for a tungsten alloy with no rhenium
Traitement thermomécanique de l'alliage Ti17 : Forgeage en alpha + bêta et maintien post-forgeage en bêta by Mélanie Semblanet( )

1 edition published in 2014 in French and held by 1 WorldCat member library worldwide

La présente thèse s'inscrit dans un contexte d'optimisation des procédés de forgeage et de traitements thermiques des alliages de titane pour les pièces de moteurs Snecma.Les sociétés TIMET, élaborateur, et SNECMA, motoriste, ont identifié des enjeux très analogues concernant le forgeage des billettes en alliage de titane destinées à la fabrication de disques moteurs. Il est nécessaire d'acquérir une maîtrise complète de la gamme de transformation, de la coulée au produit final. Ce traitement thermomécanique comporte une alternance d'étapes de forgeage dans les domaines bêta, à haute température, et alpha + bêta, à basse température.L'objectif est de déterminer expérimentalement et de modéliser le comportement mécanique ainsi que les évolutions de microstructure de l'alliage Ti17 au cours d'une déformation dans le domaine alpha + bêta suivie d'un maintien en bêta.En amont, ces travaux mènent à une meilleure compréhension des facteurs qui influencent la taille de grain dans le domaine bêta : la taille de grain bêta initiale, les orientations des aiguilles alpha dans le grain, la déformation et la désorientation subies lors du forgeage en alpha + bêta, etc.En ce qui concerne les applications, ils s'intègrent à un post-processeur métallurgique dédié au forgeage des alliages de titane, qui utilise les histoires thermomécaniques issues d'un calcul par éléments finis
Etude de l'influence des impuretés dans des microalliages de cuivre sur leurs microstructures et leurs propriétés mécaniques by Romain Savina( )

1 edition published in 2014 in French and held by 1 WorldCat member library worldwide

This study takes place in the context of electric wires production using waste copper. Oxygen and sometimes lead are present in small amount in these products. We decide to study their influence on the microstructure and mechanical properties. After studying the influence of oxygen and lead on the microstructure using the binary phase diagram Cu-O and the ternary phase diagram Cu-O-Pb, we focused our work on the influence of these impurities on mechanical properties. In-situ tensile tests have been carried out on samples at different chemical compositions inside the SEM chamber to observe the evolution of microstructure during déformation. Before each deformation test, EBSD analysis has been achieved to make the identification of cracks localization easier and acquire several parameters that can have an influence on mechanical properties (texture, Schmid factor...). These tests show important differences on mechanical properties and craking mechanism according to various factors that we indentify (temperature, porosity, grain boundary misorientation, precipitation....)
 
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G. Dirras Frans onderzoeker

Guy Dirras

Guy Dirras forsker

Guy Dirras researcher, ORCID id # 0000-0002-2201-7132

Languages
French (32)

English (2)