Made available in DSpace on 2014-10-09T12:51:30Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:02:10Z (GMT). No. of bitstreams: 1 11328.pdf: 13067508 bytes, checksum: 886d399df69a8146f0353092e99aa16a (MD5) / O objetivo deste trabalho foi desenvolver potenciais materiais para aplicações automotivas, em particular como insertos para assento de válvula em motores de combustão interna à gasolina. O desenvolvimento compreendeu as etapas de processamento dos materiais via metalurgia do pó, tratamento térmico, caracterização microestrutural e mecânica, usinagem e desgaste dos mesmos. O desenvolvimento objetivou principalmente a redução de custo e a aplicação de elementos menos poluentes, excluindo-se, por exemplo, a aplicação do Co devido ao seu alto custo e do Pb devido aos seus efeitos toxicológicos e prejudiciais ao meio ambiente. A realização de uma pesquisa minuciosa na busca de patentes relacionadas indicou que os materiais estudados apresentam composições particulares, e, portanto inéditas. Os resultados encontrados nos ensaios de dureza e de resistência à compressão radial nas amostras tratadas termicamente apresentaram resultados superiores aos da liga comercial atualmente em uso. Testes de usinabilidade em amostras sem tratamento térmico apresentaram comportamento similar ao da liga comercial, indicando que a usinabilidade do material praticamente não foi afetada com a mudança na composição química. Após a etapa de tratamento térmico, as ligas obtidas apresentaram valores de esforços de corte superiores aos do material comercial. Os resultados dos testes de desgaste abrasivo em amostras tratadas termicamente apresentaram menores valores de coeficientes de atrito e perda de massa em todos os casos em relação ao material comercial. Este comportamento é devido aos benefícios introduzidos pelo tratamento térmico executado e pela adição de alguns elementos resistentes ao desgaste na forma de carbonetos de Nb e Ti/W. Os resultados dos esforços de corte apresentaram boa concordância com os resultados dos ensaios de desgaste. Os materiais produzidos apresentam-se como potenciais candidatos para substituir, com vantagens, inserto para assento de válvula a base de Fe-Co em motores de combustão interna a gasolina. / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Submitted by Mery Piedad Zamudio Igami (mery@ipen.br) on 2017-03-10T16:23:34Z No. of bitstreams: 0 / Made available in DSpace on 2017-03-10T16:23:34Z (GMT). No. of bitstreams: 0 / Neste trabalho investigou-se a obtenção do composto TiFe a partir da moagem de alta energia de misturas de pós de TiH2 e Fe, seguida de aquecimento sob vácuo para a reação de síntese. No lugar do Ti, o TiH2 foi escolhido como precursor em razão de sua fragilidade, benéfica para a diminuição da aderência dos pós ao ferramental de moagem. Foram preparados dois lotes de misturas obedecendo-se a relação Ti:Fe de 50:50 e 56:44. Ambos foram processados em um moinho do tipo planetário por tempos que variaram de 5 até 40 horas, sob atmosfera de argônio de elevada pureza. Em todos os experimentos foram mantidos constantes a velocidade de rotação do prato do moinho, a quantidade de amostra, o diâmetro e o número de bolas. As amostras moídas foram caracterizadas por calorimetria exploratória diferencial (DSC), termogravimetria (TG), microscopia eletrônica de varredura (MEV), difração de raios X (DRX) e fluorescência de raios X por dispersão de energia (EDXRF). Apenas TiH2 e Fe foram observados nas amostras moídas, com um grau crescente de mistura em função do tempo de moagem. O composto TiFe nanoestruturado (12,5 a 21,4nm) foi obtido de forma majoritária em todas as amostras após a reação de síntese promovida pelo tratamento térmico a 600ºC (873K). As amostras reagidas foram caracterizadas por microscopia eletrônica de transmissão (MET) e DRX. Um equipamento do tipo Sievert, operando sob um fluxo constante (modo dinâmico), foi utilizado para levantar as curvas termodinâmicas de absorção e dessorção de hidrogênio. Todas as amostras absorveram hidrogênio à temperatura ambiente (~298K) sem a necessidade de ciclos térmicos de ativação. Os melhores resultados foram obtidos com as amostras moídas por 25 e 40 horas, de composição não estequiométrica 56:44. Tais amostras absorveram e dessorveram hidrogênio à temperatura ambiente, sob os platôs de aproximadamente 6,4 e 2,2bar (~0,6 e 0,2MPa), respectivamente. A capacidade máxima de armazenamento foi de 1,06% em massa de hidrogênio (H:M~0,546), sob pressão de até 11bar (1,1MPa), com reversão de até 1,085% em massa de hidrogênio (H:M~0,559), sob pressão de até 1bar (0,1MPa). Estas amostras também apresentaram maior cinética de absorção e dessorção de hidrogênio com fluxos de 1,23 (25h) e 2,86cm3/g.min. (40h). Tais resultados são atribuídos à variação composicional da fase TiFe e à maior quantidade de TiH2 livre. / Tese (Doutorado em Tecnologia Nuclear ) / IPEN/D / Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP

