Made available in DSpace on 2014-06-11T19:27:11Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-06-22Bitstream added on 2014-06-13T20:55:49Z : No. of bitstreams: 1 nogueira_rc_me_guara.pdf: 1525094 bytes, checksum: b0dcb8b9e8f6ae12a8d680a1344a5b04 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / As ligas Ti-Nb são apropriadas para uso em implantes devido a sua alta resistência e biocompatibilidade. Um dos métodos de obter estas ligas é a metalurgia do pó, pois ele permite obter peças próximas ao seu formato final. Teorias indicam que a razão de densificação varia inversamente como uma função do tamanho da partícula. O aumento de interesse na fabricação de materiais nanoestruturados (partículas menores que 100 nm) é devido à possibilidade de obter um material sinterizado em um tempo menor e em temperaturas mais baixas, com uma melhor densificação do que pós convencionais, pois é mais reativo. Neste trabalho, após hidrogenação e moagem de alta energia por até 60 min, obteve-se pós de hidreto de titânio e hidreto de nióbio, com estrutura ultrafina/nanométrica, que auxilia o processo de difusão numa posterior etapa de sinterização. Meios de moagem de diferentes materiais (aço inoxidável e nitreto de silício - Si3N4) foram usados. Independentemente dos meios de moagem usados, o material obtido apresentou aproximadamente 5% das partículas com valores cumulativos de tamanhos de até 100 nm. Mas, o material obtido do recipiente de Si3N4 após 20 min de moagem apresentou uma maior porcentagem de partículas com diâmetros médios equivalentes entre 40 nm e 1000 nm, correspondente a 29%. / The Ti-Nb alloys are suitable for use in implants due to their high tensile strength and biocompatibility. One of the methods to obtain these alloys is the powder metallurgy, because it allowing to get pieces closer to near-net-shape. Theories showing that the densification rate range conversely like a function of the grain size. The great interest in the manufacturing of nanostructured materials – NsM (particles smaller than 100 nm) is due to possibility to obtain a sintered material in a smaller time and in more low temperatures than conventional powders, with the best densification, because it is more reactive. In this work, after hydrogenation and use of higher energy ball milling by until 60 min, were obtained powders of titanium hydride and niobium hydride, with ultra-fine/nanometric structure, what help in the diffusion process during a later stage of sintered. Milling medium of different materials (stainless steel and silicon nitride - Si3N4) were used. Independently of the grinding medium used, the material obtained exhibit approximating 5% of the particles with the cumulative values of size until 100 nm. But, is the possible to verify that the material obtained of the Si3N4 vessel, after milling by 20 min, exhibited a greater percentage of particles with average equivalent diameters between 40 nm and 1000 nm, than correspond to 29%.

Islamic architecture is arguably one of the greatest manifestations of Islamic visual culture. One of the defining aspects of the unique, aesthetic richness of traditional Islamic architecture has been the application of ceramic ornamentation or embellishment. There is a growing concern, however, that this legacy is being eroded. The diminishing identity of Islamic visual culture is particularly evident through current architectural developments occurring in the Arab states. The building revolution in the Gulf countries has dramatically increased momentum since the onset of the ‗oil economy‘, echoing the phenomena of globalization. This research project explores these concerns, discussing the erosion of Islamic ‗identity‘ within contemporary architecture in the Gulf States and in particularly Kuwait, as well as the ensuing decline in the use of ceramics as a defining embellishment material. The research compares the aesthetics of traditional and contemporary Islamic architectural design, whilst also examining the reasons behind this erosion in traditional design style. The diminishing identity of Islamic visual culture is investigated by combining studies in the fields of art, aesthetics, design, architecture, and the social sciences, in order to understand the nature of the research problem. A series of case-studies demonstrates how ceramics may be used to re-introduce a sense of Islamic identity within contemporary architecture. This offers design proposals, new materials and technical processes that acknowledge the rich traditions of Islamic Ceramics while also being appropriate for application within the context of contemporary Islamic architecture detailing; blending contemporary aesthetics and technical thinking with traditional Islamic design. The aim of the case-studies is to offer proposals for a new aesthetic vocabulary of architectural embellishment that is both appropriate to and innovative within, the context of contemporary Islamic architecture. This new aesthetic vocabulary III specifically blends contemporary design principals, new materials and technical processes, whilst acknowledging the rich traditions of Islamic