Biomateriais para uso em implantes devem exibir propriedades como biocompatibilidade, biofuncionalidade e resistência à corrosão. O uso do titânio e suas ligas em aplicações biomédicas vem continuamente aumentando devido à sua maior taxa resistência-peso, superior biocompatibilidade e resistência à corrosão, boas propriedades mecânicas e baixo módulo de elasticidade quando comparado a outros materiais biomateriais metálicos como aço inox e ligas Co-Cr. Um importante aspecto para o sucesso de um implante é a utilização de materiais com módulo de elasticidade baixo, próximo ao do osso, pois estudos indicam que a transferência insuficiente de carga entre implante e osso pode resultar em reabsorção óssea e afrouxamento do implante, que é chamado efeito de blindagem de tensão (stress shielding effect). A liga ternária Ti13Nb13Zr apresenta em sua composição somente elementos considerados biocompatíveis, possui menor módulo de elasticidade que ligas Co-Cr, aço inox e Ti6Al4V, e superior resistência à corrosão. Neste trabalho foi estudado o efeito do teor de nióbio e zircônio nas propriedades mecânicas da liga ternária TiNbZr numa faixa de composições com quantidade de titânio constante em 74 %peso e teor de Nb e Zr variando entre 6 e 20 %peso, produzida por metalurgia do pó a partir de pós hidrogenados e método de mistura elementar, após diferentes condições de processamento e tratamentos térmicos. Os resultados de caracterização microestrutural obtidos por MEV e difração de raios X mostraram que o aumento do teor de Nb não produziu alterações significativas na fração volumétrica das fases e e, o aumento do teor de Zr proporcionou o aumento da fração de fase , favorecendo a formação da estrutura de Widmanstätten. O aumento dos teores de Nb e Zr produziram alterações nas microestruturas dos materiais que levaram ao aumento dos valores de módulo de elasticidade e dureza, e com aumento do teor de Zr houve aumento da susceptibilidade à corrosão. Nas condições de processamento utilizadas, a liga Ti13Nb13Zr apresentou as propriedades mecânicas e microestruturais mais indicadas para utilização como biomateriais. / Biomaterials for use in implants must be biocompatible, biofunctional and resistant to corrosion. Utilization of titanium and its alloys is continuously increasing due to their larger strength-weight ratio, superior biocompatibility e corrosion resistance, good mechanical properties and low elastic modulus when compared to other metallic biomaterials such as stainless steel and Co-Cr alloys. Using materials with low elastic modulus, close to bone values, is important to reduce stress shielding effect, which can cause implant loosening. Ti13Nb13Zr ternary alloy shows only elements considered biocompatible and has a lower elastic modulus than Co-Cr alloy, stainless steel and Ti6Al4V, and superior corrosion resistance. In this work TiNbZr alloy was prepared in different compositions, maintaining Ti content at 74%wt with Nb and Zr contents ranging amongst 6 and 20%wt, produced by powder metallurgy using different processing conditions and heat treatments. Characterization via SEM and X-Ray diffraction showed that the Nb increase didnt produce significant alterations on volume fraction of and phases in the material, and the increase in Zr content led to an increase in phase amounts and formation of Widmanstätten patterns. Nb and Zr content increasing produced microstructural modifications, leading to an increase in elastic modulus and hardness values, as well as corrosion susceptibility variations, where higher Zr contents leaded to a surface with less corrosion resistance. Amongst compositions and for the designed processing method, Ti13Nb13Zr presented the most indicated mechanical and microstructural properties for utilization as biomaterials.