The pores in pressed and sintered components constitute weak points in the material since the stress concentration is larger than the nominal stress there. Therefore, fatigue cracks initiate at the pores. Specifically, it can be assumed that the fatigue cracks initiate at the largest pore in the stressed volume. Studies have previously looked at finding ways to model the fatigue strength of the material based on the largest pore. This thesis looks at a model previously derived for hardened pressed and sintered materials that is based on linear elastic fracture mechanics and investigates if said model can be modified to include non-hardened pressed and sintered materials that do not necessarily behave linear elastically. A model describing the influence of the size of the largest pore on the fatigue limit using empirical coefficients is suggested. Furthermore, the area of the largest pore is modelled using extreme value statistics. The model proved successful in modelling the density effect of the porosity on the fatigue strength for two materials with different microstructures: one with a homogeneous microstructure and one with a heterogeneous microstructure. For the material with the homogenoeous microstructure the model also accounted well for the notch effect when tested on samples with a different geometry. However, for the heterogeneous material the model did not account for the notch effect. Deformation hardening due to local plastic deformation in the softer phases was suggested as a possible explanation and was supported by tensile tests.

Bulk magnesium materials produced nowadays via powder metallurgy are based on a vastly extensive technological spectrum, which makes it possible to create a wide range of materials. This work focuses on the preparation of bulk materials from magnesium powder by cold pressing and hot pressing, sintering and field assisted sintering. The bulk materials were prepared in a series of compacting pressures from 100 MPa to 500 MPa and the sintering temperatures were selected in the range of 300 ° C to 600 ° C in order to characterize the influence of the manufacturing conditions and technology on the final properties of bulk materials. Prepared materials were evaluated in terms of microstructure, hardness, microhardness, three-point bend test, and fractography. From the hot pressed materials, the samples prepared at 400 and 500 MPa and 400 °C had the highest strength and hardness. The classic sintering of magnesium in the furnace with argon atmosphere proved to be ineffective due to the oxide layer on the surface and the presence of oxygen in technical argon. The SPS sintering (Spark Plasma Sintering) was the more effective with the lower applying pressure used to make the preforms and with the higher applied pressure during the SPS process itself. Highest strength and hardness were achieved in this case of materials sintered at 600 ° C prepared from free powder and the most porous preform (100 MPa). The bulk materials were prepared using all methods used, but the properties of these materials varied considerably depending on the technology used.

