Submitted by Fernanda Rodrigues de Lima (fernanda.rlima@ufpe.br) on 2018-08-28T22:32:40Z No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) TESE Roseana Florentino Pereira.pdf: 5029115 bytes, checksum: 567d2593b0716a916a10f59de192c44d (MD5) / Approved for entry into archive by Alice Araujo (alice.caraujo@ufpe.br) on 2018-09-06T22:58:01Z (GMT) No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) TESE Roseana Florentino Pereira.pdf: 5029115 bytes, checksum: 567d2593b0716a916a10f59de192c44d (MD5) / Made available in DSpace on 2018-09-06T22:58:01Z (GMT). No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) TESE Roseana Florentino Pereira.pdf: 5029115 bytes, checksum: 567d2593b0716a916a10f59de192c44d (MD5) Previous issue date: 2017-07-27 / No presente trabalho, revestimentos nanocompósitos de Ni-Co/SiC foram desenvolvidos por codeposição de nanopartículas de SiC em um banho eletrolítico com níquel e cobalto, utilizando o aço API 5L X80 como substrato. A influência da densidade de corrente catódica nas propriedades dos depósitos foi investigada e correlacionada com a eficiência de corrente. A morfologia e composição química da superfície e secção transversal dos revestimentos foi analisada por microscopia eletrônica de varredura acoplada com energia dispersiva de raios-X (MEV-EDS) e relacionadas aos resultados de microdureza Vickers (HV) e difração de raios-X (DRX). A adesividade foi verificada pela indentação Rockwell C. Medidas de potencial de circuito aberto (PCA), curvas de polarização potenciodinâmica (PP) e espectroscopia de impedância eletroquímica (EIE) foram realizadas em solução de NaCl 3,5% para investigar a resistência à corrosão. Os resultados mostraram que os revestimentos obtidos possuem morfologia de grãos ramificados em forma de agulha, com valores de microdureza mais elevados do que a microdureza do aço carbono e estrutura de fase cúbica de face centrada com orientação preferencial do plano (220). Através da análise da secção transversal dos depósitos, verificou-se que os mesmos eram formados por camadas intermediárias com composições e microdurezas distintas, de acordo com a densidade de corrente catódica aplicada. Os revestimentos nanocompósitos de Ni-Co/SiC deslocaram o potencial de corrosão para valores mais nobres e aumentaram a resistência à polarização, que resultou em taxas de corrosão mais baixas quando comparadas ao aço API 5L X80 sem revestimento. O revestimento obtido na condição de 55 mA/cm² obteve as melhores propriedades de resistência à corrosão e o estudo cinético realizado nesta corrente revelou que a formação do revestimento ocorre através da depositação de camadas com caráter autocatalítico. / In the present work, Ni-Co / SiC nanocomposite coatings were developed by codepositioning of SiC nanoparticles in an electrolytic bath with nickel and cobalt using API 5L X80 steel as substrate. The influence of cathodic current density on deposit properties was investigated and correlated with current efficiency. The morphology and chemical composition of the surface and cross-section of the coatings was analyzed by scanning electron microscopy coupled with X-ray dispersive energy (SEM-EDS) and related to the results of Vickers microhardness (HV) and X-ray diffraction (XRD ). The adhesiveness was verified by the Rockwell C indentation. Open circuit potential (PCA) measurements, potentiodynamic polarization curves (PP) and electrochemical impedance spectroscopy (EIS) were performed in a 3.5% NaCl solution to investigate corrosion resistance . The results showed that the coatings obtained have a needle shaped branched grain morphology, with microhardness values higher than the carbon steel microhardness and a cubic face structure with a preferred orientation of the plane 220. Through the cross-sectional analysis of the deposits, it was found that they were formed by intermediary layers with different compositions and microhardness, according to the applied cathodic current density. Ni-Co / SiC nanocomposite coatings shifted corrosion potential to nobler values and increased bias resistance, which resulted in lower corrosion rates when compared to uncoated API 5L X80 steel. The coating obtained under the condition of 55 mA / cm 2 obtained the best corrosion resistance properties and the kinetic study carried out in this chain revealed that the formation of the coating occurs through the deposition of layers with an autocatalytic character.

