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Characterization of nickel-niobium composite electrocoatings

FRATARI, Romulo Queiroz; ROBIN, Alain
Fonte: ASSOC BRASIL SOLDAGEM Publicador: ASSOC BRASIL SOLDAGEM
Tipo: Artigo de Revista Científica
POR
Relevância na Pesquisa
215.7924%
The electrodeposition of nickel based composites is been performed in order to improve properties of nickel layers, such as hardness, wear resistance, lubrication, corrosion resistance and catalytic activity. In the present work Nb powders (20 mu m average size) and Ni were codeposited on 1020 carbon steel by galvanostatic electrolysis of Watts bath, using 10, 20 and 40 mA/cm(2) cathodic current density and 240, 400 and 550 rpm electrolyte stirring rate. The morphology and texture of the coatings, Nb incorporated volume fraction, microhardness, adhesion to the substrate and corrosion behavior were evaluated. The Ni-Nb composite layers presented a rough morphology with randomly oriented Ni grains, whereas pure Ni coatings were smooth and showed highly preferred orientation in the [110] or [100] direction. The volume fraction of Nb in the composites determined by image analysis ranged from 8.5 to 19%. The 400 rpm stirring rate led to the highest Nb content (16 to 19016) for all current densities investigated The microhardness of the composite layers was higher than that of pure Ni coatings due to refining of Ni grains induced by incoporation of Nb particles. The adhesion of the coatings estimated qualitatively by bend test was found satisfactory. The Ni-Nb composites presented lower corrosion rate than Ni coatings in both 3% NaCl and 20% H2SO4 solutions.

Ion nitriding of a superaustenitic stainless steel: Wear and corrosion characterization

FERNANDES, F. A. P.; HECK, S. C.; PEREIRA, R. G.; PICON, C. A.; NASCENTE, P. A. P.; CASTELETTI, L. C.
Fonte: ELSEVIER SCIENCE SA Publicador: ELSEVIER SCIENCE SA
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
553.10984%
The superiority of superaustenitic stainless steel (SASS) lies in its good weldability and great resistance to stress corrosion and pitting, because of its higher chromium, molybdenum, and nitrogen contents, when compared to general stainless steels. However, some of its applications are limited by very poor wear behavior. Plasma-nitriding is a very effective treatment for producing wear resistant and hard surface layers on stainless steels without compromising the corrosion resistance. In this work, UNS S31254 SASS samples were plasma-nitrided at three different temperatures (400, 450, and 500 degrees C), under a pressure of 500 Pa, for 5 h, in order to verify the influence of the temperature on the morphology, wear, and corrosion behavior of the modified surface layers. The plasma-nitrided samples were analyzed by means of optical microscopy, micro-hardness. X-ray diffraction, wear, and corrosion tests. Wear tests were conducted in a fixed ball micro-wear machine and corrosion behavior was carried out in natural sea water by means of potentiodynamic polarization curves. For the sample which was plasma-nitrided at 400 degrees C, only the expanded austenite phase was observed, and for the treatments performed at 450 and 500 degrees C...

Effects of the high temperature plasma immersion ion implantation (PIII) of nitrogen in AISI H13 steel

da Silva, L. L. G.; Ueda, M.; Mello, C. B.; Codaro, E. N.; Lepienski, C. M.
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica Formato: 5989-5997
ENG
Relevância na Pesquisa
214.34734%
Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); In this paper we report the effect of high temperature PIII of nitrogen on the chemical and physical properties of AISI H13 steel. The implantation of H13 steels was carried out at different temperatures ranging between 300 degrees C and 720 degrees C. After the treatment, the surface morphology was drastically changed as observed by SEM analysis. Nitrogen penetration depth reaching up to 12 mu m was achieved at 620 degrees C and 720 degrees C. The maximum hardness of about 592 HV was obtained for the sample treated at 470 degrees C that is 17% higher than for untreated specimen. There was a decrease of the hardness values for temperatures above 470 degrees C. The same hardness behavior with the temperature was confirmed by nanoindentation testing. Although an enriched nitrogen layer was obtained, no evidence of nitride compounds was detected by XRD analyses. on the other hand, improvements of the H13 steel tribological properties and corrosion resistance were obtained. The wear tests were conducted by pin-on-disk tribometer (rotating mode). The wear volume decreased by factor of 4.5 compared to the standard tempered and annealed H13 steel and 2.6 times reduction of the coefficient of friction was achieved. The electrochemical measurements were performed in 3.5% NaCl solution...

