Nickel-based superalloys and tool steels are well-known high-performance alloys due to their extensive use in many different industries. Nickel-based superalloys have found their way into aircraft, aerospace, marine, chemical, and petrochemical industries owing to their excellent high-temperature corrosion and oxidation resistance. On the other hand, tool steels could provide a combination of outstanding corrosion and wear resistance. They can play an important role in cutting and wear applications and manufacturing plastic extrusion and food processing components. Near-net shape manufacturing using powder metallurgy (PM) and hot isostatic pressing (HIP) can serve as an efficient manufacturing process to produce these alloys. This technology can successfully tackle conventional manufacturing challenges of highly alloyed materials i.e. segregation during the casting process or cracks during hot working processes of Ni-based superalloys, and carbide segregation and formation of large and irregularly shaped carbides in wrought and hot rolled tool steels. However, the presence of precipitates on prior particle boundaries (PPBs) in Ni-based superalloys, and metallurgical defects like non-metallic inclusions in both Ni-based superalloys and tool steels may affect the fatigue performance of these PM-HIPed products. This licentiate thesis aims to investigate the microstructure and fatigue behavior of two PM-HIPed alloys i.e. Inconel 625 and high-nitrogen tool steel. The results confirm precipitation along PPBs in PM-HIPed Inconel 625; however, no effect was detected in the fractography studies of the high cycle fatigue samples, and tensile properties were comparable with wrought materials reported in the literature. On the other hand, the microstructure of PM-HIPed high-nitrogen tool steel displayed dispersed precipitates and no traces of PPBs. Moreover, in both cases, i.e. very high cycle fatigue of PM-HIPed high-nitrogen tool steel and high cycle fatigue of PM-HIPed Inconel 625, fatigue crack initiation was attributed to the presence of non-metallic inclusions, either individually or agglomerated with precipitates. This underscores the significance of the manufacturing process in fatigue performance. / Near-net shape manufacturing using powder metallurgy (PM) and hot isostatic pressing (HIP) can serve as an efficient manufacturing process to produce high-performance alloys. Among the variety of engineering alloys, Nickel-based superalloys and tool steels stand out as well-known high-performance alloys, widely employed across diverse industries. PM-HIP technology can successfully address conventional manufacturing challenges associated with highly alloyed materials, such as segregation during the casting process or cracks during hot working processes of Ni-based superalloys, and carbide segregation and the formation of large and irregularly shaped carbides in wrought and hot rolled tool steels. However, the presence of precipitates on prior particle boundaries in Ni-based superalloys, and metallurgical defects like non-metallic inclusions in both alloys, may affect the fatigue performance of these PM-HIPed products. The present study aims to assess two PM-HIPed alloys, namely Inconel 625 and high-nitrogen tool steel, with a comprehensive examination of their microstructure and fatigue properties. The objectives include examining the microstructural features introduced by the PM-HIP process and understanding how they influence fatigue failure mechanisms in these alloys.

Estimating mass changes of ice sheets or of the global ocean from satellite gravimetry strongly depends on the correction for the glacial isostatic adjustment (GIA) signal. However, geophysical GIA models are different and incompatible with observations, particularly in Antarctica. Regional inversions have resolved GIA over Antarctica without ensuring global consistency, while global inversions have been mostly constrained by a priori GIA patterns. For the first time, we set up a global inversion to simultaneously estimate ice sheet mass changes and GIA, where Antarctic GIA is spatially resolved using a set of global GIA patterns. The patterns are related to deglaciation impulses localized along a grid over Antarctica. GIA associated with four regions outside Antarctica is parametrized by global GIA patterns induced by deglaciation histories. The observations we consider here are satellite gravimetry, satellite altimetry over Antarctica and Greenland, as well as modelled firn thickness changes. Firn thickness changes are also parametrized to account for systematic errors in their modelling. Results from simulation experiments using realistic signals and error covariances support the feasibility of the approach. For example, the spatial RMS error of the estimated Antarctic GIA effect, assuming a 10-year observation period, is 31% and 51%, of the RMS of two alternative global GIA models. The integrated Antarctic GIA error is 8% and 5%, respectively, of the integrated GIA signal of the two models. For these results realistic error covariances incorporated in the parameter estimation process are essential. If error correlations are neglected, the Antarctic GIA RMS error is more than twice as large.Highlights We present a globally consistent inversion approach to co-estimate glacial isostatic adjustment effects together with changes of the ice mass and firn air content in Greenland and Antarctica. The inversion method utilizes data sets from satellite gravimetry, satellite altimetry, regional climate modelling, and firn modelling together with the full error-covariance information of all input data. The simulation experiments show that the proposed GIA parametrization in Antarctica can resolve GIA effects unpredicted by geophysical modelling, despite realistic input-data limitations.

