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.

Magnesium alloys have poor formability at room temperature, due to a limited number of slip systems owing to the hexagonal closed packed structure of magnesium. One possibility to increase the formability of magnesium alloys is to refine the grain size. A fine grain magnesium alloy shows high strength and high ductility at room temperature, hence an improved formability. In addition to grain refinement, the formability of Mg alloys can be improved by controlling crystallographic texture. Severe plastic deformation (SPD) processes namely, equal channel angular pressing (ECAP) and multi-axial forging (MAF) have led to improvement in room temperature mechanical property of magnesium alloys. Further, it has been reported that by adding rare earth elements, room temperature ductility is enhanced to nearly 30%. The increase in property is attributed to crystallographic texture. Many rare earth elements have been added to magnesium alloys and new alloy systems have been developed. Amongst these elements, Ce addition has been shown to enhance the tensile ductility in rolled sheets at room temperature by causing homogeneous deformation. It has been observed that processing of rare-earth containing alloys below 300°C is difficult. Processing at higher temperatures leads to grain growth which ultimately leads to low strength at room temperature. The present thesis is an attempt to combine the effect SPD and rare earth addition, and to examine the overall effect on microstructure and texture, hence on room temperature mechanical properties. In this thesis, Mg-0.2%Ce alloy has been studied with regard to the two SPD processes, namely, ECAP and MAF. The thesis has been divided into six chapters. Chapter 1 is dedicated to introduction and literature review pertaining to different severe plastic deformation processes as applied to different Mg alloys. Chapter 2 includes the details of experimental techniques and characterization procedures, which are commonly employed for the entire work. Chapter 3 addresses the effect of ECAP on the evolution of texture and microstructure in Mg-0.2%Ce alloy. ECAP has been carried out on two different initial microstructure and texture in the starting condition, namely forged and extruded. ECAP has been successfully carried out for the forged billets at 250°C while cracks get developed in the extruded billet when ECAP was done at 250°C. The difference in the deformation behaviour of the two alloys has been explained on the basis of the crystallographic texture of the initial materials. The microstructure of the ECAP materials indicates the occurrence of recrystallization. The recrystallization mechanism is identified as “continuous dynamic recovery and recrystallization” (CDRR) and is characterized by a rotation of the deformed grains by ~30⁰ along c-axis. The yield strengths and ductility of the two ECAP materials have been found quite close. However, there is a difference in the yield strength as well as ductility values when the materials were tested under compression. The extruded billet has the tension compression asymmetry ~1.7 while the forged material has the asymmetry as ~2.2. After ECAP, the yield asymmetry reduces to ~1 for initially extruded billet, while for the initially forged billet the yield asymmetry value reduces to ~1.9. In chapter 4, the evolution of microstructure and texture was examined using another severe plastic deformation technique, namely multi axial forging (MAF). In this process, the material was plastically deformed by plane strain compression subsequently along all three axes. In this case also two different initial microstructures and texture were studied, namely the material in as cast condition and the extruded material. The choice of initial materials in this case was done in order to examine the effect of different initial grain size in addition to different textures. By this method, the alloy Mg-0.2%Ce could be deformed without fracture at a minimum temperature of 350⁰C leading to fine grain size (~3.5 µm) and a weak texture. Grain refinement was more in the initial cast billets compared to the initial extruded billet after processing. The mechanism of grain refinement has been identified as twin assisted dynamic recrystallization (TDRX) and CDRR type. The mechanical properties under tension as well as under compression were also evaluated in the present case. The initially extruded billet has shown low tension compression asymmetry (~1.2) than cast billet (~1.9), after MAF. Chapter 5 addresses the exclusive effect of texture on room temperature tensile properties of the alloy. Different textures were the outcomes of ECAP and MAF processes. In this case, in order to obtain an exact role of texture, a third of deformation mode, rolling, was also introduced. All the processed materials were annealed to obtain similar grain size but different texture. A similar strength and ductility for ECAP and MAF, where the textures were qualitatively very different, was attributed to the fact that texture of both the ECAP and MAF processed materials, was away from the ideal end orientation for tensile tests. In chapter 7, the final outcomes of the thesis have been summarized and scope for the future work has been presented.

