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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
101

Elaboration et caractérisation de composés hydrurables types AB3 (A : terre rares, B : métal 3d) pour le stockage et la conversion d'hydrogène / Elaboration and characterization of AB3 type intermetallic compounds (A : Rare earth, B : transition metal) for hydrogen storage and conversion

Chebab, Safa 07 February 2017 (has links)
La demande en énergie ne cesse d'augmenter et elle satisfaite essentiellement par les énergies fossiles qui présentent une contrainte environnementale vue ses émissions de gaz à effet de serre. Considéré comme vecteur énergétique, l'hydrogène possède l'immense avantage de ne pas émettre de gaz à effet de serre et notamment du CO2. Son stockage dans des intermétalliques permet d’obtenir des capacités massiques et volumiques supérieures à celles obtenues en voie liquide ou sous pression. Dans ce travail, nous avons élaboré le composé intermétallique quaternaire LaCaMgNi9 par mécanosynthèse et ce selon différents schémas réactionnels. Ce procédés de synthèse est employé pour la première fois, pour la synthèse de cet intermétallique, afin de s'affranchir des difficultés que présentent les autres techniques de synthèse (co-fusion, frittage). Les caractérisations structurales et morphologiques des alliages obtenus ont été réalisées afin de tester leurs performances en tant que matériaux pour électrode négative d’accumulateur Ni-MH par divers techniques de caractérisation électrochimiques et solide-gaz / The increasing energy demand is mainly supplied by fossil sources which had environmental drawback essentially greenhouse gas emission. Considered as an energy carrier, hydrogen has the huge advantage to be clean. Its storage in intermetallic compound leads too higher hydration capacities than liquid and compressed storage. In this work, LaCaMgNi9 quaternary type alloy has been synthesized, for the first time, by mechanical alloying in order to avoid the inherent difficulties of the fusion technique. The structural and morphological characterization of the obtained alloys were performed. Their hydrogen related properties were examined (solid-gas and electrochemical reactions) in order to study their performance as negative electrode material in Ni-MH batteries
102

Metal Matrix Composites Prepared by Powder Metallurgy Route / Metal Matrix Composites Prepared by Powder Metallurgy Route

Moravčík, Igor January 2017 (has links)
Ve všeobecnosti, poznatky o design slitin, jejich výrobě a výběru legujúcich prvků sú omezené na slitiny s jedním základním prvkem. Tento fakt ale výrazně limituje možnosti a volnost výběru prvků pro dosáhnuti speciálních vlastností a mikrostruktur. V poslední dekádě se ukázalo, že materiálová věda a inženýrství nejsou ještě zdaleka prozkoumané v důsledku objevu nové třídy materiálů nazvané vysoko entropické slitiny (HEA high entropy alloys). Jejich objev upoutal pozornost vědecké komunity. Základní koncept pro jejich design je, že namísto jednoho, nebo dvou základních prvků obsahují minimálně 5 prvků v podobných atomových koncentracích. V posledních letech se objevila skupina materiálů odvozená od HEA, nazvaná slitiny so střednou entropii (MEA medium entropy alloys). Na rozdíl od HEA ale obsahují 3, nebo 4 prvky. Táto práce je věnovaná studiu přípravy a charakterizaci HEA, MEA a jejich kompozitů s pomocí metod práškové metalurgie. V této práci byli dohromady zkoumány tři kompozice: AlCoCrFeNiTi0.5, Co1.5Ni1.5CrFeTi0.5 a CoCrNi, kompozity s kovovou matricí (MMC metal matrix composites) vyztužené částicemi B4C s CoCrNi jako matricí. Hloubková mikrostrukturní a mechanická analýza těchto materiálů byla provedena pomoví metod rastrovací a transmisní elektronové mikroskopie spojené s tahovými a ohybovými zkouškami. V průběhu celé studie se objevovaly problémy s kontaminací kyslíkem, co se projevilo vznikem značného množství oxidů v připravených materiálech. U Slitiny AlCoCrFeNiTi0.5 byla naměřena tvrdost přesahující 800 HV. Její houževnatost ale byla velice omezena. V její mikrostruktuře byly identifikovány částice in-situ TiC v důsledku přítomnosti organického, anti-aglomeračního činidla (metanolu) v mlecí misce. Tato reakce může být použita v budoucnu k přípravě MMC se záměrnou disperzí TiC. Na druhé straně, slitina CoCrNi ukázala vysoké hodnoty tažnosti (26%) a meze pevnosti přes 1000 MPa. Mikrostruktura obsahovala majoritní FCC fázi s BCC precipitáty. Tahle slitina byla z důvodu vysoké tažnosti zvolena pro přípravu kompozitu s výztuží B4C. V průběhu slinování ale došlo k reakci mezi přítomným Cr a B4C, které výsledkem byl Cr5B3 borid. Tento kompozit mel pevnost v tahu 1400 MP a extrémne jemnozrnnou strukturu. Celková tažnost ale klesla na 1.9 %. Slitina AlCoCrFeNiTi0.5, která mela strukturu složenou jen z FCC tuhého roztoku dosáhla nejlepší kombinaci mechanických vlastností s pevností přesahující 1300 MPa a dostatečnou tažností 4%. Prášková metalurgie se ukázala jako vhodná metoda pro přípravu HEA a MEA slitin a jejich kompozitů, s dobrou kombinací pevnosti a tažnosti. Tato metoda dovoluje měnit mikrostrukturní parametry připravených materiálů jednoduchou úpravou parametrů procesu.
103