Résumé : L'interaction entre la β-Lactoglobuline (β-Lg) et le rétinol ou entre les micelles de phosphocaséines (PC) et le rétinol à un pH proche de la neutralité, a été étudiée à pression atmosphérique et sous pression isostatique jusqu'à 400 MPa. Les constantes de dissociation et le nombre de sites de liaison ont été calculés indiquant des différences d'affinité en fonction de la structure protéique. A 25°C, des pressions inférieures à 150 MPa favorisent l'association β-Lgrétinol (rapport molaire β-Lg/rétinol : 1/1). A ≥ 150 MPa le complexe se dissocie. A 350 MPa, la β-Lg est dénaturée et le complexe irréversiblement dissocié. Le complexe PCrétinol (rapport molaire PC/rétinol : 1/1) reste au contraire formé après un traitement à 400 MPa et 25°C, bien que la pression induise des phénomènes de dissociation/réassociation des assemblages micellaires à ≥ 100 MPa. L'interaction PCrétinol stabiliserait plutôt les micelles de PC vis-à-vis de la pression, de même qu'une température de pressurisation modérée (35°C) comparativement à une température plus basse (15°C). Un isolat protéique de lactosérum (IPL) en dispersion dans l'eau à 10% (p/p) de protéines (pH 6,5) et en présence d'acétate de rétinol (AcRet) (rapport molaire β-Lg/AcRet : 10/1) a été traité par (i) haute-pression isostatique (HP) (350 MPa, 25°C, 15 min), (ii) traitement thermique de courte durée (TTCD) (75°C, 4 s) ou (iii) homogénéisation à ultra-haute pression (UHPH) (300 MPa, Tin = 24°C). Les trois traitements permettent de former des agrégats de β-Lg capables de retenir l'acétate de rétinol, mais avec une efficacité différente dépendant probablement des mécanismes d'agrégation induit par le chauffage (TTCD), la pression isostatique (HP) ou dynamique (UHPH). Des dispersions à 2,38% (p/p) en phosphocaséines (pH 6,6) en présence d'acétate de rétinol (rapport molaire PC/AcRet : 5/1) ont été traitées par (i) HP (300 MPa, 14°C ou 34°C, 15 min), ou (ii) UHPH (300 MPa, Tin = 14°C). Ces deux traitements favorisent la rétention de l'acétate de rétinol par les micelles de PC pouvant ainsi servir de cargo pour véhiculer des molécules bioactives. Mots clefs : haute pression isostatique, haute pression dynamique, homogénéisation à ultra-haute pression, fluorescence, β-Lactoglobuline, micelles de phosphocaséines, rétinol, acétate de rétinol, agrégats protéiques, interaction protéine-ligand. / Abstract: The binding of retinol to native β-Lactoglobulin (β-Lg) or phosphocasein (PC) micelles at pH close to neutral was studied at atmospheric pressure or under isostatic high-pressure. The dissociation constants and number of binding sites were calculated indicating that difference in retinol affinity depended on protein structure. At 25°C, pressure level < 150 MPa promoted β-Lgretinol association (β-Lg/retinol molar ratio: 1/1). At ≥ 150 MPa, the complex dissociated. At 350 MPa, β-Lg was denatured and the complex irreversibly dissociated. PC and retinol (PC/retinol molar ratio: 1/1) remained associated after pressurisation at 400 MPa and 25°C, while pressure induced dissociation/reassociation phenomena of micelle assemblies. The binding of retinol to PC stabilised micelles towards pressure, as well as moderate temperature of pressurisation (35°C) compared to lower temperature (15°C).A whey protein isolate (WPI) dispersed in water at 10% (w/w) proteins (pH 6.5) in the presence of retinyl acetate (RetAc) (β-Lg/RetAc molar ratio: 10/1) was processed by (i) isostatic high-pressure (HP) (350 MPa, 25°C, 15 min), (ii) short-time thermal treatment (STTT) (75°C, 4 s) or (iii) ultra-high pressure homogenisation (UHPH) (300 MPa, Tin = 24°C). All processing produced β-Lg aggregates able to retain RetAc, but with different efficiency depending on aggregation mechanisms induced by heating (STTT), isostatic high-pressure (HP) or dynamic high-pressure (UHPH). Phosphocaseins dispersed at 2.38% (w/w) proteins (pH 6.6) in the presence of RetAc (PC/RetAc molar ratio: 5/1) were processed by (i) HP (300 MPa, 14°C or 34°C, 15 min), or (ii) UHPH (300 MPa, Tin = 14°C). Both treatments promoted RetAc retention by phosphocasein micelles that can be used as cargoes to transport bioactive molecules.Keywords: isostatic high-pressure, dynamic high-pressure, ultra-high pressure homogenisation, fluorescence, β-Lactoglobulin, phosphocasein micelles, retinol, retinyl acetate, protein aggregates, protein-ligand binding.Discipline: Biochimie, Chimie et Technologie des Aliments.Thèse préparée à : Université Montpellier 2 – Equipe de Biochimie et Technologie Alimentaire – UMR IATE 1208 – Pôle EVAP – Place E. Bataillon, 34095 Montpellier, France.