Orientador: Rubens Caram Junior / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-12T05:26:08Z (GMT). No. of bitstreams: 1 Souza_SandraAndreiaStwartdeAraujo_D.pdf: 29406912 bytes, checksum: 599ca950936f4d1a34c07ae03af24fb6 (MD5) Previous issue date: 2008 / Resumo: Freqüentemente, os implantes femorais falham devido à transferência insuficiente de carregamento a partir da haste metálica para o osso adjacente. Este problema está relacionado à diferença de rigidez entre osso e prótese, que depende em parte de seus módulos de elasticidade. Dessa forma, ligas com módulos de elasticidade menores são desejáveis, a fim de melhorar a distribuição de tensões nos tecidos ósseos adjacentes. Adições de Nb e Ta ao titânio propiciam a redução do módulo de elasticidade, além de não provocarem reação alérgica nos tecidos ao redor do implante. Como as propriedades das ligas de titânio são fortemente dependentes de suas fases constituintes, este estudo teve como objetivo avaliar o efeito da taxa de resfriamento sobre as transformações de fases das ligas Ti-(25; 30; 35)%Nb-(0; 2,5; 5; 7,5)%Ta (% em peso), com ênfase na identificação das relações entre propriedades e microestrutura. Assim, foi verificado que as adições desses elementos promoveram a formação das fases a", ß-metaestável e ? em uma ampla faixa de taxas de resfriamento e que a dureza e o módulo de elasticidade das ligas foram fortemente influenciados pela precipitação da fase ?. Em geral, as ligas submetidas a altas taxas de resfriamento apresentaram limite de escoamento variando de 303 a 457 MPa e alongamento variando de 6 a 38%. As ligas Ti-35Nb e Ti-35Nb-7,5Ta foram também envelhecidas e os resultados obtidos mostraram que a liga Ti-35Nb-7,5Ta apresenta a melhor combinação entre alta resistência mecânica e baixo módulo de elasticidade. / Abstract: Life time of femoral implants is usually shortened by insufficient transfer of load from implant to adjacent bone; this problem is attributed to the different stiffness of bone and implant that partially depends on their elastic moduli. Therefore, alloys exhibiting lower values of elastic modulus are desirable in order to improve the distribution of stress in the adjacent bone tissue. On this purpose, additions of Nb and Ta to titanium permit to reduce the elastic modulus, not provoking allergic reactions. Since properties of titanium alloys are strongly dependent on their constituent phases, this study aims to evaluate the effect of cooling rates on the phase transformations of the Ti-(25; 30; 35)%Nb-(0; 2.5; 5; 7.5)%Ta (wt. %) alloys; the work is focused on identifying the microstructure-property relationship. Thus, it was observed that additions of the alloying elements led to the formation of a", ß-metastable and ? phases in a wide range of cooling rates. Moreover, ? phase precipitation strongly influences hardness and elastic modulus. When cooled at high cooling rates the alloys presented yield strength ranging from 303 to 457 MPa and elongation ranging from 6 to 38%. Aging treatments were also applied to the Ti- 35Nb and Ti-35Nb-7.5Ta alloys and the results show that the Ti-35Nb-7.5Ta alloy presents the best combination between high strength and low modulus. / Doutorado / Materiais e Processos de Fabricação / Doutor em Engenharia Mecânica

Orientador: João Batista Fogagnolo / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-24T20:13:02Z (GMT). No. of bitstreams: 1 Carvalho_LisianeRochaAzevedode_M.pdf: 2047962 bytes, checksum: 5f5e3ae6c55b6c8a79673f40d2fc559a (MD5) Previous issue date: 2014 / Resumo: Titânio e suas ligas são amplamente utilizados como biomateriais devido a propriedades como alta resistência específica, alta resistência à corrosão e baixo módulo de elasticidade. As ligas de titânio apresentam diferentes estruturas cristalinas, as quais possuem diferentes módulos de elasticidade. Esta característica permite que o módulo de elasticidade seja manipulado através do controle da composição química da peça, o que por sua vez possibilita a fabricação de peças com gradientes de rigidez, abrindo-se um amplo campo de pesquisa e novas aplicações. Este trabalho utiliza a técnica de modificação superficial por laser e adição de nióbio com o objetivo de obter peças de titânio com revestimentos constituídos por fases com menores módulos de elasticidade, ou seja, peças com revestimentos menos rígidos que o substrato. Inicialmente foram caracterizados cordões isolados obtidos com diferentes densidades de energia do feixe de laser, através da variação da potência, do diâmetro e da velocidade de varredura do feixe de laser. Nos cordões isolados, observou-se que a potência do feixe de laser é o parâmetro de maior influência e que densidades de energia intermediárias possibilitaram obter cordões com zonas fundidas com dimensões e formato adequados para a posterior etapa de obtenção de