ceramics. The PhD project, applies two types of research methodology: theoretical research and practice-based research. The former focused on social sciences and applied quantitative and qualitative research approaches, including surveys and interviews undertaken within Kuwait. The findings obtained from these surveys verified the emergence of a new cultural style of contemporary architecture and shaped the practice-based element of the project; proposals for ceramic embellishment that are contemporary, while still reflecting many recognizable aspects of traditional Islamic design. The new architectural style can be attributed to factors such as globalization, the adoption of international building styles, and a seeming unwillingness to incorporate traditional styles into new building design, all of which contribute to the currently weak identity of Arabic / Islamic ceramics within Kuwait. Despite of this, the survey revealed that Kuwaiti society maintains a strong relationship and affiliation with Islamic culture, although many seemed unaware of their own rich culture and its past legacy. The practice-based research involved two distinct phases. The first phase involved the development of a large number (172) of new glazes. The glazes were intended to reflect the palette of colours used over generations of Islamic Ceramic culture, while still being appropriate for integration within the contemporary Islamic architectural environment. The second phase of practice involved a series of case studies, embracing a wide range of contemporary architectural ceramic design processes (including 2 and 3 Dimensional geometrical patterns and interpretations of contemporary calligraphic design). The case studies utilised a number of modern technologies, such as 3D Solid modelling, CNC Rapid Prototyping and Laser-cutting, to prove that modern design and manufacturing technologies can be integrated within traditional ceramic processes. The aim being to both provide ceramic products that architects and designers can use to enhance the modern IV architectural environment of Kuwait and re-establish the creative status of ceramics.

Doctor of Philosophy / Department of Plant Pathology / Bikram S. Gill / H13, a dominant resistance gene transferred from Aegilops tauschii into wheat (Triticum aestivum), confers a high level of antibiosis against a wide range of Hessian fly (HF, Mayetiola destructor) biotypes. Previously, H13 was mapped to the distal arm of chromosome 6DS, where it is flanked by markers Xcfd132 and Xgdm36. A mapping population of 1,368 F2 individuals derived from the cross: PI372129 (h13h13) / PI562619 (Molly, H13H13) was genotyped and H13 was flanked by Xcfd132 at 0.4cM and by Xgdm36 at 1.8cM. Screening of BAC-based physical maps of chromosome 6D of Chinese Spring wheat and Ae. tauschii coupled with high resolution genetic and Radiation Hybrid mapping identified nine candidate genes co-segregating with H13. Candidate gene validation was done on an EMS-mutagenized TILLING population of 2,296 M₃ lines in Molly. Twenty seeds per line were screened for susceptibility to the H13-virulent HF GP biotype. Sequencing of candidate genes from twenty-eight independent susceptible mutants identified three nonsense, and 24 missense mutants for CNL-1 whereas only silent and intronic mutations were found in other candidate genes. 5’ and 3’ RACE was performed to identify gene structure and CDS of CNL-1 from Molly (H13H13) and Newton (h13h13). Increased transcript levels were observed for H13 gene during incompatible interactions at larval feeding stages of GP biotype. The predicted coding sequence of H13 gene is 3,192 bp consisting of two exons with 618 bp 5’UTR and 2,260 bp 3’UTR. It translates into a protein of 1063 amino acids with an N-terminal Coiled-Coil (CC), a central Nucleotide-Binding adapter shared by APAF-1, plant R and CED-4 (NB-ARC) and a C-terminal Leucine-Rich Repeat (LRR) domain. Conserved domain analysis revealed shared domains in Molly and Newton, except for differences in sequence, organization and number of LRR repeat in Newton. Also, the presence of a transposable element towards the C terminal of h13 was indicative of interallelic recombination, recent tandem duplications and gene conversions in the CNL rich region near H13 locus. Comparative analysis of candidate genes in the H13 region indicated that gene duplications in CNL encoding genes during divergence of wheat and barley led to clustering and diversity. This diversity among CNL genes may have a role in defining differences in the recognition specificities of NB-LRR encoding genes. Allele mining for the H13 gene in the core collection of Ae. tauschii and hexaploid wheat cultivars identified different functional haplotypes. Screening of these haplotypes using different HF biotypes would help in the identification of the new sources of resistance to control evolving biotypes of HF. Cloning of H13 will provide perfect markers to breeders for HF resistance breeding programs. It will also provide an opportunity to study R-Avr interactions in the hitherto unexplored field of insect-host interaction.