Glacial isostatic adjustment (GIA) is the process by which the solid Earth responds to past and present-day changes in glaciers, ice caps, and ice sheets. This thesis focuses on vertical crustal motion of the Earth caused by GIA, which is influenced by several factors including lithosphere thickness, mantle viscosity profile, and changes to the thickness and extent of surface ice. The viscosity of the mantle beneath Antarctica is a poorly constrained quantity due to the rarity of relative sea-level and heat flow observations. Other methods for obtaining a better-constrained mantle viscosity model must be investigated to obtain more accurate GIA model predictions. The first section of this study uses seismic wave tomography to determine mantle viscosity. By calculating the deviation of the P- and S-wave velocities relative to a reference Earth model (PREM), the viscosity can be determined. For Antarctica mantle viscosities obtained from S20A (Ekstrom and Dziewonski, 1998) seismic tomography in the asthenosphere range from 1016 Pa∙s to 1023 Pa∙s, with smaller viscosities beneath West Antarctica and higher viscosities beneath East Antarctica. This agrees with viscosity expectations based on findings from the Basin and Range area of North America, which is an analogue to the West Antarctic Rift System. Section two compares bedrock elevations in Antarctica to crustal thicknesses, to infer mantle temperatures and draw conclusions about mantle viscosity. Data from CRUST 2.0 (Bassin et al., 2000), BEDMAP (Lythe and Vaughan, 2001) and specific studies of crustal thickness in Antarctica were examined. It was found that the regions of Antarctica that are expected to have low viscosities agree with the hot mantle trend found by Hyndman (2010) while the regions expected to have high viscosity are in better agreement with the trend for cold mantle. Bevis et al. (2009) described new GPS observations of crustal uplift in Antarctica and compared the results to GIA model predictions, including IJ05 (Ivins and James, 2005). Here, we have generated IJ05 predictions for a three layered mantle (viscosities ranging over more than four orders of magnitude) and compared them to the GPS observations using a χ2 measure of goodness-of-fit. The IJ05 predictions that agree best with the Bevis et al. observations have a χ2 of 16, less than the null hypothesis value of 42. These large values for the best-fit model indicate the need for model revisions and/or that uncertainties are too optimistic. Equally important, the mantle viscosities of the best-fit models are much higher than expected for West Antarctica. The smallest χ2 values are found for an asthenosphere viscosity of 1021 Pa•s, transition zone viscosity of 1023 Pa∙s and lower mantle viscosity of 2 x 1023 Pa∙s, whereas the expected viscosity of the asthenosphere beneath West Antarctica is probably less than 1020 Pa∙s. This suggests that revisions to the IJ05 ice sheet history are required. Simulated annealing was performed on the ice sheet history and it was found that changes to the recent ice load history have the strongest effect on GIA predictions. / Graduate

Robust preconditioners on block-triangular and block-factorized form for three types of linear systems of two-by-two block form are studied in this thesis. The first type of linear systems, which are dense, arise from a boundary element type of discretization of crack propagation problems. Numerical experiment show that simple algebraic preconditioning strategies results in iterative schemes that are highly competitive with a direct solution method. The second type of algebraic systems, which are sparse, indefinite and nonsymmetric, arise from a finite element (FE) discretization of the partial differential equations (PDE) that describe (visco)elastic glacial isostatic adjustment (GIA). The Schur complement approximation in the block preconditioners is constructed by assembly of local, exactly computed Schur matrices. The quality of the approximation is verified in numerical experiments. When the block preconditioners for the indefinite problem are combined with an inner iterative scheme preconditioned by a (nearly) optimal multilevel preconditioner, the resulting preconditioner is (nearly) optimal and robust with respect to problem size, material parameters, number of space dimensions, and coefficient jumps. Two approaches to mathematically formulate the PDEs for GIA are compared. In the first