Estudo da formação do cavaco no torneamento de superligas de níquel

Gama, Renann Pereira
Fonte: Universidade Estadual Paulista (UNESP) Publicador: Universidade Estadual Paulista (UNESP)
Tipo: Dissertação de Mestrado Formato: 128 f. il.
POR
Relevância na Pesquisa
215.43%
Pós-graduação em Engenharia Mecânica - FEG; O aumento das exigências mundiais por melhores produtos e a crescente competição entre empresas no mercado globalizado aumenta a busca por processos que garantam menores custos aliados a grande produtividade e produto de alta qualidade. Assim o grande desenvolvimento industrial e tecnológico tem aumentado a pesquisa em processos de usinagem que promovam, por exemplo, alto desempenho no que diz respeito à remoção de material, menor avaria e desgaste da ferramenta e menores impactos ao meio ambiente. Em relação às superligas a base de níquel, as mesmas têm um papel extremamente importante nas indústrias aeronáutica, automobilística, petróleo e gás dentre outras. As superligas a base de níquel estudadas foram a Nimonic 80A, o Inconel 718 e a Pyromet A31, materiais de difícil usinagem que possuem alta resistência mecânica e à corrosão em temperaturas elevadas. O objetivo deste trabalho é o estudo da formação do cavaco em relação aos diversos parâmetros de usinagem, a fim de alcançar alto desempenho e melhorias no torneamento cilíndrico externo destas ligas. As ligas foram torneadas utilizando-se diversos parâmetros de usinagem: velocidades de corte (75 e 90 m/min)...

Torneamento de liga de níquel Pyromet 31V (N07032) com ferramentas de metal duro

Bahia, André Luís Habib
Fonte: Universidade Estadual Paulista (UNESP) Publicador: Universidade Estadual Paulista (UNESP)
Tipo: Tese de Doutorado Formato: 158 f. : il.
POR
Relevância na Pesquisa
237.62543%
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); Pós-graduação em Engenharia Mecânica - FEG; Com a constante evolução tecnológica nas áreas aeronáutica, espacial, automobilística, dentre outras, o uso de materiais com elevadas resistência mecânica e à corrosão em altas temperaturas tem sido cada vez mais necessário. Dentre os materiais que atendem a estes requisitos em temperaturas até 815 ºC está a liga à base de níquel Pyromet® 31V (N07032). Esta liga é utilizada na confecção de válvulas de exaustão em motores diesel de alta potência nas quais é exigida, além de resistência a altas temperaturas, uma grande resistência à sulfetação, à corrosão e à fluência. Entretanto, devido à sua grande resistência mecânica e baixa condutividade térmica, ocorre uma concentração de calor principalmente na interface cavaco-ferramenta dificultando assim a sua usinabilidade. Este trabalho teve como objetivo estudar a usinabilidade da liga Pyromet® 31V nas condições laminada à quente (42 HRC) e seguida de solubilização e envelhecimento (37 HRC) utilizando-se ferramentas de metal duro com e sem recobrimento, com lubrificação abundante e com a técnica de MQF. Em termos de vida da ferramenta...

Degradação de materiais restauradores resinosos e do esmalte deciduo e permanente em soluções simuladoras da dieta; Degradation of resin-based restorative materials and deciduous and permanent enamel in food-simulating media

Gisele Maria Correr Nolasco
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 22/02/2007 PT
Relevância na Pesquisa
436.7835%
A cavidade bucal é considerada um ambiente agressivo onde a estrutura dentária e os materiais restauradores estão constantemente sujeitos a desafios térmicos, mecânicos e químicos. A associação destes fatores está diretamente relacionada à longevidade/estabilidade das restaurações, bem como à preservação da estrutura dentária. A exposição da estrutura dentária e dos materiais restauradores resinosos aos agentes da dieta pode causar erosão dental, amolecimento e aumento da rugosidade de restaurações resinosas, deixando-as mais susceptíveis ao desgaste. Dessa forma, os objetivos desta tese fundamentada em três capítulos foram: (1) avaliar o efeito do armazenamento em longo prazo em diferentes soluções simuladoras da dieta na rugosidade superficial de materiais restauradores resinosos; (2) avaliar o efeito da associação dos desafios erosivo e abrasivo no desgaste do esmalte decíduo e permanente; (3) avaliar o efeito da associação dos desafios corrosivo e abrasivo no desgaste de materiais restauradores resinosos. No capítulo 1, sessenta amostras de diferentes materiais restauradores (Filtek Z250, Esthet X, Filtek Flow, Dyract AP e Vitremer) foram armazenadas em 5 líquidos simuladores da dieta (água destilada...

