Ce travail s'inscrit dans le cadre du développement de matériaux composites nanostructurés à propriétés électriques et magnétiques inédites. Afin de répondre à des besoins technologiques pour, l'électronique de puissance intégrée : le stockage ou la transmission de l'énergie, les télécommunications (antenne intégrée...), le stockage de l'information par enregistrement magnétique et le marquage biologique, le composite doit présenter globalement une polarisation magnétique élevée ainsi qu'un comportement isolant permettant de pousser les limites fréquentielles, minimiser les pertes dynamiques et découpler les grains entre eux. Les matériaux composites élaborés sont constitués d'une matrice d'accueil - magnétique (ferrite spinelle) ou non-magnétique (diélectrique = silice) - dans laquelle sont dispersées des particules métalliques (Fer-Nickel ou Cobalt). Ces matériaux sont novateurs dans la mesure où le matériau final peut bénéficier d'un couplage des propriétés magnétiques des deux phases constitutives. L'holographie électronique en transmission a mis en évidence une ocnfiguration de spins de type « vortex » dans les nanoparticules de Fe30Ni70. Les mesures holographiques ont été comparées au profil de l'aimantation, dans un vortex, modélisé par une approche micromagnétique. Des analyses physico-chimiques approfondies nous ont permis de confirmer les topologies visées : pour le composite métal-diélectrique, l'épaisseur de la couche d'enrobage a pu être contrôlée à l'échelle nanonométrique. Pour le composite métal-oxyde obtenu par croissance directe du ferrite sur la phase métallique, on a démontré une bonne dispersion des particules métalliques. Les propriétés magnétiques et structurales des différents composites, en poudre ou compactés par SPS (compactage-frittage flash), ont été caractérisées et discutées. Les propriétés fonctionnelles ont été aussi étudiées et sont très prometteuses pour les applications visées. L'enrobage des nanoparticules par la silice a permis la préparation de leur surface dans la perspective d'une fonctionnalisation par des entités biologiques.

In the modern practice, a sustainable development strategy in a domain of wasteutilization is shifting its focus from a general completeness of recycling to a morespecific attention to efficiently utilize elements in the wastes. This is well-illustrated bythe steelmaking slag industries. The major waste product from the steelmaking practiceis slag and its main constituents are: CaO, SiO2, Al2O3, MnO, FeO and so on. The mainfield of application for the steelmaking slags is civil engineering, especially for road andwaterway construction. However, a significant amount of the slag remains in the dumps,damaging the environment as well as requiring a land for secure storage. Efficientrecycling of these materials is of increasing interest worldwide as a result of increasingsustainability in processes with respect to increasing raw material costs and wastereduction.In order to find a practical solution, joint efforts are currently made at the RoyalInstitute of Technology, Sweden and National Metallurgical Academy of Ukraine. Theconcept is based on transformation of non-magnetic wüstite (FeO) to magneticmagnetite (Fe3O4) using an oxidizing atmosphere was proposed.In order to verify the feasibility of the proposed way of slag utilization, experiments onthe ternary CaO-FeO-SiO2 and quaternary CaO-FeO-SiO2-MnO slags systems,accompanied by thermodynamic and kinetic modelling, were performed. The crystalprecipitation during synthetic slag oxidation was observed by Confocal Scanning LaserMicroscopy (CSLM). Precipitated phases were found to be magnetite and manganeseferrite in the spinel form.Obtained magnetite and manganese ferrite can be separated from the slag by magneticseparation.The formation of nanosize manganese ferrite from the CaO-FeO-SiO2-MnO slag systemduring oxidation was investigated. Experiments were conducted in a horizontalresistance furnace in an oxidizing atmosphere (air). The final product was analysed by Xraydiffraction (XRD). The particles size of the manganese ferrite was estimated by theScherrer formula and was found to be of the order of 23-25 nm. In order to get anunderstanding of the magnetic properties of the manganese ferrite recovered from slagtreatment, it was necessary to synthesize a reference compound from pure precursors.The MnFe2O4 nanopowder was synthesized by the oxalate route. The size effects on themagnetic properties of manganese ferrite particles were investigated.IIThe potential way of the magnetite particles separation from liquid slags was investigatedby cold model studies. The experimental technique of mobilising non-conducting,nonmagnetic particles in conducting liquid in crossed electric and magnetic fields wasinvestigated in order to find the way of the particle separation from the liquidsteelmaking slags. The effects of the current density, magnetic field, size and shape ofthe particle on the particle velocity under action of the electromagnetic buoyancy force(EBF) in the electrolyte were analyzed. / QC 20100916