Esta dissertação teve como objetivo principal o estudo da produção de peças pelo processo da metalurgia do pó que formaram liga metálica na fase de moagem dos pós metálicos. Para o desenvolvimento do estudo, optou-se pela utilização de pós metálicos de titânio e nióbio, pois a sua interação, reduz a temperatura de transformação da fase Ti- para Ti-, que por sua vez pode ser utilizada em implantes e sistemas de fixação óssea. As concentrações de massa das amostras produzidas por metalurgia do pó foram de 75%Ti/25%Nb e 50%Ti/50%Nb. Inicialmente as amostras foram processadas em um moinho atritor, a rotação de 200 rpm por 80 horas com atmosfera inerte, favorecendo a formação de soldas frias e por sua vez difusão entre as partículas. As misturas foram então compactadas em duas etapas, com a primeira em uma matriz rígida de ação simples e na segunda, com uma ferramenta por ação isostática, para se obter uma melhor densificação e boa resistência mecânica a verde da peça. A sinterização foi realizada em atmosfera inerte de argônio, através de um fluxo continuo do gás. O incremento da concentração do Nb na matriz do Ti afeta a difusão, estabilizando a fase- no processo de moagem, afetando também, as propriedades mecânicas, aumentando a resistência e reduzindo o módulo de elasticidade. As partículas de Nb reduziram os esforços gerados durante o desgaste e dificultaram a formação de camadas espessas de óxido atuando como barreira. / This thesis aims to study the production of parts by powdered metallurgy process that passed through alloy formation in the grinding phase of powdered metals. To develop this study, titanium and niobium powdered metals were chosen, once their interaction reduces the temperature that turns the Ti- phase to Ti-, which in turn can be used in implants and bone fixation systems. The mass concentrations of the samples produced by powdered metallurgy were 75%Ti/25%Nb and 50%Ti/50%Nb. Initially, the samples were processed in an attritor mill, with a rotation of 200 rpm for 80 hours in an inert atmosphere, favoring the formation of cold welds and diffusion between the particles. The mixtures were then compressed in two stages, with the first in a rigid matrix of simple action, and the second with a tool with isostatic action, in order to obtain a better densification and good mechanical strength of the green part. The sintering was performed in an inert atmosphere of argon, through a continuous flow of gas. The concentration increase Nb on the Ti matrix affects diffusion, stabilizing the phase on the milling process, also affecting the mechanical properties by increasing the strength and reducing the elastic modulus. The Nb particles reduced the stresses generated during the wear and hindered the formation of thick oxide layers acting as a barrier.

abstract: With the new age Internet of Things (IoT) revolution, there is a need to connect a wide range of devices with varying throughput and performance requirements. In this thesis, a wireless system is proposed which is targeted towards very low power, delay insensitive IoT applications with low throughput requirements. The low cost receivers for such devices will have very low complexity, consume very less power and hence will run for several years. Long Term Evolution (LTE) is a standard developed and administered by 3rd Generation Partnership Project (3GPP) for high speed wireless communications for mobile devices. As a part of Release 13, another standard called narrowband IoT (NB-IoT) was introduced by 3GPP to serve the needs of IoT applications with low throughput requirements. Working along similar lines, this thesis proposes yet another LTE based solution called very narrowband IoT (VNB-IoT), which further reduces the complexity and power consumption of the user equipment (UE) while maintaining the base station (BS) architecture as defined in NB-IoT. In the downlink operation, the transmitter of the proposed system uses the NB-IoT resource block with each subcarrier