Orientadores: Edson Moschim, Oscar Ferreira de Lima / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-10T22:58:29Z (GMT). No. of bitstreams: 1 Vieira_KleberBetini_M.pdf: 5146160 bytes, checksum: 696a41837ed744dda41722755ffb45c3 (MD5) Previous issue date: 2008 / Resumo: Desde a descoberta do fenômeno da supercondutividade no diboreto de magnésio (MgB2) no ano 2001, a dinâmica dos vórtices neste material tem sido muito estudada, pois este fenômeno pode causar a destruição do estado supercondutor. Este trabalho tem o objetivo de avaliar o impacto no aprisionamento dos vórtices e analisar o comportamento da densidade de corrente crítica (Jc) em amostras de MgB2 misturadas com nanopartículas de níquel (Ni) em várias proporções. As amostras foram preparadas no National Physical Laboratory (Índia). Os pós de Mg e B foram misturados em proporções estequiométricas e mantidos em uma atmosfera de argônio (Ar) por 5h a 800 ºC. Em seguida, foram misturadas as nanopartículas de Ni com 0,5%, 1%, 2%, 3% e 5% em relação à massa da amostra de MgB2. A seguir elas foram homogeneizadas, prensadas e sinterizadas. Foram realizadas medições, em um sistema PPMS (Physical Property Measurement System) da Quantum Design, do: a) momento magnético em função da temperatura, para a determinação da temperatura crítica Tc das amostras; e b) momento magnético DC em função do campo magnético aplicado, para determinar o laço de histerese magnética das amostras. Com auxilio do Modelo de Bean foi determinada a corrente crítica Jc. Através de técnicas de mapeamento por imagem foram analisados: a) os domínios magnéticos presentes na amostra, através das técnicas de Microscopia de Força Atômica e de Força Magnética (AFM/MFM); e b) a granulometria média e homogeneidade, pela técnica de Microscopia Eletrônica de Varredura com detecção de Energias dos Raios-X Dispersos (MEV-EDX). Com o auxílio da Difração de Raios-X (DRX) foi analisada a formação da matriz de MgB2 e sua alteração com as adições do Ni, a formação de novos compostos e a presença de contaminantes. Através do nosso estudo podemos observar que as nanopartículas de Ni causaram o aprisionamento dos vórtices de Abrikosov, gerando um aumento na densidade de corrente crítica do MgB2. Apesar de uma pequena fração de Ni ter sido dissolvido na estrutura cristalina do MgB2, a degradação da temperatura crítica causada não é relevante frente ao aumento de Jc / Abstract: Since the discovery of the phenomenon of superconductivity in magnesium diboride (MgB2) in the year 2001, the vortex dynamics in this material has been widely studied, because this phenomenon can cause the destruction of the superconducting state. This study intends to assess the impact on the pinning of vortex and the behavior of the critical current density (Jc) in samples of MgB2, mixed with nickel nanoparticles in many proportions. Samples were prepared at the National Physical Laboratory (India). The Mg and B powders were mixed in stoichiometric proportion and maintained in an atmosphere of argon (Ar) for 5h at 800 °C. Then, they were mixed with the Ni nanoparticles in fractions of 0.5%, 1%, 2%, 3% and 5% of the mass of the sample. After they were homogenized, pressed and sintered. The following measurements were performed in a PPMS (Physical Property Measurement System) of Quantum Design: a) magnetic moment as a function of temperature, for determining the critical temperature Tc of the samples, and b) DC magnetic moment as a function of applied magnetic field, to determine the magnetic hysteresis loop of the samples. Using the Bean Model the critical current (Jc) was determined. Through techniques of image mapping there were analyzed: a) the magnetic domains present in the sample, through the techniques of Atomic Force Microscopy, and Magnetic Force (AFM / MFM), and b) the average grain size and uniformity by the technique of Scanning Electron Microscopy with the detection of dispersive X-ray energies (SEM-EDX). With the aid of X-Rays Diffraction (DRX) there has been examined the formation of the matrix MgB2 and the effects of Ni additions, the formation of new compounds and the presence of contaminants. Through our study we could observe that the Ni nanoparticles of lead to the pinning of Abrikosov vortices, generating an increase in the critical current density of the MgB2. Despite a small fraction of Ni that was dissolved in the crystal structure of MgB2, the degradation of the critical temperature is not relevant in face of the Jc increase / Mestrado / Eletrônica, Microeletrônica e Optoeletrônica / Mestre em Engenharia Elétrica