recobrimento contínuo por sobreposição de cordões. As composições dos cordões isolados, apesar de apresentar heterogeneidade, permitiram a estabilização da fase ?. No entanto, uma fração significativa dos cordões apresentou também a fase ? com microestrutura dendrítica, indicando que essa fase foi resultado da solidificação, o que pode ter ocorrido pela contaminação por oxigênio, que é um forte estabilizador dessa fase. Dessa forma, mesmo com a formação da fase ?, não se observou uma redução do módulo de elasticidade. Em todos os casos, a dureza apresentou um significativo aumento, também devido a forte contaminação por oxigênio. A formação de revestimentos contínuos foi obtida através da sobreposição de 50% da largura dos cordões. Os revestimentos contínuos assim obtidos apresentaram segregação de soluto, com fase ? estabilizada nas regiões com maiores teores de nióbio e agulhas de martensita nas regiões com menores teores de nióbio. A contaminação por oxigênio foi reduzida em comparação com os cordões isolados. Os revestimentos contínuos apresentaram aumento de dureza e diminuição do módulo de elasticidade, conforme o objetivo proposto / Abstract: Titanium and its alloys are commonly used as biomaterials due to their properties as high specific strength, high corrosion resistance and low elastic modulus. Titanium alloys show differents crystalline structures, which have different elastic modulus. This characteristic allows the manipulation of the elastic modulus through chemical composition control, which allows the manufacture of pieces with stiffness gradients, spreading a large research field and new applications. This work use the laser surface alloying technique with addition of niobium powder to obtain titanium pieces with coatings composed by phases with lower elastic modulus, in other words, pieces with coatings less stiff than the substrate. Firstly, isolated tracks obtained by different beam laser energy densities, by varying laser beam power, diameter and scan speed were characterized. In this case, the laser beam power was the most important parameter and the intermediaries energy densities allowed to obtain tracks with melted zones with dimensions and shape suitable to obtain a continuous coating by overlapping tracks. The isolated tracks compositions, despite their chemical heterogeneities, showed the stabilization of the ? phase. However, a significant fraction of tracks showed also ? phase with dendritic microstructure, indicating that this phase was the result of solidification, which may have occurred due oxygen contamination, which is a strong ? stabilizer element. Thus, despite the stabilization of the ? phase, a reduction in elastic modulus was not observed. In all the cases the hardness showed a significant increase, also because of the high contamination by oxygen. The continuous coating formation was obtained by overlapping 50% of the tracks width. The continuous coatings obtained showed solution segregation, with ? phase stabilized in the regions with higher niobium content and needle like traces of martensite in the regions with less niobium content. The oxygen contamination was reduced in comparison with isolated tracks. The continuous coatings showed high hardness with a decrease of the elastic modulus, in accordance with the proposed objective / Mestrado / Materiais e Processos de Fabricação / Mestra em Engenharia Mecânica

Orientador: Rubens Caram Júnior / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-23T11:47:28Z (GMT). No. of bitstreams: 1 Opini_VictorCarvalho_M.pdf: 4901209 bytes, checksum: 0a9d16713cdd0fd8ab69b7f9768812bc (MD5) Previous issue date: 2012 / Resumo: Em segmentos industriais bastante distintos como o aeroespacial e o médico, o uso de titânio e suas ligas na fabricação de dispositivos tem aumentado de forma consistente nos últimos anos. O emprego desse metal de forma tão diversificada, seja em motores a jatos ou em implantes ortopédicos, se deve a suas características únicas, ou seja, elevada resistência mecânica, baixa densidade, alta resistência à corrosão e ótima biocompatibilidade. Estudos realizados nos últimos anos e associados ao uso estrutural do titânio nos setores aeroespacial e médico/odontológico têm focado o desenvolvimento de ligas de titânio tipo ? metaestáveis. O presente estudo tem como objetivo discutir a preparação, processamento e caracterização da liga metaestável Ti-5553 (Ti-5Al-5V-5Mo-3Cr-0,5Fe) e de outras duas ligas com composições modificadas pela adição de nióbio em substituição ao vanádio. Tais ligas foram preparadas por meio de fusão em forno a arco, deformadas plasticamente a quente por forjamento a quente e submetidas a dois diferentes tratamentos térmicos de envelhecimento: BASCA (Beta-annealed Slow Cooled and Age) e STA (Solution Treatment and Age). Na etapa de caracterização foram utilizadas as técnicas