Die Arbeit widmet sich dem Fließverhalten von Stählen bei zyklisch inkrementeller Torsion. Dazu werden vergleichend Reineisen und der ferritisch-perlitische Stahl 42CrMo4N bei unterschiedlichen Verformungspfaden betrachtet. Vor allem in zyklischen Torsionsversuchen mit bleibendem Verformungsinkrement je Zyklus werden Fließkurvenverläufe und Verformungsverfestigung analysiert. Die Ergebnisse belegen den Einfluss des lamellaren Zementit auf das Fließverhalten des Stahls 42CrMo4N, während die Eigenschaften des Reineisens von der entstehenden Versetzungszellstruktur bestimmt werden. Die Richtungsabhängigkeit der Fließspannung und die Verläufe der Fließkurven unterscheiden sich für die betrachteten Werkstoffe deutlich. Fließortkurven dienen der quantitativen Beschreibung der Verfestigung. Die Vorgehensweise zu ihrer Ermittlung und ihre Abhängigkeit von den Versuchsbedingungen und den Verformungszuständen werden gezeigt. Bei Reineisen dominieren isotrope, bei dem Stahl 42CrMo4N kinematische Verfestigungsanteile das Fließverhalten. / Ferritic-pearlitic steel 42CrMo4N and pure iron under different strain paths are compared regarding their flow behaviour. Mainly in cyclic torsion tests with resulting strain increment per cycle shear stresses and strain hardening are analysed. The results show, that the cementite lamellae determine the flow behaviour of the steel 42CrMo4N, whereas the properties of pure iron are governed by the evolving dislocation cell structure. The dependency of flow stress on the strain direction is different for the two materials. Yield surfaces describe strain hardening quantitatively. The procedure for yield point detection and the dependency of subsequent yield surfaces on experimental conditions and strain states is shown. For pure iron isotropic hardening, for steel 42CrMo4N kinematic strain hardening dominates the flow behaviour.

Actuellement, l’industrie automobile est à la recherche d’une meilleure solution pour l’allégement de la structure de véhicule afin de diminuer la consommation de carburant et par conséquent diminuer les émissions nocives de CO2. Les aciers à très haute résistance (THR) mécanique permettent d’obtenir les tôles d’acier à section diminué avec les mêmes ou meilleurs propriétés fonctionnels. Les aciers Dual-Phase (DP), constitués majoritairement d’une phase ductile, la ferrite, et d’une phase dure, la martensite, occupent une place importante en tant que matériaux de structure destinés au challenge préoccupant l’industrie automobile. Une bonne résistance à l’endommagement est exigée pour leur utilisation en tant que des pièces de structures et de renfort pour l’automobile. Il a été bien établi que la résistance à l’endommagement des ces aciers Dual-Phase est contrôlée par leur microstructure. Ce travail de thèse s’est inscrit dans une logique de compréhension des mécanismes d’endommagement d’un acier Dual-Phase modèle, le DP 780, en fonction de différents paramètres microstructuraux. Deux mécanismes d’endommagement ont été identifiés pour l’acier DP 780 : la décohésion de l’interface ferrite/martensite et la formation de cavités autour des carbures, dans la martensite revenue. Un modèle qualitatif de mécanisme d’endommagement a été développé afin de pouvoir prédire l’endommagement de l’acier DP 780. Ce modèle qualitatif, développé pour l’acier DP 780, servira de base d’approfondissement de modèles plus élaborés et quantitatifs permettant la compréhension et la prédiction de l’endommagement des aciers Dual-Phase, de façon générale / In the automotive industry current environmental concerns require that the vehicle fuel consumption and CO2 emissions should be reduced as much as possible. It is therefore advantageous to reduce the weight of body in white components by replacing existing parts with higher strength, thinner gauge alternatives with equivalent or improved functional properties. Dual Phase (DP) steels are a class of high-strength low-alloy steels characterized by a microstructure consisting of martensite and ferrite. Dual Phase steels combine high strength levels with good ductility. Thus, DP steels are potentially very attractive for the automobile industry. In addition to the required high strength and ductility, DP steel has to be cold formed into complex shapes. It appears that DP steel damage behaviour is very complex and cannot be predicted using existing models based on standard mechanical properties. This work is concerned with the study of microstructural evolution and investigation of the relation between the microstructure and damage mechanisms in a reference DP 780 steel. Two damage mechanisms have been identified in this DP steel: ferrite/martensite interface decohesion and void formation at tempered carbides. A simple modeling for qualitative description of the observed damage formation mechanisms is proposed. This modeling permits a basic understanding of the experimentally observed trends and could be used as the starting point for a more detailed analysis in future