Submitted by Divisão de Documentação/BC Biblioteca Central (ddbc@ufam.edu.br) on 2017-09-27T19:14:47Z No. of bitstreams: 2 Dissertação - Leonardo S. Oliveira.pdf: 12252504 bytes, checksum: 0e50a939b3de4c6ee29549c3e7da914c (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Approved for entry into archive by Divisão de Documentação/BC Biblioteca Central (ddbc@ufam.edu.br) on 2017-09-27T19:15:01Z (GMT) No. of bitstreams: 2 Dissertação - Leonardo S. Oliveira.pdf: 12252504 bytes, checksum: 0e50a939b3de4c6ee29549c3e7da914c (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Made available in DSpace on 2017-09-27T19:15:01Z (GMT). No. of bitstreams: 2 Dissertação - Leonardo S. Oliveira.pdf: 12252504 bytes, checksum: 0e50a939b3de4c6ee29549c3e7da914c (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2017-08-07 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / A blend of elemental powders of Ni, Ti, Ge in the nominal composition Ni33Ti33Ge34 was subjected to mechanical alloying for 84h20min. The evolution of its structural and thermal characteristics was investigated by X-ray diffraction (XRD), Rietveld method (RM) and differential scanning calorimetry (DSC). Indeed, the inclusion of defects caused by milling induced a number of structural changes. I just five minutes of synthesis, it was ascertained the nucleation of intermetallics with crystallites sizes in nanometric dimensions. The formation of multiple phases is assigned to the low formation energy of the formed compound, among them the ternary alloy NiTiGe of the space group Pnma. From 2h20min, the crystalline structures undergo a remarkable degree of amorphization, reaching its maximum in 34h20min. Subsequently, in 59h20min, the metastability of the amorphous component gives rise to the re-nucleation of NiGe and Ni2.74Ge2 phases, which minimizing its free energy. In addition to this, the mechanical crystallization led to the formation of the TiO2-II high pressure phase and the B19’-NiTi shape memory alloy. In sequence, the amorphous content grows again and, with the growth of the tetragonal TiO2 phase, in 84h20min, the system recrystallizes and the milling was stopped. Therefore, it is observed that the system under study experiences a succession of metastable equilibrium due to the milling. / Uma mistura de pós elementares de Ni, Ge e Ti na composição nominal Ni33Ti33Ge34 foi submetida a mechanical alloying (MA) por 84h20min. A evolução das suas características estruturais e térmicas foram investigadas por difração de raios-X (DRX), método de Rietveld (MR) e calorimetria diferencial de varredura (DSC). De fato, a inclusão de defeitos provocados pela moagem induziu uma série de modificações estruturais. Em apenas cinco minutos de síntese, foi observada a nucleação de intermetálicos com cristalitos de dimensões nanométricas. A formação de múltiplas fases é atribuída a baixas energia de formação dos compostos formados, dentre elas a liga ternária NiTiGe do grupo espacial Pnma. A partir de 2h20min, as estruturas cristalinas presentes sofrem um notável grau de amorfização, atingindo seu máximo em 34h20min. Posteriormente, em 59h20min, a metaestabilidade da componente amorfa dá origem a re-nucleação das fases NiGe e Ni2.74Ge2, minimizando sua energia livre. Além dessas, a cristalização mecânica conduziu a cristalização da fase de alta pressão TiO2-II e da liga de memória de forma B19’-NiTi. Na sequência, a fração amorfa volta a crescer e, com a cristalização da fase TiO2 tetragonal em 84h20min, sistema recristaliza e a moagem foi interrompida. Dessa forma, nota-se que o sistema em estudo sofre uma sucessão de equilíbrios metaestáveis em função da moagem.