The presented diploma thesis deals with the modeling of the rotor packet in dynamic calculations and analysis of the influence of the packing pressing force on the critical speed of the electric motor. The thesis can be divided into three main parts. The first part discusses the current level of rotor packet modeling in dynamic calculations and also deals with analytical theories for subsequent experimental tests. The second part describes the implementation of two experiments to determine the equivalent modulus of elasticity. The first experiment is a four-point bending test and the second is an experimental modal analysis. The third part is used for comparing the results obtained from experimental tests and describes the calculation of the critical speed of the rotor package pressed on the shaft by the finite element method.

JURČA Jan: The manufacturing of sheet metal part by deep draw technology. Thesis of Master´s Studies, the 5th Year of Study, the School-year 2008/2009, The Institute of Manufacturing Technology, Department of Machining, FSI VUT Brno.The thesis deals with the project of manufacturing the part of the car body – the fifth door by deep draw technology. The material is zinc-coated sheet metal HX220YD EN 10292. Mechanical properties and suitability of the material are evaluated by mechanical tests. The structure of the material is evaluated by metalography scratch pattern. The analysis of draw process and manufacturability of the part is made by calculations and AutoForm software. The production line, necessary machinery and construction solution of draw tool for the manufacturing the part are determined. Last section deals with economical evaluation of the production.

The thesis compares oxidation and fusion laser cutting methods in the production of sheet components called Trager consoles. Individual methods of laser cutting are compared in terms of achieved quality and properties of cutting areas. Consequently, the effect of these properties on consecutive technological operations, which are mainly threading and pressing the nuts into components, are evaluated. In the experimental part of the thesis the roughness of cut surfaces was measured and the cuts were classified into quality classes according to the ČSN EN ISO 9013 standard. Metallographic samples were taken in order to measure hardness and determine its course in the direction from the cutting edge into the material. The metallographic samples were further used for capturing detailed images on the microscope and assessing the quality of nuts pressing. Afterwards, the cut moments affecting taps were measured in order to verify the impact of cutting edge properties on threading. These measurements provided sufficient data for comparing the influence of cutting edge properties in individual methods of laser cutting on consecutive operations. Finally, individual methods were compared in terms of production costs. According to all the data and the conclusions reached, fusion method was identified as the most suitable method of laser cutting for components manufacturing.

This thesis deals with complex analysis of fine-grained magnesium alloy AZ91 prepared by ECAP process. Mechanical properties of investigated alloy in different states at various external conditions are compared. The structure of this material is inherently unstable therefore changes on microstructural and sub-microstructural level occur during thermal exposure and/or mechanical loading. These changes are analysed and quantified for investigated alloy in selected states in this thesis.

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.