modulated with data symbols intended for a different user. On the receiver side, each UE locks to a particular subcarrier frequency instead of the entire resource block and operates as a single carrier receiver. On the uplink, the system uses a single-tone transmission as specified in the NB-IoT standard. Performance of the proposed system is analyzed in an additive white Gaussian noise (AWGN) channel followed by an analysis of the inter carrier interference (ICI). Relationship between the overall filter bandwidth and ICI is established towards the end. / Dissertation/Thesis / Masters Thesis Electrical Engineering 2017

Made available in DSpace on 2016-06-02T19:09:59Z (GMT). No. of bitstreams: 1 TeseJFRC.pdf: 4478992 bytes, checksum: 4f9821b5fc063c6231c9f93eaa83d7ab (MD5) Previous issue date: 2003-10-29 / Universidade Federal de Minas Gerais / In the present work, Mg based nanocomposites were developed in the following systems: Mg TM, MgH2 TM, MgH2 MgF2 e MgH2 TM MgF2 (where TM means transition metal). The nanocomposites were processed by high energy ball milling and the obtained powders were characterized by in-situ X-ray diffraction during heating, transmission and scanning electron microscopy and differential scanning calorimetry. The microstructural evolution during heating of the MgH2 + 5%at%Nb was monitored by in-situ X-ray diffraction. It was concluded that the NbH/MgH2 and Nb/MgH2 nanointerfaces play major role on the hydrogen adsorption. These nanointerfaces act as fast diffusion paths or diffusion short circuits. The contribution of the thermodynamic attraction of these interfaces on hydrogen and its influence on sorption are also discussed. Both thermodynamic and kinetic effects accelerated the hydrogen desorption by the Mg-Nb composite. Based on the above, a mechanism for hydrogen desorption by the Mg-Nb by the Mg-Nb nanocomposite was proposed. It was observed that MgF2 greatly improved the desorption kinetics of hydrogen in the MgH2-MgF2 nanocomposite, showing it catalytic effect. The best result concerning the hydrogen desorption kinetics was for the [MgH2]90[MgF2]10 (wt %) nanocomposite. The on set desorption temperature of this nanocomposite was 253ºC. It was concluded that hydrogen diffuses through the MgH2/MgF2 nanointerfaces (fast diffusion paths). In this way, the hydrogen desorption kinetics was improved by the action of these nanointerfaces. / Neste trabalho foram desenvolvidos nanocompósitos para armazenagem de hidrogênio dos sistemas: Mg MT, MgH2 MT, MgH2 MgF2 e MgH2 MT MgF2 (onde MT significa metal de transição). Todos os nanocompósitos foram processados por MAE (moagem de alta energia) e os pós obtidos tiveram suas características morfológicas, estruturais e de dessorção de H2 investigadas por meio das técnicas de difração de raios-X in situ durante o aquecimento da amostra, microscopia eletrônica de varredura e transmissão e calorimetria diferencial de varredura. A evolução microestrutural do nanocompósito MgH2 + 5%at.Nb foi analisada por difração de raios-X in situ durante aquecimento. Foi concluído que as nanointerfaces NbH/MgH2 e Nb/MgH2 agem como caminhos de alta difusão ou curto circuitos difusionais. Além disso, é discutida a termodinâmica do hidrogênio por essas interfaces. A melhoria nas características de dessorção de H2 no nanocompósito Mg-Nb é explicada tanto pelos fatores cinéticos quanto pelos termodinâmicos. A partir daí foi proposto um mecanismo que descreve a dessorção do sistema Mg-Nb. Nos compósitos à base de MgH2 MgF2 foi possível constatar a efetividade catalítica do MgF2 no MgH2. O melhor resultado de cinética de dessorção do hidrogênio foi obtido com o nanocompósito [MgH2]90[MgF2]10 (%em massa). A temperatura de inicio da decomposição do hidreto de Mg foi de 253ºC. Foi concluído que no nanocompósito MgH2-MgF2 o hidrogênio penetra através das nanointerfaces MgH2/MgF2 (caminhos de alta difusividade e livre de óxidos), assim promovendo a aceleração da cinética de dessorção do nanocompósito.