Pokročilé kompozitní konstrukční oceli pro použití v taveninách těžkých kovů / Advanced Composite Structural Steels for Applications in Heavy Liquid Metals

Husák, Roman January 2019 (has links)
Doctoral thesis was focused on preparing of new advanced ODS steels for use in heavy metal liquids enviroments. Possibility of new course for creating oxide dispersion in microstructure was verified by the course of internal oxidation of elements. By the internal oxidation method were prepared new ODS steels strengthened by complex oxides which were created by elements of IIIB and IVB group of elements. Based on analysis of damage ODS steels in LBE were designed surface protection of ODS steel by the oxide layer. The ODS steel protected by oxide layer was subjected to a corrosion test in LBE. For the experiments were chosen class of chromium steels: ferritic-martensitic steel 9Cr1WMnVTa and ferritic steels 14CrWTi and 17Cr1Mo. Steels without oxide dispersion and steel strenghtened by the dispersion based on Y-Ti-O oxides were prepared. On the steels were made series of mechanic tests which should reveal the effectivity of oxide dispersion on the strenght of steel prepared by the internal oxidation method and by the direct addition of oxide elements. It was found that significantly harder oxide material couldn't be fully disrupted through the mechanical alloying and fine oxide dispersion couldn't be created. There was verified fine oxide dispersion could be created by the internal oxidation method and by the direct adding of oxide elements. Same kind of steels strenghtened by new kind of complex oxides based on Y, Ce, Hf, La, Sc and Zr were prepared. The chemical analyses have proven that all added elements could created complex oxide by the reaction with yttrium. The computational analyses for observing of matrix influence and oxide phase influence on strenghtening of steels were performed. These computational analyses were based on microstructural analyses of ODS steels. There was found that the oxide particles could very effectively improve strenght of steels at room temperature and especialy at high temperature. Based on corrosion tests of 14Cr ODS steel in liquid Pb and LBE enviroment were designed surface protection of ODS steel. The effectiveness of protective layer was verified by the high temperature corrosion test of PM2000 in LBE. No damage of oxide layer was observed although Pb and Bi diffused through protective layer.
104

Příprava struktur duplexního typu cestou mechanického legování a SPS / Duplex microstructures preparation by mechanical alloying and spark plasma sintering