approach the equations are formulated in their full complexity, whereas in the second their formulation is confined to the features and restrictions of the employed FE package. Different solution methods for the algebraic problem are used in the two approaches. Analysis and numerical experiments reveal that the first strategy is more accurate and efficient than the latter. The block structure in the third type of algebraic systems is due to a fine-coarse splitting of the unknowns. The inverse of the pivot block is approximated by a sparse matrix which is assembled from local, exactly inverted matrices. Numerical experiments and analysis of the approximation show that it is robust with respect to problem size and coefficient jumps.

Les travaux exposés dans cet ouvrage décrivent la synthèse, la caractérisation microstructurale et les propriétés physiques de solutions solides nanolamellaires des phases MAX. Les phases Mn+1AXn (M : métal de transition, A : un métal des groupes IlIA ou IV A, et X: carbone ou azote) constituent une famille de nitrures et de carbures ternaires (n = 1 à 3), qui possèdent les meilleures propriétés des métaux et les meilleures propriétés des céramiques.Lors d'une première étape, nous nous concentrons sur la synthèse de solutions solides pures et denses de Ti2AICxNy par compression isostatique à chaud. Les variations des paramètres de maille sont étudiée et discutée an fonction du taux de substitution (carbone-azote) et du taux de lacune (sur le site X). Lors d'une seconde étape, nous étudions les propriétés mécaniques et les propriétés de transport électronique des solutions solides Ti2AICxNy et des phases Ti2AICx et Ti2AINy. La technique de nanoindentation pour déterminer la dureté et le module élastique en fonction du taux de substitution et de lacune. Nous démontrons que la substitution conduit à une amélioration des propriétés mécaniques tandis que l'introduction de lacune conduit à une détérioration de ces propriétés. La résistivité électrique augmente lorsque des lacunes et/ou un effet de substitution sont introduits. Dans le cas de la substitution, nous démontrons que le désordre introduit est faible et que seule la diminution du temps de relaxation explique l'augmentation de la résistivité (interaction électron-phonons). Dans le cas de l'introduction de lacunes, nous montrons que ces dernières conduisent à une modification du temps de relaxation et probablement à une modification de la densité de porteurs.Enfin, l'anisotropie des propriétés de transport électronique a été mise en évidence par des mesures de résistivité réalisée avec le courant électrique circulant dans le plan de base et avec le courant électrique circulant selon l'axe c. Nous démontrons les propriétés de transport dans le plan de base peuvent être comprises en utilisant un modèle à une bande et un mécanisme de conduction assuré par des électrons ayant le comportement de trous. / The work discussed in this thesis concerns the synthesis, the microstructural characterization and the physical properties of nanolaminated MAX phase's solid solution. The Mn+1AXn phases (M: transition metal, A: IlIA or IV A group element, and X: either carbon or nitrogen) are a class of ternary nitrides and carbides (n=l to 3), which possess sorne of the best properties ofmetal and sorne of the best properties of ceramics.In a first step, we focus on the synthesis of highly pure and dense Ti2AICxNy solid solutions by hot isostatic pressing. The influence of the substitution of C atoms by N atoms and the influence of vacancy content on the solid solution lattice parameters is discussed. In a second step, we investigate the mechanical and transport properties of Ti2AICxNy solid solutions and oftheir related Ti2AICx and Ti2AINy end-members. Hardness and elastic modulus has been studied using nanoindentation tests. It is demonstrated that sol id solution effect leads to a hardening effect whereas the presence vacancy leads to a softening effect. The electrical resistivity is shown to increase with vacancy content and substitution rate. Such an effect is discussed in terms of disorder and relaxation time variation. Finally, the anisotropic transport properties of MAX phases is studied and discussed. The anisotropy of transport properties has been evidenced by direct measurement of the resistivity along the basal plane and along the c-axis. It is demonstrated that transport property in the basal plane can be understood in the framework of a single band model with hole-like states as charge carrier.