Resumo: As ligas Ti-Nb são apropriadas para uso em implantes devido a sua alta resistência e biocompatibilidade. Um dos métodos de obter estas ligas é a metalurgia do pó, pois ele permite obter peças próximas ao seu formato final. Teorias indicam que a razão de densificação varia inversamente como uma função do tamanho da partícula. O aumento de interesse na fabricação de materiais nanoestruturados (partículas menores que 100 nm) é devido à possibilidade de obter um material sinterizado em um tempo menor e em temperaturas mais baixas, com uma melhor densificação do que pós convencionais, pois é mais reativo. Neste trabalho, após hidrogenação e moagem de alta energia por até 60 min, obteve-se pós de hidreto de titânio e hidreto de nióbio, com estrutura ultrafina/nanométrica, que auxilia o processo de difusão numa posterior etapa de sinterização. Meios de moagem de diferentes materiais (aço inoxidável e nitreto de silício - Si3N4) foram usados. Independentemente dos meios de moagem usados, o material obtido apresentou aproximadamente 5% das partículas com valores cumulativos de tamanhos de até 100 nm. Mas, o material obtido do recipiente de Si3N4 após 20 min de moagem apresentou uma maior porcentagem de partículas com diâmetros médios equivalentes entre 40 nm e 1000 nm, correspondente a 29%. / Abstract: The Ti-Nb alloys are suitable for use in implants due to their high tensile strength and biocompatibility. One of the methods to obtain these alloys is the powder metallurgy, because it allowing to get pieces closer to near-net-shape. Theories showing that the densification rate range conversely like a function of the grain size. The great interest in the manufacturing of nanostructured materials - NsM (particles smaller than 100 nm) is due to possibility to obtain a sintered material in a smaller time and in more low temperatures than conventional powders, with the best densification, because it is more reactive. In this work, after hydrogenation and use of higher energy ball milling by until 60 min, were obtained powders of titanium hydride and niobium hydride, with ultra-fine/nanometric structure, what help in the diffusion process during a later stage of sintered. Milling medium of different materials (stainless steel and silicon nitride - Si3N4) were used. Independently of the grinding medium used, the material obtained exhibit approximating 5% of the particles with the cumulative values of size until 100 nm. But, is the possible to verify that the material obtained of the Si3N4 vessel, after milling by 20 min, exhibited a greater percentage of particles with average equivalent diameters between 40 nm and 1000 nm, than correspond to 29%. / Orientador: Tomaz Manabu Hashimoto / Coorientador: Carlos Alberto Alves Cairo / Banca: Antonio Jorge Abdalla / Banca: Alfeu Saraiva Ramos / Mestre

Submitted by Automa??o e Estat?stica (sst@bczm.ufrn.br) on 2018-03-12T13:28:19Z No. of bitstreams: 1 RenanSavioDeAlmeidaCoelho_DISSERT.pdf: 6989070 bytes, checksum: 02ffff122848bc43e7d1a9ef1bef5171 (MD5) / Approved for entry into archive by Arlan Eloi Leite Silva (eloihistoriador@yahoo.com.br) on 2018-03-14T19:12:58Z (GMT) No. of bitstreams: 1 RenanSavioDeAlmeidaCoelho_DISSERT.pdf: 6989070 bytes, checksum: 02ffff122848bc43e7d1a9ef1bef5171 (MD5) / Made available in DSpace on 2018-03-14T19:12:58Z (GMT). No. of bitstreams: 1 RenanSavioDeAlmeidaCoelho_DISSERT.pdf: 6989070 bytes, checksum: 02ffff122848bc43e7d1a9ef1bef5171 (MD5) Previous issue date: 2017-07-28 / As propriedades ?nicas do comp?sito de matriz met?lica de cobre (Cu) refor?ada por dispers?o de part?culas de carboneto de tungst?nio (WC) s?o de grande import?ncia para v?rias aplica??es industriais, devido a sua excelente resist?ncia sob alta temperatura, boa resist?ncia ? corros?o e ? fratura. O comp?sito Cu-WC ? quimicamente e termicamente est?vel, al?m de possuir excelentes propriedades de condutividade t?rmica e el?trica. Tais caracter?sticas