AgÃncia Nacional do PetrÃleo / CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / A soldagem de revestimento com ligas à base de nÃquel constitui uma interessante opÃÃo para a construÃÃo e o reparo de equipamentos para aplicaÃÃes em ambiente de corrosÃo severa, permitindo alcanÃar as caracterÃsticas desejadas (resistÃncia à corrosÃo) com uma significativa reduÃÃo de custos. Neste contexto, alguns estudos indicam que o processo de soldagem TIG com alimentaÃÃo de arame pode ser uma boa opÃÃo, desde que os parÃmetros de soldagem sejam corretamente ajustados. O objetivo do presente trabalho foi avaliar e otimizar os principais parÃmetros de soldagem, bem como avaliar o comportamento metalÃrgico de revestimentos de ligas de nÃquel depositados pelo processo TIG com alimentaÃÃo de arame frio sobre chapas de aÃo C-Mn. TrÃs ligas à base de nÃquel foram avaliadas no presente estudo: AWS ER Ni-Cr-Mo 3; AWS ER Ni-Cr-Mo 4 e AWS ER Ni-Cr-Mo 14. As soldagens foram realizadas numa primeira anÃlise em simples deposiÃÃo e, posteriormente, na formaÃÃo de camadas de revestimento, variando diversos parÃmetros operacionais. A caracterizaÃÃo microestrutural consistiu de anÃlises de microscopia Ãtica, microscopia eletrÃnica de varredura (MEV) e de transmissÃo (MET), espectroscopia de raio-X dispersivo em energia (EDS), difraÃÃo de elÃtrons retroespalhados (EBSD) e difraÃÃo de raios-X (DRX). Ensaios de polarizaÃÃo eletroquÃmica e desgaste com roda de borracha foram realizados para avaliar a resistÃncia à corrosÃo e ao desgaste, respectivamente. Os resultados mostraram que o processo TIG com alimentaÃÃo automÃtica de arame frio demonstrou ser uma opÃÃo interessante para a soldagem de revestimentos de ligas de nÃquel, podendo depositar em apenas uma camada, revestimentos que alcanÃam nÃveis de diluiÃÃo inferiores ou muito prÃximos de 5%, caracterÃstica favorÃvel para garantir boas propriedades aos revestimentos. A microestrutura dos revestimentos depositados com a liga AWS ER Ni-Cr-Mo 3 foi constituÃda por uma matriz γ com fases secundÃrias ricas em Nb (fase Laves e carboneto/nitreto de Ti e Nb). Estruturas complexas constituÃdas por um nÃcleo de nitreto de titÃnio-niÃbio (TiNbN) e uma casca de carboneto de niÃbio (NbC) ou niÃbio-titÃnio (NbTiC) foram observadas. A microestrutura dos revestimentos depositados com as ligas AWS ER Ni-Cr-Mo 4 e AWS ER Ni-Cr-Mo 14 foi constituÃda por uma matriz γ e fases secundÃrias ricas em Mo (fases σ, P e μ). Foi identificado um empobrecimento de Mo ao redor dos precipitados ricos em Mo, tornando esta regiÃo susceptÃvel à corrosÃo. O ensaio de polarizaÃÃo eletroquÃmica nÃo se mostrou capaz de avaliar o comportamento dos revestimentos quanto à corrosÃo por pites. O baixo nÃvel de dureza da matriz associada com uma pequena fraÃÃo volumÃtrica e dimensÃo dos precipitados resultou numa baixa resistÃncia ao desgaste abrasivo. / The weld overlay with nickel-based alloys is an interesting alternative for the construction and repair of equipments for applications in severe corrosive medium, allowing reach the desirable characteristics (corrosion resistance) with a significant reduction of cost. In this context, the GTAW cold wire feed process can be a good option for overlay deposition, since the welding parameters are correctly adjusted. The main objective of the present work was to evaluate and to optimize the operational and metallurgical characteristics of nickel-based alloys weld overlays deposited by the GTAW cold wire feed on C-Mn steel plates. The nickelbased alloys AWS ER Ni-Cr-Mo 3; AWS ER Ni-Cr-Mo 4 and AWS ER Ni-Cr-Mo 14 were studied in the this work. The welds were performed initially in single weld bead and later in multipass to produce the coating, changing several operational parameters. The microstructure was investigated using light microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive of X-ray spectroscopy (EDS), electron backscattering diffraction (EBSD) and X-ray diffraction (XRD). Potentiodynamics polarization analysis and wheel rubber wear test were used to evaluate the corrosion and abrasive wear resistance, respectively. The results showed that the GTAW cold wire feed process demonstrated to be an interesting option for the weld overlay with nickel-base alloys, could deposit in just one layer, coatings with dilution levels inferior or very close to 5%, important characteristics to assure a good performance of the coatings. The microstructure of the coatings deposited with AWS ER NiCrMo-3 alloy was constituted by the γ-matrix and secondary phases Nb-rich (Laves phase and Nb-Ti carbide/nitrides). It was observed that the precipitates with cuboidal and cruciform morphologies are formed by a complex structure constituted by titanium-niobium nitride (TiNbN) as nucleus and niobium carbide (NbC) or niobium-titanium (NbTiC) carbide as shell. The microstructure of the coatings deposited with the AWS ER NiCrMo-4 and AWS ER NiCrMo-13 alloys were constituted by the γ-matrix and secondary phases Mo-rich (σ, P and μ phases). It was identified a Mo depletion around the precipitates rich in Mo, causing a drop in the corrosion resistance. The potentiodynamic polarization was not shown capable to evaluate the behavior of the coatings for the pitting corrosion. The low level of hardness of the matrix associated with a small volumetric fraction of secondary phases (hard precipitates) resulted in a low abrasive wear resistance.