Neboha, Oksana January 2020 (has links)
This master´s thesis focuses on duplex microstructures preparation by powder metallurgy. A hybrid material can be created by combining two or more existing materials in different geometries, and thus the newly formed composite can provide a superposition of the properties of the starting materials (powders). This means that it will have an improved combination of the required properties. The theoretical part describes in detail the hybrid materials and the architectured materials that contain highly controlled structures. Structure control allows to change the variety of possible geometries and opens up a number of other useful properties. Therefore, this thesis also deals with the mechanical alloying and SPS. The experimental part describes procedures of preparation of four samples of composites with a duplex structure from a powder of a significantly tough alloy (austenitic steel 316L) in combination with a powder of a significantly strong alloy (titanium carbonitride). A crucial part of this thesis is characterization of these four samples by electron microscopy methods (SEM, TEM, EDS) and supported by hardness measuring.
105

ADVANCED PROCESSING OF NICKEL-TITANIUM-GRAPHITE BASED METAL MATRIX COMPOSITES

Patil, Amit k. 12 June 2019 (has links)
No description available.
106

Структура и свойства функционального интерметаллида PtAl2, полученного методом кручения под высоким давлением : магистерская диссертация / Structure and properties of functional intermetallic compound ptal2 obtained by high-pressure torsion

Кошевой, П. С., Koshevoy, P. S. January 2020 (has links)
Объект исследования – деформированные в результате интенсивной пластической деформации кручением под высоким давлением образцы на основе платины и алюминия. Цель работы – разработка технологии получения интерметаллида PtAl2 с последующим изучением микроструктуры и механических свойств полученных образцов. Методы исследования – проведение механосинтеза, изучение микроструктуры, измерение микротвердости. Результаты работы – методом кручения под высоким давлением из исходных металлических порошков получены образцы в виде пластин, содержащие интерметаллическую фазу. Образцы были исследованы в сканирующем электронном микроскопе и в рентгеновском дифрактометре. Произведены испытания микротвердости образцов. Рентгенофазовый анализ, показал наличие интерметаллида в продеформированных образцах. Новизна исследования состоит в способе получения интерметаллида PtAl2 путем механосинтеза при комнатной температуре (методом кручения под высоким давлением). Область применения – полученные результаты могут быть использованы при создании покрытий на основе интерметаллидов PtAl2 для авиастроения и машиностроения. / Subject of the research are samples based on platinum and aluminum and deformed by using high pressure torsion. The purpose of the work is to develop a technique to produce PtAl2 intermetallic compounds with subsequent study of the microstructure and mechanical properties of the obtained samples. Research methods: carrying out mechanical alloying, studying the microstructure, conducting mechanical hardness tests of samples. As a result of the research samples in the form of plates containing an intermetallic phase were obtained by high pressure torsion the starting metal powders. Samples were examined using a scanning electron microscope and an X-ray diffractometer. The microhardness of the samples was tested. X-ray phase analysis showed the presence of intermetallic in deformed samples. The novelty of the study is to obtain intermetallic using high pressure torsion. Application field: the obtained results can be used to create PtAl22 intermetallic compounds for aircraft and machine building.
107

Desarrollo de aleaciones ß Ti-Nb-Mo mediante pulvimetalurgia para aplicaciones biomédicas