de microscopia óptica e eletrônica de varredura, medidas de módulo de elasticidade, medidas de dureza Vickers e ensaios de tração. Os resultados indicam que a substituição do vanádio pelo nióbio não modificou as principais características da liga Ti-5553, particularmente, sua elevada resistência mecânica e baixa cinética de transformações de fases. O tratamento térmico BASCA resultou em maior ductilidade, enquanto que o tratamento STA resultou em maior limite de resistência. À medida que o V foi substituído pelo Nb, amostras submetidas ao tratamento térmico BASCA tiveram suas respectivas resistências mecânicas aumentadas, passando de 1.147 MPa para 1.227 MPa. À medida que o teor de Nb aumentou, a ductilidade reduziu-se de 10,3 % para 6,8 %. Por outro lado, amostras submetidas ao tratamento STA apresentaram redução de resistência mecânica com o aumento do teor de Nb, enquanto que a ductilidade foi levemente reduzida. Em geral, a substituição do V pelo Nb não resultou em alterações significativas no comportamento mecânico da liga Ti-5553 / Abstract: In well different industrial segments such as aerospace and medical, the use of titanium and its alloys in the manufacturing of devices has increased consistently in recent years. The use of such metal in so diverse manner, either in jet engines or orthopedic implants, is due to its unique characteristics, specifically high mechanical strength, low density, high corrosion resistance and good biocompatibility. Recent studies associated with the structural use of titanium in the aerospace and medical/dental sectors have focused on the development of ? metastable titanium alloys. This study aims to discuss the preparation, processing and characterization of the ? metastable Ti-5553 alloy (Ti-5Al-5V-5Mo-3Cr-0.5Fe) and two alloys with compositions modified by the addition of niobium to replace vanadium. Such alloys were prepared by arc melting, deformed plastically by hot forging and submitted to two different aging heat treatments: BASCA (Beta-annealed Slow Cooled and Age) and STA (Solution Treatment and Age). Characterization was carried out by applying optical microscopy and scanning electron microscopy, measurements of elastic modulus, Vickers hardness and tensile tests. The results suggest that the replacement of vanadium by niobium does not modify the main characteristics of the Ti-5553, particularly, its high mechanical strength and the low kinetic of phase transformations. Application of the BASCA heat treatment resulted in higher ductility, while the STA treatment resulted in higher tensile strength. As V was replaced by Nb, samples subjected to BASCA heat treatment had their mechanical strengths increased, from 1147 MPa to 1227 MPa. As the Nb content increased, ductility dropped from 10.3% to 6.8%. On the other hand, samples subjected to STA presented a decrease in mechanical strength with increasing Nb content, while ductility was slightly reduced. In general, the replacement of V by Nb has not resulted in significant changes in the Ti-5553 alloy mechanical behavior / Mestrado / Materiais e Processos de Fabricação / Mestre em Engenharia Mecânica

Orientador: Cecília Amélia de Carvalho Zavaglia, Maria Aparecida Larosa / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-23T16:17:14Z (GMT). No. of bitstreams: 1 Su_WiliamTean_M.pdf: 6069585 bytes, checksum: 37502918a2190ac353153a8e20d78e0c (MD5) Previous issue date: 2013 / Resumo: Atualmente, o mercado automotivo tem buscado cada vez mais a redução de peso e aumento de resistência mecânica de seus componentes. Dentro deste contexto, este trabalho tem como objetivo verificar se uma biela automotiva feita da liga de titânio Ti-6Al-4V obtida pelo processo de manufatura aditiva chamado Sinterização Direta de Metais por Laser (DMLS) apresenta os mesmos resultados estruturais que uma biela de Ti-6Al-4V laminada e recozida (comercial) ou que uma biela feita de aço C70, bastante utilizada no mercado. A liga Ti-6Al-4V é utilizada principalmente nas áreas aeronáutica e biomédica, mas também possui aplicações na indústria automotiva, principalmente no segmento de alta performance, graças a fatores como boa resistência mecânica, excelente resistência à corrosão e baixa densidade. As características mecânicas e microestruturais de amostras da liga Ti-6Al-4V prototipada por DMLS e de amostras da liga Ti-6Al-4V laminada e recozida foram avaliadas e comparadas através de ensaios de tração e microdureza, de análises em microscópio óptico e eletrônico de varredura (para a verificação da microestrutura e da porosidade), de ensaios de difração de raios-X (DRX) (para a análise das fases presentes no material), da análise da composição química por espectroscopia de energia dispersiva (EDS) e da análise de densidade pelo princípio de Arquimedes. Bielas de Ti-6Al-4V também foram produzidas por DMLS e ensaios de