As estruturas do tri(hidroximetil) amino metano complexado com cobre Cu(II), Cu[NH2C(COH3)3]2+H2O e do tri(hidroximetil)amino metano dopado com prata Ag(I), Ag[NH2C(COH3)3] foram determinados por difração de raios-x. O complexo contendo íons de cobre refinou até um R de 0.034 e foram encontradas as seguintes características principais: sistema cristalino monoclínico; grupo espacial C2/c, a=12.955(2)Å b=10.793(1)Å c=10.091(2)Å &#946=116.62° V=1261.3(6)޵ Z=4; xDc=1.694(2)g/cm-3; &#955(K&#945Mo)=0.71073Å das reflexões medidas 1441 tinham I&#62 3&#948 (I). O íon de cobre está coordenado por pares de átomos de oxigênio e nitrogênio os quais formam uma pirâmide de base quadrada, o oxigênio da molécula de água ocupa o outro vértice da pirâmide. A determinação dessa estrutura é utilizada na interpretação da formação de complexos de cobre com tri(hidroximetil) amino metano em função do pH. A estrutura do tri(hidroximetil) amino metano dopado com prata apresentou as seguintes características: sistema cristalino ortorrômbico; grupo espacial Pna21; a=7.800(2)Å b=8.810(3)Å c=8.850(2)Å V=608.85(4)޵ Dc=1.329g/cm-3; Dm=1.337g/cm-3; 435 reflexões com I&#62 3&#948 (I); R=0.13; o carbono central é coordenado tetraedricamente por três átomos de carbono do tri(hidroximetil) e um nitrogênio do grupo amino. As estruturas do tris dopado com níquel, e do tris dopado com zinco apresentam-se isomorfa com a estrutura do tris dopado com prata. / The crystal structures of the tri(hydroxymethyl) amine methane complexed with cooper Cu[NH2C(COH3)3]2+H2O and the silver Ag[NH2C(COH3)3] doped into the tri(hydroxymethyl) amine methane have been determined by x-ray diffraction. The complex involving Cu++ refined to final R-factor of 0.034, and the following main features were found: the crystal system is monoclinic and its space group is C2/c, a=12.955(2)Å b=10.793(1)Å c=10.091(2)Å &#946=116.62° V=1261.3(6)޵ Z=4; Dc=1.694(2)g/cm-3; &#955(K&#945Mo)=0.71073Å from measures done, 1441 had I&#62 3&#948 (I). The Cu++ is coordinated by couples of atoms of oxygen and nytrogen, which form a base of a quadrangular pyramid, the pyramid vertex is formed by the oxygen of the water molecule. The determination of this structure is used to interpret the rise of tri(hydroxymethyl) amine methane and complexed with Cooper varying the pH. The silver doped into the structures of tris(hydroxymethyl) amine methane presented the following features: crystal system is orthorrombic; space group is Pna21; a=7.800(2)Å b=8.810(3)Å c=8.850(2)Å V=608.85(4)޵ Dc=1.329 g/cm-3; Dm=1.337 g/cm-3; R=0.13; 435 reflections with I&#62 3&#948 (I) the central carbon is coordinated tetrahedrally by three atoms of carbon from tri(hydroxymethyl) and a nitrogen from the amine group.