Viera Sotillo, Mauricio 27 November 2020 (has links)
[ES] Dentro del sector biomédico, el titanio y sus aleaciones han desplazado a otros materiales como el acero inoxidable 316L y las aleaciones Co-Cr por ofrecer un módulo elástico más cercano al hueso cortical, lo que reduce sustancialmente el efecto de apantallamiento de tensiones. Una manera de disminuir aún más el módulo elástico es estabilizando la fase cúbica beta (bcc) del titanio a temperatura ambiente mediante la adición de elementos como el Nb y Mo, cuya biocompatibilidad ha sido comprobada en numerosos estudios. La ruta convencional para el procesado de estas aleaciones es la fundición y/o forja, pero en esta investigación se ha optado por la pulvimetalurgia ya que el desperdicio de material es mínimo y se reducen las etapas posteriores de tratamientos térmicos y mecanizado, facilitando el procesado en general y reduciendo los costos. Además, el carácter refractario de los elementos estabilizadores beta justifica aún más el empleo de un método de consolidación en estado sólido como la pulvimetalurgia donde no es necesario alcanzar temperaturas tan elevadas. Por tanto, en una primera aproximación se han procesado aleaciones de Ti-xNb-yMo (x = 13, 20, 27, 35 ; y = 12, 10, 8, 6; % en peso) mediante pulvimetalurgia convencional para estudiar el efecto del Nb y Mo en la microestructura y propiedades mecánicas de las aleaciones. A fin de atacar otros problemas inherentes del proceso como la porosidad y la falta de homogeneidad en la microestructura se ha acudido a la mezcla mecánica de polvos de la aleación Ti-35Nb-6Mo, evaluando también el efecto de diferentes agentes controladores de proceso en la molienda. Por último, se ha tratado la superficie de las aleaciones Ti-27Nb-8Mo y Ti-35Nb-6Mo mediante fusión por láser con diferentes parámetros para estudiar la capacidad del proceso de cerrar la porosidad abierta, mejorar la homogeneidad superficial, y evaluar su efecto en la microestructura y propiedades mecánicas de las aleaciones. Pese a aumentar la porosidad en función del contenido de Nb, las aleaciones Ti-27Nb-8Mo y Ti-35Nb-6Mo de las obtenidas por mezcla elemental exhibieron las mejores propiedades en general, con una microestructura casi beta en su totalidad y un módulo de elasticidad de 67 - 74 GPa, que se acerca más al presentado por el hueso cortical en comparación con la aleación comercial Ti-6Al-4V ELI. Por su parte, la mezcla mecánica mejoró considerablemente la homogeneidad química de la aleación Ti-35Nb-6Mo, pero promovió la formación de la fase alfa y deterioró la resistencia y deformación mecánica debido a la ganancia en acritud del polvo y el aumento de la porosidad. No obstante, la microdureza de las aleaciones aumentó significativamente. En cuanto al agente controlador de proceso, el cloruro de sodio (NaCl) exhibió los mejores resultados en términos de rendimiento y distribución de tamaño de partícula, mientras que el ácido esteárico indujo la contaminación del polvo mediante la formación de la fase no deseada TiC. El tratamiento de fusión superficial por láser consiguió cerrar efectivamente la porosidad abierta de las aleaciones y mejorar la homogeneidad microestructural. Adicionalmente, promovió un aumento de la resistencia y la deformación mecánica y una leve disminución del módulo elástico en ambas aleaciones. Por último, la aleación Ti-27Nb-8Mo tratada superficialmente a 1000W y 6,67 mm/s exhibió una microestructura beta casi en su totalidad y las mejores propiedades mecánicas desde un punto de vista