o tornam um promissor material para fabrica??o de contato el?trico de alta pot?ncia, eletrodos para soldagem, condutores de campo magn?tico pulsado, dispositivos de gerenciamento t?rmico e el?trico. Este trabalho investiga o efeito da moagem de alta energia na densifica??o e microestrutura dos comp?sitos WC-20%Cu e WC-18%Cu-2%Nb, bem como a influ?ncia da adi??o do ni?bio como inibidor de crescimento de gr?o. O efeito da press?o de compacta??o e da temperatura de sinteriza??o dos p?s preparados por moagem e mistura mec?nica na densidade tamb?m foram estudados. P?s de WC, Cu e Nb, na raz?o de 80, 20 e 2 por cento em massa, respectivamente, foram preparados por moagem e, tamb?m, por mistura mec?nica. A moagem dos p?s comp?sitos foi realizada a seco sob atmosfera ambiente com um recipiente e bolas de metal duro em um moinho attritor. Os p?s foram mo?dos a 900 rpm durante 90 minutos e sob uma raz?o de massa p? para bolas de 1:100. Compactos de p?s com forma cil?ndricas foram prensados a 200, 400 e 600 MPa em uma matriz de a?o uniaxial de 8 mm de di?metro. Os corpos verdes foram sinterizados nas temperaturas de 1030 ?C e 1150 ?C por 60 min. em forno tubular resistivo sob atmosfera de nitrog?nio. A microestrutura dos corpos sinterizados foi analisada por microscopia eletr?nica de varredura. Para analisar a presen?a de impurezas nos p?s elementares e mo?dos, an?lises qu?micas de FRX e EDS foram realizadas. A an?lise de DRX foi usada para detectar as fases presentes. Uma significativa diminui??o dos cristalinos e amorfiza??o das fases Cu e WC foi exibida pelos p?s mo?dos. Assim como, um menor tamanho de gr?o foi alcan?ado pelas microestruturas sinterizadas dos p?s comp?sitos Cu-WC com adi??o de Nb. Os compactos de p?s submetidos a maior press?o de compacta??o e temperatura de sinteriza??o tamb?m alcan?aram as maiores densifica??es. / The unique properties of copper metal matrix composite reinforced by dispersion tungsten carbide particles (WC) are of great importance for several industrial applications, due to their excellent high temperature strength and good corrosion and fracture resistance. This composite is chemically and thermally very stable at high temperatures, as well as having excellent thermal and electrical conductivity properties. These promising features make for the manufacture of high-power electrical contact parts, welding electrodes, magnetic field conductors, thermal and electrical management devices. This work investigates the effect of high energy milling on the densification and microstructure of the composites WC-20% Cu and WC-18% Cu-2% Nb as well as an influence of the addition of niobium as a grain growth inhibitor. The effect of the compacting pressure and the sintering temperature of the powders prepared by milling and mechanical mixing in the density were also studied. WC, Cu and Nb powders in the ratio of 80, 20 and 2 percent by mass, respectively, were prepared by milling and also mechanical mixing. The powder mixture were mechanically alloyed in a attritor ball mil in a dry environment. The powders were milled at 900 rpm, with a mass to powder ratio of 1: 100 balls for 1.5 hours, and pressed at 200, 400 and 600 MPa in a uniaxial matrix with 8mm diameter. The green bodies were sintered at temperatures of 1030 ?C and 1150 ? C for 60 min in a resistive tubular oven under a nitrogen atmosphere. A microstructure of sintered bodies for analysis by scanning electron microscopy. To analyze a presence of impurities in the initial powder and the as-milled powders, chemical analyzes of XRF and EDS were performed. A XRD analysis was used to detect as structure of crystalline. Amortization of the Cu and WC phases occurred, with a decrease in the crystalline phase due to milling, and inhibition of grain growth, both at temperatures, in the samples with Nb. Higher compaction pressure and higher sintering temperature show better results for densification of the material.