Obtenção de nanocompósitos de alumina-zircônia para aplicação como biomaterial; Obtaining of alumina-zirconia nanocomposites for application as biomaterial

Katia Letícia da Silva
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 26/05/2011 PT
Relevância na Pesquisa
208.7354%
Cerâmicas de alumina de alta densidade e elevada pureza são usadas como biomateriais devido à combinação de excelente resistência à corrosão, boa biocompatibilidade, alta resistência ao desgaste e moderada resistência mecânica. Porém, a sua baixa tenacidade à fratura limita a sua gama de aplicações. Uma possibilidade para melhorar as propriedades destes materiais pode estar no uso de inclusões nanométricas de ZrO2 em matriz de Al2O3. O objetivo deste trabalho foi obter e caracterizar nanocompósitos de matriz cerâmica de alumina com inclusões nanométricas de zircônia, variando a quantidade, 5, 10, 15, 30 em volume de zircônia na alumina, visando melhorias nas propriedades mecânicas e de desgaste deste material e o uso do mesmo como biomaterial. Para isso, partículas nanométricas comerciais de ZrO2 foram adicionadas em matriz de alumina em diferentes proporções, utilizando moinho de bolas. As amostras de alumina pura e dos nanocompósitos de alumina-zircônia foram caracterizadas física, microestrutural e mecanicamente. Os resultados deste trabalho mostraram a eficiência do processo utilizado, obtendo uma boa dispersão das partículas de zircônia na matriz de alumina. A inclusão de até 15% de zircônia nanométrica na matriz de alumina promoveu um acréscimo nos valores de compressão diametral. Em relação aos valores de tenacidade à fratura...

Desenvolvimento de correlações entre microestruturas de solidificação e resistências ao desgaste e à corrosão; Development of correlations between solidification microstructures and wear and corrosion resistances

Emmanuelle Sá Freitas Feitosa
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 05/09/2013 PT
Relevância na Pesquisa
458.50297%
As ligas monotéticas à base de alumínio destacam-se por suas características tribológicas, principalmente as que se caracterizam pela fase minoritária (p. ex. bismuto, chumbo e índio) dispersa na matriz de alumínio, pois essas dispersões de elementos de baixas temperaturas de fusão e dureza, em função de suas propriedades autolubrificantes escoam facilmente em condições de deslizamento, resultando em um comportamento tribológico favorável. Já ligas hipoeutéticas Pb-Sb, mesmo as bem diluídas, possuem aplicações práticas bastante interessantes. Suas características estruturais e mecânicas, fazem com que o uso dessas ligas seja apropriado para a fabricação de conectores e grades positivas de baterias chumbo-ácido. Existe uma falta de estudos consistentes da evolução microestrutural de ligas monotéticas durante condições de solidificação transitória devidamente associada a propriedades de aplicação. Esse tipo de solidificação é de importância primordial, uma vez que engloba a maioria dos processos industriais envolvendo a transformação líquido/sólido. O presente estudo objetiva contribuir para o desenvolvimento de correlações entre microestruturas de solidificação e as resistências ao desgaste e à corrosão. Para o desenvolvimento do presente estudo...

Wear mechanisms in functionally graded aluminium matrix composites : effect of the lubrification by an aqueous solution

Gomes, J. R.; Ribeiro, A. R.; Vieira, A. C.; Miranda, A. S.; Rocha, L. A.
Fonte: Trans Tech Publications Publicador: Trans Tech Publications
Tipo: Artigo de Revista Científica
Publicado em //2005 ENG
Relevância na Pesquisa
437.3746%
Abstract. Functionally graded aluminium matrix composites reinforced with SiC particles are attractive materials for a broad range of engineering applications in the automotive, aircraft, sports, military and aerospace industries, whenever a superior combination of surface and bulk mechanical properties are required. In general, these materials are developed for the production of high wear resistant components. Also, often this kind of mechanical part operates in the presence of aggressive environments, such as marine atmospheres. In this work, aluminium composites with functionally graded properties, obtained by centrifugal cast, are characterised by reciprocating pin-on-plate sliding wear tests against nodular cast iron. Three different volume fractions of SiC reinforcing particles in each functionally graded material were considered. Sliding experiments were performed with and without the presence of a lubricant (3% NaCl aqueous solution). All tests were carried out at room temperature, under a normal load of 10N and constant frequency (1 Hz) and stroke (6 mm). In the case of the lubricated tests, electrochemical parameters (corrosion potential) were monitored during sliding. The worn surfaces as well as the wear debris were characterised by SEM/EDS. Friction values were in the order of 0.42 for unlubricated conditions...