Vývoj nových materiálů pro součásti v moderních technologiích vystavené extrémním podmínkám má v současné době rostoucí význam. Děje se tak v důsledku neustále se zvyšujících požadavků průmyslových odvětví na lepší konstrukční vlastnosti nosných materiálů. Ve světle těchto faktů si tato studie klade za cíl posoudit nové složení slitin s vysokou entropií, které se vyznačují vysokým aplikačním potenciálem pro kritické aplikace. Slitiny jsou připravovány práškovou metalurgií, t.j. kombinací mechanického legování a slinování v pevné fázi. Pro účely srovnávaní vlastností jsou vybrané kompozice vyrobeny také tradičními metalurgickými metodami v roztaveném stavu, jako je vakuové indukční tavení a následné lití nebo vakuové obloukové tavení. Prášková metalurgie umožňuje postupný vývoj kompozitů s kovovou matricí (MMC) prostřednictvím přípravy oxidicky zpevněných HEA slitin. To je možné díky inherentním in-situ reakcím během procesu výroby. Když se naopak zvolí výrobní postup z taveniny, připravený kovový materiál vykazuje velké rozdíly v mikrostrukturách a souvisejících vlastnostech, v porovnání se stejným materiálem vyrobeným práškovou cestou (PM). Vyrobené práškové a tavené materiály jsou detailně charakterizovány s ohledem na komplexní vyhodnocení vlivu různých metod zpracování. Práce se zejména orientuje na mikrostrukturní charakteristiky materiálů a jejich mechanické vlastnosti, včetně vlivu tepelného zpracování na fázové transformaci a mikrostrukturní stabilitu připravených materiálů.

The present work deals with the comparison of the properties of metallic biomaterials in terms of their suitability for use as a temporary metal implant. In the work is judged biocompatibility of materials, they are comparing the corrosion rates and the influence of additives in the iron alloy to change biocompatibility and corrosion rate. In a part of this work is suggesting a method of preparing biodegradable metallic samples with different alloying elements and determine the methods, processes and measuring the corrosion rates. Part of this work is the chapter dealing with the function and effect of iron in the human body and any complications that may occur when a surplus caused by the release of part of the implant during its degradation or corrosion products. The outcome of this work is sort of created an iron-based samples in terms of their electrochemical corrosion potential, corrosion rate of samples exposed in various corrosive solutions, spectroscopic elemental analysis and outputs from the microscopic observation of the structures.

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.

This study presents results of selective laser melting (SLM), powder metallurgy (PM), and casting technologies applied for producing Ti–TiB composites from Ti–TiB₂ powder. Diffraction patterns and microstructural investigations reveal that chemical reaction occurred between Ti and TiB₂ during all the three processes, leading to the formation of Ti–TiB composites. The ultimate compressive strength of SLM-processed and cast samples are 1421 and 1434 MPa, respectively, whereas the ultimate compressive strengths of PM-processed 25%, 29%, and 36% porous samples are 510, 414, and 310 MPa, respectively. The Young’s moduli of porous composite samples are 70, 45, and 23 GPa for 25%, 29%, and 36% porosity levels, respectively, and are lower than those of SLM-processed (145 GPa) and cast (142 GPa) samples. Fracture analysis of the SLM-processed and cast samples shows shear fracture and microcracks across the samples, whereas failure of porous samples occurs due to porosities and weak bonds among particles.

Hochentropielegierungen stellen einen neuen Entwicklungsansatz metallischer Werkstoffe ohne ein eigenschaftsbestimmendes Hauptelement dar. Die zielgerichtete Übertragung der bisher überwiegend an Massivwerkstoffen ermittelten Eigenschaften in die Beschichtungstechnik erfordert die Kenntnis der bestimmenden Einflussfaktoren. Für die Schichtherstellung werden die Verfahren des thermischen Spritzens betrachtet. Hierfür wird eine geeignete Prozessroute ermittelt. Die detaillierten Untersuchungen zu den Prozess-Struktur-Eigenschaftsbeziehungen erfolgen an Legierungen mit variabler Struktur. Diese werden anhand von thermodynamischen Parametern sowie Untersuchungen an schmelzmetallurgisch hergestellten Massivwerkstoffen ausgewählt. Zur Bewertung des Einflusses der Größe der Strukturmerkmale, der Heterogenität und möglicher Ungleichgewichtszustände werden schmelz- und pulvermetallurgisch hergestellte Massivwerkstoffe als Referenz betrachtet. Die geplanten Forschungsarbeiten tragen zu einem Verständnis der Prozess-Struktur-Eigenschaftsbeziehung von Hochentropielegierungen bei. Weiterhin wird eine geeignete Prozessroute für die pulvermetallurgische Verarbeitung sowie für Anwendungen in der Oberflächentechnik ermittelt.