Esta dissertação teve como objetivo principal o estudo da produção de peças pelo processo da metalurgia do pó que formaram liga metálica na fase de moagem dos pós metálicos. Para o desenvolvimento do estudo, optou-se pela utilização de pós metálicos de titânio e nióbio, pois a sua interação, reduz a temperatura de transformação da fase Ti- para Ti-, que por sua vez pode ser utilizada em implantes e sistemas de fixação óssea. As concentrações de massa das amostras produzidas por metalurgia do pó foram de 75%Ti/25%Nb e 50%Ti/50%Nb. Inicialmente as amostras foram processadas em um moinho atritor, a rotação de 200 rpm por 80 horas com atmosfera inerte, favorecendo a formação de soldas frias e por sua vez difusão entre as partículas. As misturas foram então compactadas em duas etapas, com a primeira em uma matriz rígida de ação simples e na segunda, com uma ferramenta por ação isostática, para se obter uma melhor densificação e boa resistência mecânica a verde da peça. A sinterização foi realizada em atmosfera inerte de argônio, através de um fluxo continuo do gás. O incremento da concentração do Nb na matriz do Ti afeta a difusão, estabilizando a fase- no processo de moagem, afetando também, as propriedades mecânicas, aumentando a resistência e reduzindo o módulo de elasticidade. As partículas de Nb reduziram os esforços gerados durante o desgaste e dificultaram a formação de camadas espessas de óxido atuando como barreira. / This thesis aims to study the production of parts by powdered metallurgy process that passed through alloy formation in the grinding phase of powdered metals. To develop this study, titanium and niobium powdered metals were chosen, once their interaction reduces the temperature that turns the Ti- phase to Ti-, which in turn can be used in implants and bone fixation systems. The mass concentrations of the samples produced by powdered metallurgy were 75%Ti/25%Nb and 50%Ti/50%Nb. Initially, the samples were processed in an attritor mill, with a rotation of 200 rpm for 80 hours in an inert atmosphere, favoring the formation of cold welds and diffusion between the particles. The mixtures were then compressed in two stages, with the first in a rigid matrix of simple action, and the second with a tool with isostatic action, in order to obtain a better densification and good mechanical strength of the green part. The sintering was performed in an inert atmosphere of argon, through a continuous flow of gas. The concentration increase Nb on the Ti matrix affects diffusion, stabilizing the phase on the milling process, also affecting the mechanical properties by increasing the strength and reducing the elastic modulus. The Nb particles reduced the stresses generated during the wear and hindered the formation of thick oxide layers acting as a barrier.

Aços de alta resistência e baixa liga (ARBL) têm sido bastante utilizados na fabricação de tubulações para o transporte de petróleo e gás. Entretanto, o uso destes materiais em meios com elevadas concentrações de H2S, denominados sour, tem resultado em falhas frequentes, devido à suscetibilidade destes materiais ao desenvolvimento do fenômeno de trincamento induzido pelo hidrogênio (Hydrogen Induced Cracking - HIC), assim como devido a problemas de corrosão. O desenvolvimento de diferentes processos tecnológicos para a produção de tubos de aços ARBL, tais como a laminação controlada e resfriamento acelerado, a adição de microligantes, assim como a diminuição do teor de enxofre, fósforo, carbono e manganês, tem levado à elaboração de materiais com propriedades mecânicas otimizadas, permitindo também um melhor controle da microestrutura. As perdas de dureza e resistência mecânica devidas à redução do teor de manganês, são compensadas pela adição de elementos como cromo e nióbio. Neste trabalho estão sendo comparadas a resistência à corrosão e os parâmetros de permeabilidade do hidrogênio de dois tubos de aço API 5L X65 e uma chapa API 5L X65, todos do tipo ARBL e com baixo manganês (0,27%) e alto nióbio (0,083% a 0,090%), na solução B da norma NACE, TM-0284 (2011). Para isto, foram realizados ensaios de potencial de circuito aberto (Open Circuit Potential - OCP), espectroscopia de impedância eletroquímica (Electrochemical Impedance Spectroscopy - EIS) e curvas de polarização potenciodinâmicas no eletrólito naturalmente aerado, desaerado e saturado com H2S. Os testes de permeabilidade do hidrogênio foram realizados com base na norma ASTM INTERNATIONAL G148 - 97, porém usando a célula modificada de DEVANATHAN e STACHURSKY (1962) e com H2S como veneno catódico. Os materiais foram caracterizados por microscopia óptica (MO), microscopia eletrônica de varredura (MEV) e espectroscopia de energia dispersiva de Raios-X (X-Ray Energy Dispersive Spectroscopy - EDS) antes e depois de testes de imersão nos diferentes eletrólitos. Caracterização dos produtos de corrosão por difração de raios-X (DRX) também foi realizada após imersão em meio saturado com H2S (sour). As análises por MO e MEV