La Côte Nord de l’Estuaire et du Golfe du St. Laurent (Québec, Canada) est caractérisée par une série de complexes deltaïques mis en place en contexte de chute de Niveau Marin Relatif (NMR) forcée par le rebond glacio-isostatique, lors du retrait des marges de l’Inlandsis Laurentidien. L’étude de trois complexes deltaïques montre qu’un motif d’évolution morphostratigraphique contrôlé par le retrait des marges glaciaires prévalait au premier ordre. Le premier stade de sédimentation se caractérise par la mise en place de cônes d’épandage juxtaglaciaires sous-aquatiques. Leur localisation au front de la marge glaciaire fait que la répartition spatiale des corps sédimentaires montre localement un empilement en rétrogradation. Dès l’émergence d’un front glaciaire continental, des deltas proglaciaires se développent en contexte de chute de NMR, formant des lobes dont l’altitude décroît vers le bassin. Ces derniers sont initialement associés à un système fluviatile en tresse alimenté en sédiments glaciogéniques par les marges glaciaires en retrait. Malgré des taux de chute de NMR de plusieurs cm/an, aucune incision fluviatile n’est observée à ce stade et la dynamique de transfert est prédominante du fait des forts taux d’apports sédimentaires. Plus tard, à la suite du retrait des marges glaciaires hors des bassins versants, le remaniement paraglaciaire se développe du fait de la réduction drastique des apports en eaux et sédiments. Le système fluviatile, devenu méandriforme, s’encaisse dans les anciens dépôts deltaïques maintenant inactifs et les bordures de deltas sont remaniées par les processus littoraux (plages soulevées, terrasses marines). Cette étude révèle que la majorité du volume de ces complexes deltaïques (10-20 km3) est mis en place en quelques milliers d’années seulement, immédiatement après la déglaciation ; le remaniement paraglaciaire n’ayant contribué à l’accrétion deltaïque que très marginalement. La modélisation numérique (Dionisos) valide les différents forçages identifiés par l’analyse morphosédimentaire. Une synthèse des complexes deltaïques à l’échelle de toute la Côte Nord du St. Laurent a permis de catégoriser 21 complexes deltaïques en 4 scénarios d’évolution morphosédimentaire, directement liés à la dynamique de retrait de la marge glaciaire. Leur décryptage offre une clef de lecture originale pour l’historique du retrait des marges glaciaires de l’Inlandsis Laurentidien sur la période 12-7.5 ka cal BP. / The North Shore of the St. Lawrence Estuary and Gulf is characterized by the presence of deltaic complexes that were emplaced under falling Relative Sea Level (RSL) forced by the glacio-isostatic rebound, immediately after the retreat of the Laurentide Ice Sheet (LIS) margin. The study of three deltaic complexes reveals that a common morphostratigraphic evolution forced by the retreat of the LIS prevailed for the edification of these structures, reflecting the retreat of the LIS margin. The emplacement of subaqueous outwash fans beyond the retreating or stillstanding glaciomarine margin constitutes the first stage of this evolution. As tied to the ice-margin position, these fans are characterized in places by a backstepping stacking pattern, in spite of the forced regressive setting. From the emergence of a continental ice front, the proglacial deltaic system develops and forms lobes staged accordingly to the RSL fall. These deltaic systems actively prograde at that time because they are fed in glaciogenics by the retreating LIS margin through braided meltwater streams. In spite of the RSL fall reaching several centimeters per years, no fluvial entrenchment occurs mainly owing to the significant amount of sediment supply. Later, when the LIS margin retreats from the drainage basins of feeding rivers, fluvial systems experience a drastic drop in sediment supply that forced the interruption of the deltaic progradation and the onset of paraglacial reworking. The