V dnešní době je kladen vysoký nárok na účinnost elektrických zařízení a to jak ze strany provozovatele, tak i legislativy. Nejlepší účinnosti dosahují synchronní motory s permanentními magnety umístěnými na povrchu rotoru (SMPM), se kterými lze i u malých motorů dosáhnout účinnosti nad 90%. Nicméně tyto motory jsou z důvodů použití magnetů ze vzácných zemin, např. NdFeB, drahé a jsou schopny provozu pouze s frekvenčním měničem. Z cenových důvodů jsou hledány levnější alternativy k SMPM motorům. Jedním z typů motorů, kterým lze SMPM nahradit je synchronní reluktanční motor s permanentními magnety (PMASR). Tento motor je cenově výhodnější, protože používá menší množství magnetů, při zachování podobných, mnohdy i lepších vlastností, nicméně neodpadá potřeba použití frekvenčního měniče. Navíc je zde možnost použití levnějších feritových magnetů a tím ještě výrazněji snížit cenu motoru. V této práci bude PMASR topologie popsána důkladněji včetně elektromagnetického návrhu metodou konečných prvků. Bude provedena i mechanická analýza zvoleného optimálního modelu. Výsledky dosažené metodou konečných prvků budou následně porovnány s analytickým modelem. Z navrženého modelu bude vyroben prototyp a naměřené výsledky budou porovnány s výpočty.

The thesis deals with the influence of free various technological grinding processes of pure clinker minerals. The goals is to synthetically prepare pure clinker minerals and monitor the effect of the duration of the grinding process and monitor the impact of grinding technology on their crystallinity. A laser granulometry and XRD analysis are used for evaluation.

Die Arbeit widmet sich dem Fließverhalten von Stählen bei zyklisch inkrementeller Torsion. Dazu werden vergleichend Reineisen und der ferritisch-perlitische Stahl 42CrMo4N bei unterschiedlichen Verformungspfaden betrachtet. Vor allem in zyklischen Torsionsversuchen mit bleibendem Verformungsinkrement je Zyklus werden Fließkurvenverläufe und Verformungsverfestigung analysiert. Die Ergebnisse belegen den Einfluss des lamellaren Zementit auf das Fließverhalten des Stahls 42CrMo4N, während die Eigenschaften des Reineisens von der entstehenden Versetzungszellstruktur bestimmt werden. Die Richtungsabhängigkeit der Fließspannung und die Verläufe der Fließkurven unterscheiden sich für die betrachteten Werkstoffe deutlich. Fließortkurven dienen der quantitativen Beschreibung der Verfestigung. Die Vorgehensweise zu ihrer Ermittlung und ihre Abhängigkeit von den Versuchsbedingungen und den Verformungszuständen werden gezeigt. Bei Reineisen dominieren isotrope, bei dem Stahl 42CrMo4N kinematische Verfestigungsanteile das Fließverhalten. / Ferritic-pearlitic steel 42CrMo4N and pure iron under different strain paths are compared regarding their flow behaviour. Mainly in cyclic torsion tests with resulting strain increment per cycle shear stresses and strain hardening are analysed. The results show, that the cementite lamellae determine the flow behaviour of the steel 42CrMo4N, whereas the properties of pure iron are governed by the evolving dislocation cell structure. The dependency of flow stress on the strain direction is different for the two materials. Yield surfaces describe strain hardening quantitatively. The procedure for yield point detection and the dependency of subsequent yield surfaces on experimental conditions and strain states is shown. For pure iron isotropic hardening, for steel 42CrMo4N kinematic strain hardening dominates the flow behaviour.