biomédico, con una resistencia de 1467 MPa, una deformación de 7% y un módulo de elasticidad de 67 - 72 GPa. / [CA] Dins del sector biomèdic el titani i els seus aliatges han desplaçat a altres materials com l'acer inoxidable 316L i els aliatges Co-Cr per oferir un mòdul elàstic inferior i més pròxim a l'os cortical, la qual cosa redueix substancialment l'efecte d'apantallament de tensions. Una manera de disminuir encara més el mòdul elàstic és estabilitzant la fase cúbica beta; (bcc) del titani a temperatura ambient mitjançant l'addició d'elements altament biocompatibles com el Nb i Mo. La ruta convencional per al processament d'aquests aliatges és la fosa i/o forja, però en aquesta recerca s'ha optat per la pulvimetalurgia ja que el desaprofitament de material és mínim i es redueixen les etapes posteriors de tractament tèrmics i mecanitzat, facilitant el processament en general i reduint els costos. A més, el caràcter refractari dels elements estabilitzadors beta justifica encara més l'ús d'un mètode de consolidació en estat sòlid com la pulvimetalurgia on no és necessari aconseguir temperatures tan elevada. Per tant, en una primera aproximació s'han processat aliatges de Tu-xNb-yMo (x = 13, 20, 27, 35 ; i = 12, 10, 8, 6; % en pes) mitjançant pulvimetalurgia convencional per a estudiar l'efecte del Nb i Mo en la microestructura i propietats mecàniques dels aliatges. A fi d'atacar altres problemes inherents del procés com la porositat i la falta d'homogeneïtat en la microestructura s'ha acudit a la mescla mecànica de pólvores de l'aliatge Tu-35Nb-6Mo, avaluant també l'efecte de diferents agents antiadherentes en la mòltaa. Finalment, s'ha tractat la superfície dels aliatges Tu-27Nb-8Mo i Tu-35Nb-6Mo mitjançant fusió per làser amb diferents paràmetres per a estudiar la capacitat del procés per a tancar la porositat oberta, millorar l'homogeneïtat superficial, i avaluar el seu efecte en la microestructura i propietats mecàniques dels aliatges. Malgrat augmentar la porositat en funció del contingut de Nb, els aliatges Tu-27Nb-8Mo i Tu-35Nb-6Mo van exhibir les millors propietats en general. La mescla mecànica va millorar l'homogeneïtat química de l'aliatge Tu-35Nb-6Mo però va deteriorar les propietats mecàniques amb excepció de la microdureza. El tractament de fusió superficial per làser va aconseguir tancar efectivament la porositat oberta dels aliatges i va millorar l'homogeneïtat microestructural i les propietats mecàniques. Finalment, l'aliatge Tu-27Nb-8Mo tractada superficialment a 1000W i 6,67 mm/s va exhibir una microestructura beta gairebé íntegrament i les millors propietats mecàniques des d'un punt de vista biomèdic. / [EN] Within the biomedical sector, titanium and its alloys have replaced other materials such as 316L stainless steel and Co-Cr alloys due to a lower elastic modulus, closer to the cortical bone, which significantly reduces the stress shielding effect. An alternative to decrease the elastic modulus even more is to stabilize the cubic beta phase (bcc) of titanium at room temperature by adding highly biocompatible elements such as Nb and Mo. These alloys are normally processed by casting and/or forging, but in this work powder metallurgy was conducted due to lower material waste and less subsequent stages of heat treatments and machining, reducing costs significantly. Moreover, the refractory nature of beta stabilizing elements justifies even more the use of a solid-state consolidation method such as powder metallurgy where it is not necessary to reach meting