paraglacial reworking consists in the entrenchment of a meandering fluvial system within former deltaic deposits and shows the prevalence of shallow-marine processes (waves, tides) at the delta rim (raised beaches, marine terraces). This study reveals that the bulk of the deltaic volume (c.a. 10-20 km3) for each complex was emplaced in only a few thousands of years following the LIS margin retreat when the latter was still located in the drainage basin. The paraglacial reworking had a minor influence on the deltaic accretion. A forward stratigraphic model (Dionisos) is used to validate the variety of forcing as understood from the sedimentary analysis. A synthesis including 21 deltaic complexes of the St. Lawrence North Shore allowed the establishment of a fourfold categorization. This scheme of deltaic evolution was used in order to refine the position of the LIS margin retreating upland for a period ranging from 12 to 7.5 ka cal BP.

Les propriétés spécifiques du titane en font un matériau de choix pour remplacer l’acier dans des applications où le poids est un paramètre de conception important. cependant, contrairement à l’acier, le titane souffre de mauvaises propriétés tribologiques. c’est pour répondre à cette problématique qu’il est envisagé de développer des composites à matrice métallique (cmm) titane renforcée par des particules de carbure de titane. dans le cadre de ce projet, plusieurs nuances de cmm à matrice ti ou ti-6al-4v contenants différentes fractions volumiques de particules de tic ont été élaborées par métallurgie des poudres. trois procédés ont été employés : le frittage libre, la compression isostatique à chaud et le filage. les différentes nuances ont ensuite été caractérisées du point de vue microstructurale (taux de densification, taille des grains) et mécanique (traction). la confrontation des résultats a permis d’établir un lien entre microstructure et propriétés mécaniques. dans l’optique d’étudier la mise en forme mais également d’améliorer les propriétés mécaniques, un post-traitement de type forgeage a été appliqué à la suite de la phase d’élaboration. excepté dans le cas des cmm filés, la présence de renforts entraîne l’apparition d’endommagement lors de la déformation à chaud. nous avons alors déterminé les conditions de forgeage les plus adaptées selon les nuances.finalement, à travers un travail de modélisation analytique et de simulation numérique par méthode d’homogénéisation, nous avons déterminé les grandeurs mécaniques (module de young et limite d’élasticité) et prévu la loi de comportement des cmm en traction. / The specific properties of titanium make it a key material for the replacement of steel in weight dependent applications. however, unlike steel, titanium suffers from poor wear resistance. in order to improve this weakness, it is proposed to develop titanium metal matrix composites (mmc) reinforced with titanium carbide particles.to this end, ti and ti-6al-4v mmc were prepared with reinforcement fractions ranging from 5 percent to 20 percent using three powder metallurgy techniques: free sintering, hot isostatic compression and extrusion. the composites were then characterized from a microstructural (density, grain size) and a mechanical (tensile test) point of view. by comparing the results, it was possible to establish a relationship between microstructural features and mechanical properties.following their preparation, the composites were subjected to a forging step in order to study their behavior during hot deformation and to further improve their mechanical properties. the presence of particles induces the apparition of damage during hot deformation. therefore, we determined the best forging for the different composites whilst taking microstructure into account.finally, through analytical modeling and numerical simulations, we determined the young modulus, the yield stress and predicted the behavior of a mmc during a tensile test.