Aufgrund ihrer herausragenden Eigenschaften haben ultrafeinkörnige Werkstoffe, die aus konventionellen normalkörnigen Halbzeugen über eine extrem große Kaltverformung hergestellt wurden, in den letzten zwei Jahrzehnten zunehmend an Bedeutung erlangt. In der vorliegenden Arbeit wird das Fließspannungsverhalten eines Reinaluminiumwerkstoffes (EN AW-1070 – Al99,7) und einer ausscheidungshärtbaren Aluminiumlegierung (EN AW-6060 – AlMgSi) mit Korngrößen von bis zu 660 nm und 310 nm in einem weiten Bereich von Dehnungen und Dehnraten analysiert und mit den zzt. existierenden Modellvorstellungen zu den mikrostrukturellen Abläufen in Verbindung gebracht. Um die Voraussetzung zur Herstellung von ultrafeinkörnigen Werkstoffen zu schaffen, wurden mehrere Werkzeugprototypen für die ECAP-Umformung im Labormaßstab entwickelt und erprobt. Die Untersuchungen zum Fließspannungsverhalten erfolgten anhand von Zug- und Druckversuchen über insgesamt sieben Dekaden der Dehnrate bis in den Bereich der hochdynamischen Belastung von 10^3 s^-1. Die Tests zeigen, dass das Fließspannungsverhalten ultrafeinkörniger Aluminiumwerkstoffe vollständig mithilfe der thermisch aktivierbaren Mechanismen erklärbar ist, wobei Ausscheidungen eine wichtige Rolle spielen. / Because of their exceptional properties ultrafine-grained materials, processed from conventional polycrystalline materials by severe plastic deformation, have gained increasing scientific and industrial interest during the last two decades. Based on the concept of work-hardening for f.c.c. metals the commercially pure aluminium AA1070 (Al99,7 – soft annealed) and the aluminium alloy AA6060 (AlMgSi – peak aged) were investigated. ECAP was used to introduce very high strains and an ultrafine-grained microstructure with grain sizes down to 660 nm and 310 nm. Subsequently compression and tensile tests were performed in a wide range of strain rates over seven decades up to the range of impact loading of 10^3 s^-1. The results indicate that strain path and the corresponding dislocation structure is important for the post-ECAP yielding and the following hardening response. Furthermore the precipitates of the AA6060 clearly constrain the interactions of dislocations in work-hardening stage III – causing lower strain rate sensitivity. If compared to the AA1070 they avoid hardening in stage V where an additional rate and temperature depending effect contributes – caused by the interaction of deformation induced vacancies and dislocations. The results indicate that the strain-hardening behavior can be described by thermal activated mechanisms.

1. Beim feldaktivierten Sintern im Temperaturbereich von 500 bis 1000 °C fließen elektrische Ströme mit einer Dichte von 1 bis 3 A/mm². 2. Daraus folgt für die größten verwendeten Pulverteilchen mit einem Radius von 50 µm ein Strom je Teilchenkontakt von 10 bis 50 mA. 3. Die durch das Aufbringen des prozesstechnisch notwendigen Pressdruckes gebildeten relativen Kontaktradien (Kontaktradius geteilt durch Teilchenradius) haben eine Größe von 0,05 bis 0,3. 4. Die Einengung der Strompfade im Kontakt der Pulverteilchen erhöht, zusammen mit dem elektrischen Widerstand der Oxidschicht auf den Pulverteilchen, den elektrischen Widerstand des Pulverpresslings. 5. Der Stromfluss durch die Teilchenkontakte führt mit dem zusätzlichen elektrischen Widerstand dieser Teilchenkontakte zu einer lokalen Temperaturerhöhung (Übertemperatur) von 10-4 bis 1 Kelvin für Kupfer- respektive Stahlpulver. 6. Der zusätzliche elektrische Widerstand der Oxidschicht kann die Übertemperatur beim Kupferpulver auf bis zu 1 mK erhöhen. 7. Mit abnehmendem Teilchenradius sinkt die Übertemperatur quadratisch. 8. Das Wachstum der Teilchenkontakte im Verlauf der Verdichtung führt zu einer kontinuierlichen Verringerung der Übertemperatur. 9. Das Auftreten von schmelzflüssiger Phase, von Metalldampf oder von Plasma wird in den untersuchten metallischen Systemen ausgeschlossen. 10. Auch Elektromigration, Thermomigration oder andere Wirkungen des elektrischen Stromes spielen keine Rolle für die Verdichtung beim feldaktivierten Sintern. 11. Die Verwendung von gepulstem anstelle von kontinuierlichem Gleichstrom beeinflusst die Verdichtung der untersuchten Werkstoffe nicht. 12. Die Verdichtung vom Pulver zum kompakten Werkstoff findet für Pulverteilchen mit einem Radius größer als R = 10 µm über plastische Verformung durch verschiedene Formen des Kriechens statt. 13. Die Verformung ist im Anfangsstadium auf den Kontaktbereich begrenzt. 14. Bei Pulverteilen mit Teilchenradien unter R = 10 µm findet die Verdichtung zunächst als Folge von Leerstellenströmen in die Kontaktkorngrenze statt (Sintern). 15. Durch die schnelle Verdichtung bei niedriger homologer Temperatur werden Kornwachstum und Rekristallisation verringert.

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.