tração experimentais foram realizados, simulando uma condição de contorno típica utilizada em desenvolvimentos de bielas pela indústria automotiva. Com base nos resultados experimentais, foram realizadas análises de elementos finitos utilizando a mesma condição de contorno dos ensaios, com o intuito de se obter uma correlação entre os resultados experimentais e os virtuais. De uma maneira geral, todos os resultados indicam que a biela de Ti-6Al-4V produzida pelo processo DMLS possui um comportamento estrutural similar à biela de Ti-6Al-4V laminada e recozida / Abstract: Nowadays, the automotive market has been looking for more and more lightweight and better strength components. In this context, the objective of this work is to verify if a connecting rod made of the titanium alloy Ti-6Al-4V produced by an additive manufacturing process named Direct Metal Laser Sintering (DMLS) would have equivalent structural results of a connecting rod made of rolled annealed Ti-6AL-4V or even the C70 steel (widely used on the market for this application). This Titanium alloy is primary used in aerospace and biomedical areas, but is also used in the automotive industry, especially on the high performance segment, due to factors like good mechanical strength, excellent corrosion resistance and low density. The mechanical and microstrutural properties of Ti-6Al-4V samples obtained by DMLS and rolling and annealing processes were compared through the realization of tensile and micro hardness tests and through the microstructural characterization, composed of scanning electron microscopy (microstructure verification), optical microscopy (porosity verification), X-ray diffraction analysis for phases quantification, energy dispersive spectroscopy (chemical composition verification) and density analysis using the Arquimedes principle. Ti-6Al-4V connecting rods were also produced by the DMLS process and tensile experimental tests were performed using the same boundary condition as commonly seen on connecting rod development at automotive industry. Based on the experimental results, finite element analyses were performed in order to correlate the experimental and the virtual results. Generally, all the results indicate that the Ti-6Al-4V connecting rod produced by DMLS process has a structural behavior similar to the Ti-6Al-4V connecting rod produced by rolling and annealing process / Mestrado / Materiais e Processos de Fabricação / Mestre em Engenharia Mecânica

Les travaux effectués concernent le développement et la caractérisation de nouveaux alliages de titane à grande déformation, combinant des effets TRIP (« Transformation Induced Plasticity ») et TWIP (Twinning Induced Plasticity »). Ils s’inscrivent dans le cadre de la recherche de technologies plus économiques en termes de coûts énergétiques, nécessitant en particulier le développement de matériaux structuraux légers et performants avec une résistance, une ténacité et une ductilité exceptionnelles. Nous avons d’abord utilisé une approche semi-empirique, combinant calculs théoriques et données expérimentales, comme méthode de conception de ces nouveaux alliages. Basée sur des paramètres électroniques, cette approche permet de contrôler le degré de stabilité de la phase β du titane. Cette métallurgie, appelée métallurgie combinatoire, nous a permis de développer rapidement 3 nouvelles nuances d’alliages, qui sont : le Ti-8.5Cr-1.5Sn, Ti-8.5Cr-1.5Al, et le Ti-10V-4Cr-1Al. Il s’avère que plusieurs mécanismes de déformation sont déclenchés pour accommoder plastiquement le matériau, lors d’une sollicitation mécanique externe. Parmi ces mécanismes, sont présents le maclage {332}⟨113⟩, la martensite sous contrainte, et le glissement des dislocations. Nous avons montré que leur synergie donnée naissance à deux effets, un effet de raffinement microstructural dit « effet Hall & Petch dynamique », et un effet assimilable aux interactions matrice-renforts, appelé « effet Composite ». Nous avons mené ensuite une campagne d’essais balistiques comparative avec d’autres alliages de titane, pour analyser le comportement à l’endommagement, au plus proche d’une potentielle application industrielle. Nous avons montré que les alliages ayant la capacité d’être transformable par déformation sont ceux qui possèdent la ténacité (KIC) et la résilience (KCV) la plus élevée. Enfin, dans une dernière partie, axée sur l’ouverture de cette thématique, nous avons étudié dans un premier temps la transposition de la méthode de conception à un alliage industriel. Puis, dans un deuxième temps, une transposition des effets TRIP/TWIP à des matrices α+β, dont les résultats prometteurs des propriétés mécaniques offrent de nouvelles perspectives. / The work carried out concerns the development and characterization of new high deformation titanium alloys, combining TRIP (Transformation Induced