Tribocorrosion behaviour of titanium in artificial saliva solutions

Vieira, A. C.; Ribeiro, A. R.; Rocha, L. A.; Celis, J. P.
Fonte: Universidade do Minho Publicador: Universidade do Minho
Tipo: Conferência ou Objeto de Conferência
Publicado em /09/2004 ENG
Relevância na Pesquisa
212.58232%
Dental implants are used to replace teeth lost due to decay, trauma or periodontal disease. In last years, the demand for such implants has increased exponentially due mostly to the ageing of the population and/or increased reliability of implant therapy. To choose a material for a particular rehabilitation treatment different characteristics must be considered such as mechanical strength, elastic properties, machinability, chemical resistance, etc. There is, however, one aspect that is always of prime importance; namely how the tissue at the implant site responds to the chemical disturbance imposed by the presence of a foreign material. In this work, commercially pure titanium (grade 2) was selected mainly due to its excellent corrosion behaviour and biocompatibility, that make this material one of the most used in dentistry. The tribocorrosion behaviour of the material in conditions simulating mastication, when in contact with artificial saliva solutions was investigated. Corundum was used as counterface material. The tests were performed, at MTM- KULeuven (Belgium), in a fretting machine specially adapted for tribocorrosion experiments. A normal load of 2 N was applied to the specimens and a displacement amplitude of 200µm at a frequency of 1 Hz. The number of cycles was varied between 5.000 and 10.000. In order to simulate different environmental conditions...

Tribocorrosion studies in centrifugally cast al-matrix siCp-reinforced functionally graded composites

Velhinho, A.; Botas, J. D.; Ariza, E.; Gomes, J. R.; Rocha, L. A.
Fonte: Trans. Tech. Publications Publicador: Trans. Tech. Publications
Tipo: Artigo de Revista Científica
Publicado em //2004 ENG
Relevância na Pesquisa
321.04195%
The present work reports results obtained from a series of preliminary experiments aiming at complementing the current knowledge about the wear behaviour of centrifugally-cast FGM Al/SiCp composites, through concurrent corrosion processes. Precursor MMC’s were prepared by rheocasting, using 118.8 µm SiC particles and an Al-10Si–2.2 Mg alloy. Those MMC’s were then molten and centrifugally cast in order to produce cylindrical FGMMC’s. Discs machined from the top surface of each sample were tested against nodular cast iron pins, using an inverted configuration pin-on-disc tribometer. Sliding tests took place at room temperature, over a 50000 m sliding distance, with a sliding speed of 0.3 m s-1, under a 5 N normal load; both dry-sliding and water-lubricated tests were performed. In order to elucidate the mechanisms involved, the wear coefficients were calculated for each condition, and the samples were subjected to morphological characterization via SEM/EDS. Concurrently, in the case of the water-lubrication tests, the corrosion potential of the tribological pair was monitored. The results obtained show an increase in material loss for the water-lubricated cases, although variations are registered depending on reinforcing particle volume fraction. At the same time...

TiCxOy thin films for decorative applications : tribocorrosion mechanisms and synergism

Mathew, M. T.; Ariza, E.; Rocha, L. A.; Fernandes, Ana C.; Vaz, F.
Fonte: Elsevier Publicador: Elsevier
Tipo: Pré-impressão
Publicado em 18/04/2008 ENG
Relevância na Pesquisa
647.40355%
Prova Tipográfica (In Press); Recently, tribocorrosion is widely accepted as an interdisciplinary area of research and such studies on various materials are gaining more attention by scientists and engineers due to its practical and economical significances in a wide range of applications. The main objective of the present work were to investigate the tribocorrosion behaviour of single layered titanium oxycarbide, TiCxOy, thin filmso on a reciprocating sliding tribometer, and in the presence of artificial sweat solution at room temperature, by considering the practical usage of such films as a decorative coating on various components. The films were produced by DC reactive magnetron sputtering, using C pellets incrusted in the Ti target erosion area. A gas atmosphere composed of Ar and O2 was used. The Ar flow was kept constant, and the oxygen gas flow varied from 0 to 10 sccm. During the wear tests both the open circuit potential and the corrosion current were monitored. Also, electrochemical impedance spectroscopy (EIS) tests were performed before and after sliding process. The modifications on the ‘‘native’’ coating microstructure and/or chemical composition induced by the variation of the deposition parameters were also evaluated and correlated with the wear–corrosion mechanisms occurring in each system. The corrosion studies...