Методом ориентационной микроскопии (EBSD) исследованы структурно-текстурные состояния бесшовных труб из сталей 08ХМФЧА, 25ХМФБ,10Х13Н3МФБ, после горячей прокатки и термических обработок. Установлено, что все структуры (феррит, бейнит, мартенсит) в изделиях как после горячей деформации, так и после термических обработок, характеризуются наличием выраженной кристаллографической текстуры, которую наиболее точно можно определить, как аксиальную, ось которой <111> является параллельной касательной к диаметру трубы. Показано, что процесс формирования текстуры также, как и наблюдающаяся в процессе термической обработки текстурная наследственность, определяются следующими правилами отбора определенных ориентаций α-фазы при γ-α-превращении: 1) наличием стабильных деформационных ориентировок аустенитных зерен; 2) специальными разориентациями (границами) между зернами γ–фазы, на которых начинается превращение; 3) ориентационными соотношениями, реализующимися при превращении; 4) термическими напряжениями, возникающими в изделии при его охлаждении. Последние являются ответственными за формирование специфической кристаллографической текстуры γ-α-превращения в бесшовных стальных трубах. / Microstructure and texture in seamless 0.08C–Cr–Mo–V; 0.25C–Cr–Mo–V–Nb; 0.08–13Cr–3Ni–Mo–V–Nb steel pipes were studied in as rolled and heat treated states using orientation EBSD microscopy. It was found that all types of microstructure (ferrite, martensite, bainite) as well as after hot rolling and after heat treatment have well defined axial crystallographic texture where <111> direction is predominately perpendicular to pipe surface. It was shown that texture formation in heat treated states is inherited due to following factors important for rules of orientation selection during γ to α phase transformation: 1) occurrence of stable orientation of austenite grains resulted from straining; 2) special misorientation (boundaries) of austenite grains where transformation starts; 3) orientation relationships known for phase transformation; 4) thermal stresses in product formed during cooling. The last can be considered as factor defining special texture in steel seamless pipes.

В работе проведен обзор основных технологий производства холоднокатаных листов низкоуглеродистых сталей для изготовления изделий методом холодной штамповки и эмалирования. Проанализированы химические составы, структура, кристаллографическая текстура образцов листов, и их влияние на возможности производства бытовых изделий (ванн, моек, поддонов). Рассмотрены вопросы улучшения качества листов низкоуглеродистых сталей, используемых для холодной штамповки и эмалирования. / The paper reviews the main technologies to produce cold-rolled sheets of low-carbon steels for the manufacture of products by cold stamping and enameling. The chemical compositions, structure, crystallographic texture of sheet samples, and their influence on the possibility of manufacturing household products (bathtubs, sinks, and pallets) are analyzed. The issues of improving the quality of low-carbon steel sheets used for cold stamping and enameling are considered.