mostraram matrizes ferríticas para os três aços, com a presença de baixos teores do microconstituinte martensita/austenita (M/A), de perlita e com baixo nível de inclusões uniformemente distribuídas e com composições químicas semelhantes. Os resultados dos ensaios de corrosão mostraram que, para todos os meios investigados, o aço denominado como B apresentou a melhor resistência à corrosão, enquanto aquele denominado como C se mostrou o mais suscetível em todas as condições estudadas. Para os três aços, a resistência à corrosão apresentou a seguinte ordem crescente de acordo com o meio de exposição: meio saturado com H2S < meio naturalmente aerado < meios desaerados. Ensaios de OCP e EIS no meio saturado com H2S em um período de 24h mostraram que a resistência à corrosão aumenta com o tempo em razão da formação de uma camada de sulfeto de ferro, que, no entanto, se apresentou pouco aderente. Os resultados dos ensaios de permeação de hidrogênio mostraram que o aço denominado B, que apresentou maior resistência à corrosão em todos os meios e que não apresenta perlita em sua microestrutura, teve o maior valor de difusividade efetiva de hidrogênio, menor concentração de hidrogênio atômico na sub-superfície e menor quantidade de traps por unidade de volume. Quanto aos outros dois materiais, os resultados dos testes de permeabilidade ficaram em desacordo com os resultados da caracterização microestrutural e dos testes de resistência à corrosão, indicando que fatores diferentes dos detectados neste estudo são importantes para governar essas propriedades. / High strength low alloy (HSLA) steels have been widely used in the manufacture of pipelines for the transport of oil and gas. However, the application of these steels in media with high H2S concentrations, denominated sour, has resulted in frequent failures due to the susceptibility of these materials to the development of Hydrogen Induced Cracking (HIC) phenomena, as well as due to corrosion problems. The development of different technological processes for HSLA piping production, like controlled rolling and accelerated cooling, the addition of microalloying elements, as well as the reduction of the amounts of sulphur, phosphorus, carbon and manganese, has led to the development of materials with optimized mechanical properties, also allowing a better microstructural control. Hardness and mechanical resistance reduction due to the lowering of Mn content are compensated by niobium and chromium addition. In this work, the corrosion resistance and the hydrogen permeability parameters of two API 5L X65 steel tubes and an API 5L X65 plate, all HSLA type and with low manganese (0.27%) and high niobium (0.083% to 0.090%) contents, are compared in solution B of NACE standard TM-0284 (2011). For this, open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization curves were carried out in the naturally aerated, deaerated and H2S saturated electrolyte. Hydrogen permeability tests were performed based on ASTM INTERNATIONAL G148-97, but using a modified DEVANATHAN and STACHURSKY (1962) cell and with H2S as cathodic poison. The materials were characterized by means of optical microscopy (OM), scanning electron microscopy (SEM) and X-Ray Energy Dispersive Spectroscopy (EDS) prior and after immersion tests in the different electrolytes. Characterization of the corrosion products by X-ray diffraction (XRD) was also performed after immersion in the H2S-saturated (sour) medium. The OM and SEM characterization showed ferritic matrices for the three steels, with the presence of low levels of the martensite/austenite (M/A) microconstituent, perlite and with a low level of inclusions evenly distributed and with similar chemical compositions. The results of the corrosion tests showed that, for all investigated media, the steel denominated as B presented the best resistance to corrosion, whereas the one denominated as C showed to be the most susceptible in all the conditions studied. For the three steels, the corrosion resistance showed the following ascending order according to the exposure medium: H2S saturated < naturally aerated medium < deaerated media. OCP and EIS tests in the H2S-saturated medium in a period of 24 hours showed that the corrosion resistance increases over time due to the formation of an iron sulphide layer, which, however, presented little adhesion. The results of the hydrogen permeation tests showed that the steel denominated B, that presented greater corrosion resistance in all media and that does not present perlite in its microstructure, had the highest values of effective hydrogen diffusivity, the lowest concentration of atomic hydrogen in the subsurface and the smallest amount of traps per unit volume. Concerning the other two materials, the results of the permeability tests were at variance with the results of the microstructural characterization and corrosion resistance tests, indicating that factors other than those detected in this study are important to govern such properties.