point temperatures. Therefore, in a first approach, Ti-xNb-yMo alloys (x = 13, 20, 27, 35; y = 12, 10, 8, 6;% by weight) were processed by conventional powder metallurgy to study the effect of Nb and Mo in the microstructure and mechanical properties of the alloys. In order to attack other powder metallurgy inherent problems, such as porosity and inhomogeneity in the microstructure, mechanical mixing was carried out for the Ti-35Nb-6Mo powder, evaluating the effect of different non-stick agents on the milling process. Finally, the surface of Ti-27Nb-8Mo and Ti-35Nb-6Mo alloys were treated by laser surface melting under different parameters to reduce open porosity, improve surface homogeneity, and evaluate its effect. in the microstructure and mechanical properties of alloys. Despite increasing porosity with the increase of Nb content, Ti-27Nb-8Mo and Ti-35Nb-6Mo alloys exhibited the best overall properties, consisting of a beta phase microstructure. Mechanical mixing improved the chemical homogeneity of the Ti-35Nb-6Mo alloy but deteriorated the mechanical properties with the exception of microhardness. The laser surface melting treatment effectively closed the open porosity in the alloys and improved the microstructural homogeneity and mechanical properties. Lastly, the Ti-27Nb-8Mo alloy which surface was treated at 1000W and 6.67 mm/s exhibited a beta microstructure and the best mechanical properties from a biomedical point of view. Despite increasing porosity with Nb addition, Ti-27Nb-8Mo and Ti-35Nb-6Mo alloys exhibited the best overall properties, both consisting of a beta phase microstructure and an elastic modulus of 67 - 74 GPa, which is closer to the cortical bone in comparison to the commercial Ti-6Al-4V ELI alloy. On the other hand, the mechanical mixing significantly improved the chemical homogeneity of the Ti-35Nb-6Mo alloy, but induced the formation of alfa phase and deteriorated the resistance and mechanical deformation due to the increase in porosity and the hardening effect produced during the milling process. Therefore, the microhardness increased significantly. Regarding the process control agent, sodium chloride (NaCl) exhibited the best results in terms of powder yield and particle size distribution, while stearic acid induced contamination by the formation of the undesired TiC phase. The laser surface melting treatment was able to effectively close the open porosity of the alloys and improve microstructural homogeneity. Moreover, it promoted an increase in strength and mechanical deformation and a slight decrease in the elastic modulus in both alloys. Finally, the surface-treated Ti-27Nb-8Mo alloy at 1000W and 6.67 mm/s exhibited almost an entirely beta phase microstructure and the best mechanical properties from a biomedical point of view, with a resistance of 1467 MPa, a deformation of 7% and a modulus of elasticity of 67 - 72 GPa. / El trabajo se realizó en el Instituto de Tecnología de Materiales y en el Departamento de Ingeniería Mecánica y de Materiales de la Universitat Politècnica de València, bajo la ayuda del proyecto MAT2014-53764-C3-1-R del Ministerio de Economía y Competitividad de España, y la subvención 2016/020 del programa SANTIAGO GRISOLIA, enmarcada en la convocatoria del 2015 de la Conselleria de Educación, Cultura y Deporte de la Generalitat Valenciana. / Viera Sotillo, M. (2020). Desarrollo de aleaciones ß Ti-Nb-Mo mediante pulvimetalurgia para aplicaciones biomédicas [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/156194
108