This master thesis presents a theoretical investigation of the energy and stability of interfaces in iron-carbide compounds, specifically focusing on the α-Fe/Cr7C3 system. The study aims to fill the gap in knowledge regarding the surface energetics of these interfaces using Density Functional Theory (DFT). Six different α-Fe/Cr7C3 interfaceswere constructed α-Fe(001)/Cr7C3(024), α-Fe(001)/Cr7C3(202), α-Fe(001)/Cr7C3(040),α-Fe(110)/Cr7C3(024), α-Fe(110)/Cr7C3(202) and α-Fe(110)/Cr7C3(040). Due to limited computational resources, only one of them was computationally analyzed to determine its interfacial energy value. The results revealed that the interfacial energy of the α-Fe(001)/Cr7C3(040) interface falls within the range of incoherent interfaces, indicating its stability. The computed interfacial energy values ranged from 0.94 to 3.39 J/m2, consistent with similar studies on other iron interfaces. The simulations also identified minimum and local minimum points in the interface energy curve, representing stable configurations at specific interface separation distances. The presence of a minimum point at an interface separation value of d = 1.3551 Å with an interfacial energy of 0.94 J/m2 indicates the most stable configuration, while a local minimum point at d = 2.27 Å with an interfacial energy of 2.12 J/m2 suggests another stable configuration for the interface. The conclusion that the computations were correctly performed with an interfacial energy value of 0.94 J/m2 for the most stable configuration at a supercell length (aSupercell ) of 22.23 Å is drawn. The findings of this research have significant implications for future investigations and applications. Firstly, this study fills the gap of the unresearched ferrite-carbide interfaces with theoretical data. Secondly, the knowledge gained from studying these interfaces contributes to understanding hydrogen interactions, which is fundamental for the transition towards a hydrogen economy. Additionally, the incoherent nature of the interface introduces challenges in understanding material behavior and properties, necessitating further investigations for designing efficient systems. Future work includes experimental validation of the α-Fe/Cr7C3 interface to compare the theoretical and experimental energies and stability. Investigating the remaining interfaces and examining the effects of introducing hydrogen atoms in these interfaces, along with calculating the corresponding hydrogen trapping energies, are important research areas. Further advancements in understanding these interfaces can be achieved through interface engineering, multiscale modeling, and studying other iron-carbide systems. / Detta examensarbete presenterar en teoretisk undersökning av energin och stabiliteten hos gränssnitt i järnkarbidföreningar och fokuserar specifikt på α-Fe/Cr7C3-systemet. Studien syftar till att fylla kunskaps tomrummet gällande ytegenskaperna hos dessa gränssnitt genom användning av densitetsfunktionalteori (DFT). Sex olika α-Fe/Cr7C3-gränssnitt konstruerades α-Fe(001)/Cr7C3(024), α-Fe(001)/Cr7C3(202), α-Fe(001)/Cr7C3(040), α-Fe(110)/Cr7C3(024), α-Fe(110)/Cr7C3(202) och α-Fe(110)/Cr7C3(040). På grund av begränsade beräkningsresurser analyserades endast ett av dem för att bestämma dess gränssnittsenergivärde. Resultaten visade att gränssnittsenergin för α-Fe(001)/Cr7C3(040)- gränssnittet ligger inom intervallet för inkoherenta gränssnitt, vilket indikerar dess stabilitet. De beräknade gränssnittsenergivärdena varierade mellan 0,94 och 3,39 J/m2 , vilket är i linje med liknande studier där järngränssnitt studeras. Minimi och lokala minimipunkter i gränssnittets energikurva, vilket representerar stabila konfigurationer vid specifika avstånd mellan gränssnittet. Förekomsten av en minimipunkt vid ett gränssnittsavstånd på d = 1,35 Å med en gränssnittsenergi på 0,94 J/m2 indikerar den mest stabila konfigurationen, medan en lokal minimipunkt vid d = 2,27 Å med en gränssnittsenergi på 2,12 J/m2 antyder en annan stabil konfiguration för gränssnittet. Slutsatsen dras att beräkningarna utfördes korrekt med ett gränssnittsenergivärde på 0,94 J/m2 för den mest stabila konfigurationen vid en supercellslängd (aSupercell) på 22,23 Å. Fynden från denna forskning har betydande implikationer för framtida undersökningar och tillämpningar. För det första fyller denna studie kunskapsgapet gällande de otillräckligt utforskade ferrit-karbidgränssnitten med teoretisk data. För det andra bidrar den erhållna kunskapen från studiet av dessa gränssnitt till förståelsen av väteinteraktioner, vilket är grundläggande för övergången till en väteekonomi. Dessutom innebär gränssnittets inkoherenta natur utmaningar när det gäller att förstå materialbeteende och egenskaper, vilket kräver ytterligare undersökningar för att utforma effektiva system. Framtida arbete inkluderar experimentell validering av gränssnittet mellan α-Fe/Cr7C3 för att jämföra teoretiska och experimentella energier och stabilitet. Att undersöka återstående gränssnitt och undersöka effekterna av att introducera väteatomer i dessa gränssnitt och beräkna motsvarande vätefällningsenergier är viktiga forskningsområden. Gränssnittsdesign, flerskalig modellering och studier av andra järnkarbid-system kan ytterligare främja förståelsen av dessa gränssnitt.