Ziel der Arbeit war es in einem pulvermetallurgischen Ansatz gasverdüste Ti-45Nb-Pulver mittels Heißpressen zunächst zu kompakten Formkörpern zu verpressen und über geeignete Gefügeeinstellung und bestmöglicher Partikelverzahnung maximale Druckfestigkeiten bei gleichzeitig niedrigem E-Modul zu erhalten. In einem nächsten Schritt wurden mittels Heißpressen mit Platzhalterphase definierte Porenanteile in die Formkörper eingebracht und der Einfluss dieser auf die mechanischen Eigenschaften untersucht. Die porösen Strukturen sollen als Knochenersatzmaterial in einem osteoporotischen Knochendefekt dienen. In einem solchen Defekt stellen Druckkräfte den dominierenden Belastungsfall dar. Die mechanische Charakterisierung der im Rahmen der Arbeit erzeugten porösen Formkörper erfolgte daher im Druckversuch. Die Oberfläche eines metallischen Knochenersatzmaterials muss chemisch und topografisch modifiziert werden, um damit Einfluss auf das Gleichgewicht zwischen zellbiologischen Prozessen zum Knochenauf- und -abbau an der Grenzfläche zwischen Implantat und Knochengewebe zu nehmen. Im speziellen Fall von Osteoporose, wo dieses Gleichgewicht nachweislich gestört ist, spielt die Stimulation des Knochenaufbaus eine besondere Rolle. Für Strontiumspezies konnte eine das Knochenwachstum stimulierende Wirkung und die Inhibierung des Knochenabbaus in mehreren Studien gezeigt werden. Ein weiteres Ziel der Arbeit stellte daher die Erzeugung von strontiumhaltigen Hydroxylapatitschichten mittels Elektrodeposition dar. Die erzeugten Schichten wurden strukturell, morphologisch und chemisch charakterisiert. Weiterhin wurden die Sr-Freisetzung aus den Schichten und die zellbiologische Wirkung untersucht. Konzepte zur Abscheidung auf planaren Legierungsoberflächen konnten in einem nächsten Schritt im Rahmen einer Machbarkeitsstudie auf poröse Ti-45Nb Strukturen übertragen werden. / Aim of the work was the production of dense Ti-45Nb material by hot-pressing of gas-atomized Ti-45Nb powder. Maximum compression strength and low Young’s modulus values were obtained by means of a tailored microstructure and improved interlinking of the powder particles. In a next step defined amounts of porosity were introduced by hot-pressing the alloy powder with a space holder phase. The produced porous structures should be used as bone substitute material in an osteoporotic bone defect. Compression is the dominating load in such a defect. Accordingly, compression tests were conducted to assess the mechanical properties. The surface state of metallic bone replacement materials plays an important role regarding the osseointegration of the material into the surrounding bone tissue. A chemical and topographical modification of the surface is necessary to influence the equilibrium between the formation and resorption of bone on the interphase of implant and bone tissue. Especially in case of osteoporosis the stimulation bone formation is essential. Several studies have shown that strontium species have a positive effect on the formation of bone tissue and the inhibition of bone resorption. Therefore, a further aim of the work was the electrodeposition of Sr-containing hydroxyapatite layers and the structural, morphological and chemical characterization of the deposited layers. Furthermore, the release of Sr-species from the layers and the effect on hMSC (human mesenchymal stroma cells) were examined. Originating from studies on planar alloy surfaces, the transfer of the deposition approaches was shown in a proof of concept on the porous Ti-45Nb scaffolds.