L'objectif de ce travail de thèse consistait à développer d'une technologie de mise en forme de poudres d'aciers faiblement alliés nitrurées afin d'introduire le nitrure ε-Fe2-3N dans la masse de la pièce mécanique.Pour atteindre cet objectif, deux voies ont été étudiées :- réaliser des pièces frittées à partir de poudre d'acier nitrurée ou nitrurée-enrobée (contenant une teneur importante en nitrure ε),- nitrurer et densifier une poudre d'acier pendant l'étape de frittage.La nitruration d'une poudre d'acier 4140 lors du frittage en CIC s'est avérée insuffisante vis-à-vis des teneurs en nitrure ε nécessaires pour l'application industrielle.L'étude de la stabilité, en CIC, de la poudre d'acier 4140 nitrurée a démontré la conservation des nitrures γ' et ε en grande proportion jusqu'à des températures de 650°C, quel que soit la nature du cycle de CIC appliqué. L'étude de la stabilité, à 600°C, de poudres d'acier nitrurées placées en capsules scellées a montré une légère dénitruration de ces poudres pendant le traitement.Des essais de densification de ces poudres d'acier nitrurées ont ensuite été réalisés par frittage SPS puis CIC. Afin de densifier les particules d'acier nitrurées, nous avons choisi d'utiliser un liant. Les essais de frittage SPS ont permis de mettre en évidence les paramètres expérimentaux les plus pertinents pour l'obtention d'un matériau dense et comportant le nitrure ε, et de proposer des préconisations sur les compositions acier-liant. Ces compositions ont été testées en CIC avec succès. Deux d'entre elles ont ainsi permis l'obtention de matériaux denses aux propriétés tribologiques et mécaniques satisfaisantes pour l'application industrielle. / The aim of this Ph.D thesis was to develop a technology to shape nitrided low-alloyed steels powders to introduce the ε-Fe2-3N nitride in the volume of the mechanical component.To achieve this goal, two approaches were considered:- the sintering of coated nitrided steel powder or nitrided steel powder (containing a high content of ε nitride),- the simultaneous densification and nitriding of low-alloy steel powder during the sintering step.Nitriding 4140 steel powder during hot isostatic pressing (HIP) does not allow producing sufficient ε-phase content for industrial application.The stability study of nitrided 4140 steel powder during HIP shows that a huge proportion of nitrides (γ' and ε) is conserved at 650°C, regardless of the HIP cycle. The stability study, at 600°C, of nitrided steel powders placed in sealed evacuated glass tubes, shows a slight denitriding of these powders during the process.Thus, densification of these nitrided steel powders was made by spark plasma sintering (SPS) and HIP. To densify the nitrided steel particles, we have used a copper-phosphorous binder. From SPS experiments, we have deduced the most relevant experimental parameters to obtain a dense material containing ε-phase, and we have proposed recommendations on the composition of nitrided steel-binder mixture. The identified compositions were successfully sintered by HIP. Two of them allow obtaining dense materials with interesting tribological and mechanical properties for industrial application.

Im Rahmen der vorliegenden Arbeit wurden neuartige keramik- und stahlreiche Verbundwerkstoffe, auf Basis von MgO-teilstabilisiertem Zirkoniumdioxid und hochlegiertem austenitischem TRIP Stahl entwickelt. Die keramikreiche Verbundwerkstoffe mit bis zu 30 Vol.% metallischer Partikelverstärkung wurden über die Schlickergusstechnologie bzw. die Druckschlickergusstechnologie hergestellt und können als thermo-mechanisch beanspruchte Bauteile zum Einsatz kommen. Es wurden weiterhin metallreiche Verbundwerkstoffe mit bis zu 10 Vol.% keramischer Partikelverstärkung erstmalig über die Papiertechnologie hergestellt. Dadurch ergeben sich vielfältige Möglichkeiten metallreiche Leichtbaustrukturen mit verbesserten Energieabsorptionsvermögen zu erzeugen. Im Mittelpunkt der vorliegenden Arbeit stand die Entwicklung der keramikreichen Schlicker, die Formgebungstechnologien, die Entwicklung geeigneter Entbinderungs- und Sinterregime sowie die Charakterisierung der Verbundwerkstoffe hinsichtlich ihrer Mikrostruktur sowie der mechanischen bzw. der thermo-mechanischen Eigenschaften.