Superfícies de silício (100) foram inicialmente pré-ativadas em uma solução diluída de ácido fluorídrico contendo PdCl2. Após essa etapa, filmes finos de Cu-Ni-P foram quimicamente depositados utilizando-se um banho químico contendo 15g/l NiSO4.6H2O; 0.2 g/l CuSO4.5H2O; 15 g/l Na2HPO2.H2O e 60 g/l Na3C6H5O7.2H2O na temperatura de 80ºC onde foi adicionado NH4OH até que o pH da solução atingisse 8,0. Foi observado que as porcentagens estequiométricas de Ni e Cu variaram substancialmente no intervalo de 1 a 3min, e se tornaram praticamente estáveis em 50% e 35%, respectivamente, quando o tempo de deposição foi superior a 3min. Além disso, a porcentagem de P permaneceu quase constante em torno de 17-18% para todos os tempos de deposição. A distribuição de alturas nas imagens FE-SEM resultou bimodal para tempos na faixa de 1 e 3min onde a predominância do modo de maior altura aumentou substancialmente para o tempo de 3min. Tal fato serviu para corroborar a evolução da morfologia superficial de grãos menores com diâmetros na faixa de 0,02 a 0,1µm, predominantemente compostos de Ni, para grãos maiores, na faixa de 0,1 a 0,3µm e predominantemente compostos de Cu. Após um recozimento a 100oC durante 10min em ambiente 20%O2+80%N2, observou-se uma mudança na morfologia superficial em que os aglomerados de fósforo (Po) desapareceram enquanto que os grãos que compunham a imagem não mudaram substancialmente de tamanho após o recozimento. Apesar do desaparecimento dos aglomerados, a concentração de fósforo ainda apresentou valor semelhante ao valor de antes do recozimento (~17-18%). As análises de difração de raios X (XRD) indicaram o aparecimento de um pico de difração alargado ao redor de 22,6º característico de óxido de fósforo (P2O5) com estrutura vítrea amorfa significando que o fósforo em estado puro foi transformado na sua forma oxidada. Por outro lado, picos substancialmente menos intensos de NiO, Ni3P e Si5P6O25 foram observados. Verificou-se também para os filmes recozidos em N2+O2 que a resistividade aumentou para todos os tempos de deposição e o poder termoelétrico medido resultou quase independente do tempo de deposição e, portanto, foi quase independente da espessura do filme para as diferentes temperaturas medidas na faixa de 40 a 120ºC. / Silicon surfaces (100) were initially pre-activated in a diluted hydrofluoric acid solution containing PdCl2. After this step, Cu-Ni-P thin films were chemically deposited using a chemical bath containing 15g/l NiSO4.6H2O; 0.2 g/l CuSO4.5H2O; 15 g/l Na2HPO2.H2O e 60 g/l Na3C6H5O7.2H2O at the temperature of 80°C where NH4OH was added until the pH of the solution reached 8.0. It was observed that the stoichiometric percentages of Ni and Cu varied substantially for deposition time in the range of 1 to 3min, and became practically invariant at 50% and 35%, respectively, when the deposition time was greater than 3min. In addition, the percentage of P remained almost constant at around 17-18% for all the deposition times. The distribution of heights in the FE-SEM images resulted bimodal for times in the range of 1 and 3min where the predominance of the higher average height mode increased substantially for the time of 3min. This fact allowed one to corroborate the superficial morphology passing from smaller grains with diameters in the range of 0.02 to 0.1µm, predominantly composed of Ni to larger grains in the range of 0.1 to 0.3µm with Cu predominant composition. After an annealing at 100°C for 10min in a 20%O2+80%N2 environment, the phosphorus (Po) agglomerates disappeared while the size of the grains did not change substantially after the annealing. Despite the disappearance of the agglomerates, the phosphorus concentration still remained unchanged (~ 17-18%). X-ray diffraction (XRD) analysis showed a broad diffraction peak around 22.6º, which is characteristic of an amorphous vitreous structure (P2O5). In addition, substantially less intense peaks showing small amounts of NiO, Ni3P and Si5P6O25 were observed. It was also verified for the N2+O2 annealed films that the resistivity increased for practically all the deposition times and the measured thermoelectric power was almost independent of the deposition time and, therefore, was also independent of the film thickness for the various temperatures in the range from 40 to 120ºC.