Plasticity) and TWIP (Twinning Induced Plasticity) effects. They are part of the search for more economical technologies in terms of energy costs, requiring in particular the development of lightweight and efficient structural materials with exceptional strength, toughness and ductility. We first used a semi-empirical approach, combining theoretical calculations and experimental data, as a method for designing these new alloys. Based on electronic parameters, this approach makes it possible to control the degree of stability of the β phase of titanium. This metallurgy, called combinatorial metallurgy, allowed us to quickly develop 3 new grades of alloys, which are : Ti-8.5Cr-1.5Sn, Ti-8.5Cr-1.5Al, and Ti-10V-4Cr-1Al. It turns out that several deformation mechanisms are triggered to plastically accommodate the material during an external mechanical stress. Among these mechanisms are the {332}⟨113⟩ twinning, the stress martensite, and the dislocation slip. We have shown that their synergy gives rise to two effects, a microstructural refinement effect called "dynamic Hall & Petch effect", and an effect comparable to the matrix-reinforcement interactions, called the "Composite effect". We then carried out a comparative ballistic test campaign with other titanium alloys, to analyze the behavior to damage, closest to a potential industrial application. We have shown that alloys with the ability to be transformable by deformation are those with the highest toughness (KIC) and resilience (KCV). Finally, in a final part, focusing on the opening of this thematic, we first studied the transposition of the design method to an industrial alloy. Then, a transposition of the TRIP / TWIP effects to α+β matrices, whose promising results of mechanical properties offer new perspectives.Keywords : Titanium alloys, Twinning, Strain-hardening, Deformation microstructure, Martensitic phase transformation.

Dans le domaine des biomatériaux, les alliages de titane sont parmi les matériaux les plus attractifs pour les implants ostéointégrés grâce à leur forte résistance à la biocorrosion, une meilleure biocompatibilité et de bonnes propriétés mécaniques spécifiques. Parmi ces propriétés, le faible module élastique des alliages de titane a fortement attiré l'attention par rapport à la transmission des contraintes fonctionnelles de l'implant à l'os environnant. L'objectif de ce travail de thèse consiste à obtenir des alliages de titane aux propriétés mécaniques modulables, possibles grâce au contrôle des traitements thermomécaniques. Ceci permet d'obtenir dans un premier temps un gradient d'élasticité au sein des alliages, ainsi qu'un gradient de tailles de grains dans un second temps. L'obtention de ces gradients est rendue possible grâce à la transformation martensitique réversible β ↔ α’’ ainsi qu'à la dissolution de phase ? par traitements thermiques flash. Il est également possible de contrôler les échelles microstructurales pour obtenir des matériaux nanostructurés, homogènes et stables thermiquement, permettant de mettre en évidence un comportement superplastique à basse température. Ces derniers résultats sont susceptibles de présenter une très bonne alternative aux procédés de SPD utilisés couramment. Une caractérisation complète de ces nouveaux matériaux est réalisée en combinant analyses MEB, MET et DRX. Les valeurs de modules élastiques sont obtenues par essais de traction et localement, par mesures de microindentation instrumentée. / In the field of biomaterials, titanium alloys are among the most attractive materials for osseointegrated implants due to their high biocorrosion resistance, increased general biocompatibility and specific mechanical properties. Among these properties, low elastic modulus of titanium alloys has attracted much attention regarding the transmission of functional loads from the implant to the surrounding bone. The aim of this work consists in developing functionally graded materials, with careful attention to the thermomechanical treatments. In one hand, this allows us to obtain a gradient of elasticity in bulk materials and in the other hand, a gradient of grain sizes. This is possible thanks to the reversible martensitic transformation β ↔ α’’ and also to the α phase dissolution during flash treatments. The microstructural scale is also controlled in order to develop homogeneous materials at the nanoscale, thermally stables, and exhibiting superplasticity at low temperatures. These results are thought to be good strategy to avoid the use of SPD processes. A complete characterization of these new materials is performed with the combination of SEM, TEM and XRD analyses to appreciate the modifications of the microstructures and grain sizes. Values of elastic modulus are obtained by tensile tests, and locally determined with the use of instrumented microindentation measurements.