Structural Characterization and Thermoelectric Performance of ZrNiSn Half-Heusler Compound Synthesized by Mechanical Alloying

Germond, Jeffrey 14 May 2010 (has links)
Thermoelectric (TE) ZrNiSn samples with a half-Heusler atomic structure were synthesized by mechanical alloying (MA) and consolidation by either Spark Plasma Sintering (SPS) or hot pressing (HP). X-Ray diffraction patterns of as milled powders and consolidated samples were compared and analyzed for phase purity. Thermal conductivity, electrical conductivity and Seebeck coefficient are measured as a function of temperature in the range 300 K to 800 K and compared with measurements reported for high temperature solid state reaction synthesis of this compound. HP samples, compared to SPS samples, demonstrate increased grain growth due to longer heating times. Reduced grain size achieved by MA and SPS causes increased phonon scattering due to the increased number of grain boundaries, which lowers the thermal conductivity without doping the base system with addition phonon scattering centers. Mechanical characterization of the samples by microindentation and depth sensing indentation for hardness and elastic modulus will be discussed.
109

Caracterização do polietileno de ultra alta massa molar processado por moagem de alta energia

Mendes, Luciana Biagini 05 August 2010 (has links)
Made available in DSpace on 2017-07-21T20:42:32Z (GMT). No. of bitstreams: 1 Luciana Biagini Mendes.pdf: 7206159 bytes, checksum: d493f2f21ec603c56bf971cd0445a8f6 (MD5) Previous issue date: 2010-08-05 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This research was an exploratory study of the changes that high energy mechanical milling can induce in ultra high molecular weight polyethylene (UHMWPE), using the mills Spex, Attritor and Planetary, and several times and reasons for grinding. The milling products were characterized using scanning electron microscopy (SEM), optical microscopy (OM), differential scanning calorimeter (DSC), x-ray diffraction (XRD), x-ray fluorescence (XRF), and intrinsic viscosity for calculate the viscosity average molecular weight. For the analysis of micrographs observed the morphological change of particles with the grinding, the particles are initially rounded and the milling time increases the aspect ratio, acquire the form of flakes. Changing the shape in Spex mill occurs in less time, because it is a mill more energetic that Attritor and Planetary. By analysis of DSC was possible to observe the influence of high energy mechanical milling on melting and crystallization temperatures, and the percentage of crystalline phase of UHMWPE. Was used deconvolution of peaks in xray diffraction patterns for better identification of the peaks of monoclinic and orthorhombic crystalline structures. Observed the formation of monoclinic phase in the UHMWPE processed in high energy mills, to a greater percentage in the mill Attritor, possibly because it has a temperature control and avoiding a reversal of the monoclinic crystalline structure in orthorhombic crystalline structure. / Este trabalho foi realizado para um estudo exploratório das modificações que a moagem de alta energia pode provocar no polietileno de ultra alta massa molar (PEUAMM), utilizando os moinhos Spex, Attritor e Planetário, e variando tempo e poder de moagem. Os produtos de moagem foram caracterizados utilizando microscopia eletrônica de varredura (MEV), microscopia ótica (MO), calorimetria exploratória diferencial (DSC), difração de raios x (DRX), fluorescência de raios x (FRX), e medidas de viscosidade intrínseca para o cálculo da massa molar viscosimétrica média. Pelas análises das micrografias observou-se a mudança morfológica das partículas com a moagem, inicialmente as partículas são arredondadas e com o tempo de moagem aumentam a razão de aspecto, adquirem a forma de flakes. Para o moinho Spex a mudança da forma das partículas ocorre em menor tempo, por este ser um moinho mais energético que o Attritor e Planetário. Pela análise do DSC foi possível observar a influência da moagem de alta energia nas temperaturas de fusão e cristalização, e na porcentagem de fase cristalina do PEUAMM. Foi utilizada a deconvolução de picos nos difratogramas de raios x para melhor identificação dos picos das estruturas cristalinas ortorrômbica e monoclínica. Com a moagem de alta energia ocorreu a formação da estrutura cristalina metaestável monoclínica, em maior porcentagem no moinho Attritor, possivelmente por este possuir um controle de temperatura e evitando uma reversão da estrutura cristalina monoclínica em ortorrômbica.
110

Mecano-síntese e caracterização de ligas de Ti-Nb-Sn

Muradás, Rodrigo Ricabone 31 October 2006 (has links)
Made available in DSpace on 2017-07-21T20:42:35Z (GMT). No. of bitstreams: 1 rodrigoric.pdf: 9183178 bytes, checksum: 1d5fba078a589cbc1810eea245d1e019 (MD5) Previous issue date: 2006-10-31 / Mechanical alloying is a powder processing technique involving cold welding, fracturing mechanisms and rewelding of powder particles in a ball mill. The present work applied this technique with the purpose of processing titanium, niobium and tin alloys, through planetary ball mill and attritor mill. The atomic percentages of these elements were varied in six differents ways. The niobium hydrate was used on production of some alloys in study, with the purpose to observe the effects during the milling and on the alloys obtained after sintering. Differences between processing in planetary ball mill and attritor mill, as well the cold welding influences on the kinetic parameters of milling process were approached. The use of niobium hydrate result in a decrease of powders average crystallite size, and an increase of micro hardness of sintered alloys. This work obtained beta titanium alloys and alpha-beta titanium alloys in namometric sizes. The average crystallite size, for milled powders, was 7,6 nm. / Mecano-síntese é uma técnica de processamento em pó que envolve a soldagem a frio, mecanismos de fratura e a resoldagem das partículas de pós, em moinhos de bolas. O presente trabalho utilizou esta técnica com o propósito de processar ligas de titânio, nióbio e estanho, através de moinhos de bolas planetário e de atrito. As porcentagens atômicas destes elementos foram variadas de seis maneiras diferentes. O hidreto de nióbio foi utilizado na produção de algumas ligas em estudo, com o propósito de se observar os efeitos durante a moagem e na liga obtida após a sinterização. Diferenças entre o processamento em moinho de bolas planetário e o moinho de atrito, assim como as influências da soldagem a frio nos parâmetros cinéticos do processo de moagem, foram abordadas. O uso do hidreto de nióbio resultou na diminuição do tamanho médio de cristalito dos pós, e em um acréscimo na microdureza das ligas sinterizadas. Neste trabalho foram obtidas ligas de titânio beta e de titânio alfa-beta, em tamanhos nanométricos. O tamanho médio do cristalito, para os pós moídos, foi de 7,6 nm.

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