Orientador: Paulo Roberto Mei / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-12T11:09:37Z (GMT). No. of bitstreams: 1 Bubani_FrancodeCastro_M.pdf: 7334881 bytes, checksum: 9cc4f96ceff0972bc2552404b4ccee84 (MD5) Previous issue date: 2008 / Resumo: Os efeitos da adição de níquel e da temperatura em ligas ferro-cromo foram estudados. Sete ligas de base ferro, com 18% Cr e teores de níquel variando entre zero e 60%, foram utilizadas no estudo (0, 10, 20, 30, 40, 50 e 60% Ni). Foram realizados ensaios de tração em temperatura ambiente, 350 e 700 ºC; simulação por termodinâmica computacional; microscopia ótica no estado recozido, nas amostras de quick stop, após deformação a frio, a 350 e a 700 ºC; difração de raios X no estado recozido, após deformação a 350 e a 700 ºC; ensaio de dureza a quente a 100, 200, 300 e 400 ºC; ensaio de impacto Charpy em temperatura ambiente e a -196 ºC; e ensaio de quick stop; análise térmica por DTA; ensaios de dureza no estado recozido, nos cavacos obtidos em torneamento, após deformação a 350 e 700 ºC. Os resultados dos ensaios de tração a 350 ºC foram correlacionados com os dados obtidos por Marques (2007), visando relacionar propriedades mecânicas e usinabilidade. A tendência geral de redução da usinabilidade com o aumento do teor de níquel foi relacionada com o aumento da resistência mecânica e da ductilidade a quente, proporcionados pelo níquel. A alta usinabilidade observada na liga 30% Ni foi relacionada com a presença de inclusões com cálcio nesta liga, o que proporcionou ganhos muito expressivos em usinabilidade, mas sem prejudicar as propriedades mecânicas avaliadas. / Abstract: The effects of nickel addition and temperature in iron-chromium alloys have been studied. Seven iron-base alloys with 18% Cr and nickel content varying from zero to 60% were used in the study (0, 10, 20, 30, 40, 50 and 60% Ni). The alloys were submitted to tension tests at room temperature, 350 and 700 ºC; computational thermodynamics simulations; optical metallography observations in annealed state, after deformation at room temperature, 350 and 700 oC, and in quick stop samples; x-ray diffraction, annealed and after deformation at 350 and 700 ºC; hot hardness test at 100, 200, 300 and 400 ºC; Charpy impact tests at room temperature and at -196 ºC; quick stop test; differential thermal analysis tests; Vickers hardness tests: annealed, on chips, after deformation at 350 and 700 ºC. The results of the tension tests at 350 ºC were correlated with the data obtained by Marques (2007), aiming at reaching a relationship between mechanical properties and machinability. The general tendency of reduction in machinability with the increase of nickel content was related to the increase in mechanical strength and hot ductility provided by nickel. The high machinability observed in the 30% Ni alloy was related with the presence of calcium inclusions in this alloy, which allowed for significant gains in machinability, but without loss to the evaluated mechanical properties. / Mestrado / Materiais e Processos de Fabricação / Mestre em Engenharia Mecânica

Mainly two different morphologies of martensite can be obtained in steels depending on the amount of alloying elements. The first morphology, referred to as lath martensite, forms in low alloy, low carbon steels. It is, by far, the most extensively studied form of martensite due to its industrial applications. The second morphology of martensite, referred to as plate martensite, forms in highly alloyed and in high carbon steels and in particular in Fe-High Ni alloys. In this case, the transformation product is disc shaped and internally twinned. This morphology is the only form of martensite that has the potential to exhibit shape memory properties. It is therefore of great interest to understand the mechanisms of its formation. This is investigated in the present dissertation through the study of the martensitic transformation occurring in a Fe-30.5%Ni-0.155%C alloy. More precisely, the influence of stress and grain size on the crystallography of plate martensite is discussed in the general framework of the phenomenological theory of martensite crystallography. This theory allows associating a unique shape deformation to each orientational variant. In this way, the experimental observations carried out at different length scales by means of optical microscopy, EBSD and TEM can be used to infer the transformation path followed under different conditions. Firstly, the burst configurations of variants observed in coarse-grained austenite under stress free conditions are rationalized by considering the mechanical couplings between the variants. It is shown that self-accommodating and autocatalytic couplings are responsible for the formation of hierarchical configurations of variants. More precisely, the transformation is shown to occur through the alternate formation of perpendicular plate groups of variants. Self-accommodation is the dominant coupling between variants of the same plate group while autocatalytic couplings are responsible for the transfer of the transformation from one generation to the next. It is suggested that the plastic accommodation of the shape deformation plays a dominant role in propagating the transformation to a lower length scales. Secondly, the influence of a uniaxial stress state on the transformation is studied. It is seen experimentally that only the most favoured variants are systematically formed in coarse Cube grains while coarse non-Cube grains generally transform into plate groups of variants that are only moderately favoured by the stress. These observations are well explained by considering the interaction energy between the applied stress and the shape deformation associated with the transformation. Thirdly, the influence of the austenitic grain size on the transformation is also studied. A decrease in grain size is seen to decrease the martensite start temperature. For a grain size below about 10µm, the thermal transformation in liquid nitrogen is indeed suppressed in the present alloy. This observation is related to the increasing yield strength of austenite as the grain size is reduced. A noticeable change in the morphology of martensite also accompanies the decrease in grain size. Indeed, martensite forming in coarse-grained austenite is mostly lens shaped and partially twinned while it appears plate shaped and fully twinned in smaller grains. Furthermore, martensite forming in fine-grained austenite develops self-accommodating configurations suggesting that most of the transformation deformations are elastically accommodated in this case. This is believed to be related to the observance of a shape memory effect in the present alloy in its fine-grained condition. / Doctorat en Sciences de l'ingénieur et technologie / info:eu-repo/semantics/nonPublished