Le présent travail de thèse a pour but le développement du procédé de traitement de surface d’anodisation micro-arc (MAO), appliqué au titane et alliage de titane. L’objectif est de déterminer l’influence des paramètres tels que la nature du substrat (éléments d’alliage), la chimie de la solution électrolytique et les paramètres électriques, sur le comportement électrochimique in-situ des couches en formation, ainsi que sur les caractéristiques microstructurales et chimiques des revêtements. Des méthodes de caractérisations notamment morphologiques (imagerie MEB et MET), chimiques (EDS, DRX, diffraction des électrons, EELS) et électrochimiques ex-situ (potentiel libre, courbes de polarisation, SIE) sont utilisées afin d’étudier les revêtements formés. L’étude systématique réalisée par voltampérométrie et chronopotentiométrie a permis de différencier trois stades ou régimes d’anodisation (I/ classique, II/ micro-arc, et III/ d’arcs), caractérisés par une réponse électrochimique particulière de l’interface métal/électrolyte, et qui impacte les propriétés de revêtement finalement obtenues. Des modèles phénoménologiques sont proposés aux différents stades d’anodisation et en lien avec les paramètres du traitement MAO. Le titane commercialement pur de Grade 2 et l’alliage de titane Ti-6Al-4V (ou TA6V) ont été étudiés comparativement ; l’influence des éléments d’alliage (aluminium et vanadium) a été discutée sur la conduite du procédé. L’élaboration d’une solution électrolytique a été étudiée dans le but d’obtenir un revêtement épais, compact et composé majoritairement de titanate d’aluminium. L’incorporation dans les revêtements des éléments provenant de l’électrolyte a été discutée en lien avec la réponse électrochimique ; cette étude conduit à une proposition de mécanisme de croissance de couche où interviennent les éléments du substrat et les éléments d’alliage aux différents stades d’anodisation. L’étude des régimes pulsés unipolaires et bipolaires a permis de discuter l’effet des temps de pause et des pulsations cathodiques sur la réponse électrochimique du matériau et sur les propriétés des revêtements. L’étude du ratio des charges anodiques / cathodiques a montré qu’il s’agissait d’un paramètre essentiel pour garantir la croissance d’un revêtement à la fois épais, homogène et compact / This thesis manuscript relates to the study of process set up of an electrochemical surface treatment, called micro-arc oxidation (MAO), and applied to titanium and its alloys. The aim is to determine the influence of parameters such as nature of the substrate (alloying elements), chemistry of the electrolytic solution and electrical parameters, on the process. In-situ electrochemical behaviour of forming oxide layers is studied, as well as microstructural and chemical characteristics of formed coatings. Many methods mostly to characterize morphology (SEM, TEM imagery), chemistry (EDS, XRD, electron diffraction, EELS) and ex- situ electrochemical behaviour (OCP, polarizing, EIS) are used. Systematic study realised by voltamperometry and chronopotentiometry allowed to differentiate three anodizing stages (I/ conventional, II/ micro-arc, III/ of arcs), characterized by a particular electrochemical response of the metal/electrolyte interface, and which impacts obtained coating properties. Phenomenological models are proposed for each stage of anodizing and linked to MAO process parameters. Grade 2 commercially pure titanium and alloy Ti-6Al-4V (or TA6V) are comparatively studied; the influence of alloying elements (aluminium and vanadium) was discussed in relation with running of the process. Development of an electrolytic solution was carried out to obtain a thick and compact coating, mostly composed of aluminium titanate. Incorporation into the coating of elements from the electrolyte was discussed, and linked to in-situ electrochemical response; this study leaded to a proposed coating growth mechanism which involves elements from the substrate and from the electrolyte. Study of unipolar and bipolar pulsed regimes allowed discussing the effect of pause time and cathodic pulses on electrochemical response of the material and on coating properties. Study of the anodic / cathodic charge ratio showed it was an essential parameter to ensure growth of a thick, homogeneous and compact coating

Titanium dioxide nanoparticles were prepared using the sol-gel process. The effect of temperature and precursor concentration on particle size was investigated. The optimum conditions were then used to prepare carbon and nitrogen doped titanium dioxide (TiO2) nanoparticles. Doping was done to reduce band gap of the nanoparticles in order to utilize visible light in the photocatalytic degradation of organic compounds. A significant shift of the absorption edge to a longer wavelength (lower energy) from 420 nm to 456 nm and 420 nm to 428 nm was observed for the carbon doped and nitrogen doped TiO2 respectively. In this study, the prepared TiO2 photocatalyst was immobilized on carbon nanofibres to allow isolation and reuse of catalyst. The photocatalytic activity of the catalyst was tested using methyl orange as a model pollutant and was based on the decolourization of the dye as it was degraded. The doped TiO2 exhibited higher photocatalytic activity than the undoped TiO2. The materials prepared were characterized by XRD, TEM, SEM, FT-IR, DSC and TGA while the doped TiO2 was characterized by XPS, ESR and Raman Spectroscopy.

Un modèle a été développé pour prédire les cinétiques de transformation de phase beta → alpha dans les alliages de titane multi constitués au cours de chemins thermiques complexes. Il repose sur : (i) une simplification de la représentation géométrique des différentes morphologies communément observées dans ces alliages (grains parents bêta, phase α(allotriomorphe) aux joints des grains parents, colonies de phase α, précipités α intragranulaires) ; (ii) des lois analytiques de germination et de croissance pour les diverses morphologies de phase α; (iii) l’hypothèse d'équilibre local aux interfaces β/α, décrite par un approche de type CalPhad ; (vi) des bilans moyens de soluté dans chaque morphologie. Nous obtenons ainsi pour chaque morphologie, les cinétiques de transformation, les évolutions de leurs tailles moyennes, et enfin les évolutions de leur composition moyenne. Nous présentons tout d’abord les calculs réalisés pour un alliage ternaire TiVO, afin de montrer les potentialités du modèle. L’analyse des résultats met en avant l’influence respective de la diffusion des solutés dans les deux phases, de la morphologie des précipités formés sur la cinétique de croissance comme sur la composition moyenne des grains formés tant pour une transformation en condition isotherme qu’au cours d’un refroidissement continu ou encore d’une séquence complexe de traitement thermique (refroidissement, chauffage, refroidissement). Le modèle a également été utilisé pour calculer les cinétiques de transformation pour l’alliage industriel Ti17 et ainsi comparer les résultats calculés aux résultats expérimentaux (cinétique et microstructures) / A model has been developed which is able to predict the kinetics of beta → alpha transformation in industrial multi component titanium alloys during complex heat treatments. The model is based on: (i) a simple geometric representations of the different morphologies commonly observed in these alloys (parent α grains, α allotriomorphs (at grain boundaries), αcolonies and intragranular α precipitates); (ii) analytical nucleation and growth laws for each morphology of α phase; (iii) the assumption of local equilibrium at interfaces, handled within the CalPhaD framework; (iv) averaged solute balances in each morphology. Diffusion of solutes in both phases is considered. We thus obtain the transformation kinetics as well as mean size parameters and mean chemical composition for each morphology of the product α phase (at grain boundaries, colonies and intragranular precipitates. Calculations performed are at first presented for a ternary TiVO alloy emphasizing the potentialities of the model. The relationships between growth conditions, role of diffusion in each phase, and chemical composition for each morphology are analyzed upon isothermal holdings, cooling from the beta phase field and more complex cooling-heating sequence. The model is further used on the Ti17 industrial and results are compared to experimental transformation kinetics and microstructures