Abstract In this work the LCVD of copper and nickel from the precursor gases Cu(hfac)tmvs and Ni(CO)4 has been investigated. The in-house constructed LCVD system and processes and the practical utilisation of these in prototype integrated circuit edit work are described. The investigated process parameters include laser power, laser scan speed, precursor partial pressure and the effect of H2 and He carrier gases. The deposited metal conductor lines have been examined by LIMA, AFM, FIB secondary electron/ion micrography, and by electrical measurements. Furthermore, the study of experimental FIB circuit edit processes is carried out and discussed with particular emphasis on ion beam induced ESD damages. It is shown how the LCVD and FIB methods can be combined to create a novel method to carry out successfully circuit edit cases where both methods alone will fail. The combined FIB/LCVD- method is shown to be highly complementary and effective in practical circuit edit work in terms of reduced process time and improved yield. Circuit edit cases where both technologies are successfully used in a complementary way are presented. Selected examples of some special circuit edit cases include RF- circuit editing, a high resolution method for FIB-deposited tungsten conductor line resistance reduction and large area EMI shielding of IC surfaces. Based on the research it was possible for a formal workflow for the combined process to be developed and this approach was applied to 132 circuit edit cases with 85% yield. The combined method was applied to 30% of the total number of edit cases. Finally, the developed process and constructed system was commercialized.

Previous research indicates compositional variation of pentlandite [(Fe,Ni)9S8] and the effect this variation may have on the electrochemical behaviour of pentlandite is poorly understood. Pentlandite is the primary source of nickel and an important base metal sulfide (BMS) in the platinum industry. It hosts significant amounts of PGEs especially palladium and rhodium when compared to chalcopyrite and pyrrhotite. The aim of the project was to investigate the possible compositional variations of natural pentlandite and the effect of these variations on the electrochemical behavior thereof. To study possible compositional variations, single pentlandite particles - in the order of 100μm in size from flotation concentrates (PGM deposits) and massive samples (massive ore bodies) - from various sources were employed. Electron microprobe analysis indicated a compositional variation of the pentlandite particles hand-picked from the flotation concentrate samples. Variation was observed in the cobalt, iron and nickel content and this was independent of the deposit. A slight compositional variation was observed from the massive pentlandite samples. The effect the compositional variation may have on the electrochemical reactivity of pentlandite was investigated using electrochemical techniques, i.e. measurement of the polarisation resistance and mixed potential as well as performing linear anodic voltammetry, current density–transients and electrochemical impedance spectroscopy (i.e. capacitance). Poor electrochemical response of the pentlandite microelectrodes was observed. Pre–existing pores, deep pores, cracks and the brittle nature of pentlandite microelectrodes may have contributed to the poor electrochemical response of natural pentlandite particles hand-picked from the flotation concentrate. Slight compositional variations of the massive pentlandite sample influenced the electrochemical behaviour. In aerated solutions, iron enriched pentlandites were less reactive after progressive oxidation. The lower reactivity of the electrodes was a result of thick oxide films formed. This was illustrated by polarisation resistance and capacitance measurements. The lower reactivity of the electrodes was also related to the mechanism of the reduction of oxygen at oxidised passive electrode surfaces. It is however difficult to distinguish if the differences in the reactivity was a result of the Fe/Ni ratio or the influence of cobalt. Current density transients confirmed that the reactivity of a pentlandite electrode to be time dependent. The reactivity of the electrode decreased during oxidation. A variation in the electronic properties of the formed oxide film was observed. Slight compositional variation of pentlandite did not have a significant effect on the rest potential values as do changes in the type of sulfides (e.g. pyrite vs. pentlandite). This was confirmed by similar rest potential values of various pentlandite electrodes. The oxidation of synthetic pentlandite may be influenced by the chemical composition. In de-aerated solutions, anodic oxidation (as indicated by the linear anodic voltammogram) of synthetic pentlandite started at a potential lower than of the natural electrodes. In aerated solutions, the synthetic pentlandite was less reactive and formed thicker oxide films. Copyright / Dissertation (MEng)--University of Pretoria, 2010. / Materials Science and Metallurgical Engineering / unrestricted