TiCxOy thin films for decorative applications : tribocorrosion mechanisms and synergism

Mathew, M. T.; Ariza, E.; Rocha, L. A.; Fernandes, Ana C.; Vaz, F.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Publicado em /07/2008 ENG
Relevância na Pesquisa
646.54316%
Recently, tribocorrosion is widely accepted as an interdisciplinary area of research and such studies on the various materials is gaining more attention by the scientist and engineers due to its practical and economical significances. Hence the main objective of present work was to investigate the tribocorrosion behavior of single layered titanium oxycarbide, TiCxOy, thin films on a reciprocating sliding tribo-meter, and in the presence of artificial sweat solution at room temperature. Such films can be used as a decorative coating on various components. The films were produced by dc reactive magnetron sputtering, using C pellets incrusted in the Ti target erosion area. A gas atmosphere composed of Ar and O2 was used. The Ar flow was kept constant, and the oxygen gas flow varied from 0 to 10 sccm. During the wear tests both the open circuit potential and the corrosion current were monitored. Also, Electrochemical Impedance Spectroscopy (EIS) tests were performed before and after sliding in order to evaluate, in detail, the modification of the protective character of the coating introduced by the joint action of wear and corrosion. The modifications of the coating microstructure and/or chemical composition induced by the variation of the deposition parameters were also evaluated and correlated with the wear-corrosion mechanisms occurring in each system. The effect of hardness...

Influence of hydrogen peroxide on the tribocorrosion of titanium

Sequeiros, José Augusto Santos
Fonte: Universidade do Minho Publicador: Universidade do Minho
Tipo: Trabalho de Conclusão de Curso
Publicado em //2013 ENG
Relevância na Pesquisa
237.66531%
Disssertação de mestrado integrado em Engenharia Biomédica (área de especialização em Biomateriais, Reabilitação e Biomecânica); O titânio é um material vastamente utilizado na medicina dentária graças à sua excepcional biocompatibilidade e óptima resistência à corrosão. Mesmo assim, alguns dos implantes são rejeitados. Embora resistente à corrosão, o titânio não é completamente inerte em condições in vivo, existindo a libertação de partículas de desgaste e iões resultantes da sua corrosão. A complexidade do ambiente da cavidade oral, quer pelas suas propriedades químicas, electroquímicas ou mecânicas, é um excelente campo de estudo, que necessita de um conhecimento mais aprofundado para evitar perdas médicas ou económicas. O peróxido de hidrogénio é um composto químico comummente descrito como citotóxico para uma vasta gama de culturas animal, de plantas ou bacteriana. Este tem um papel preponderante na resposta imunitária dos seres vivos. Normalmente utilizado como agente de limpeza, em produtos de branqueamento de dentes ou para tratamento de feridas, o peróxido de hidrogénio está em constante contacto com tecidos, tornando-o um caso de estudo interessante na área biomédica. O principal objectivo deste trabalho prende-se com o estudo...

Effect of deposition current on microstructure and properties of CoCrWC alloy PTA coatings

Paes,R. M. G.; Scheid,A.
Fonte: Associação Brasileira de Soldagem Publicador: Associação Brasileira de Soldagem
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/09/2014 EN
Relevância na Pesquisa
314.9341%
Cobalt-Based alloys are largely applied to the surface of components as welded coatings. Carbides reinforced CoCrWC system is used to extend the service life under harsh environments involving wear and corrosion in different media. This work aims to evaluate the effect of deposition current on the microstructure and properties of PTA coatings. So, CoCrWC alloy (Stellite #6) was processed on AISI316L stainless steel plates with the following main arc current: 100, 120, 150, 180 and 200A. So, different interaction with the substrate must be expected and its effect on coatings features was evaluated. The geometry of single track coatings, dilution, formed phases and phase volume fraction was assessed by laser Confocal, scanning electron microscopy and X-ray diffraction analysis. Vickers hardness and wear tests were carried out to correlate microstructure to properties of coatings. Coatings showed microstructure composed by hypoeutectic dendrites of Cobalt solid solution and interdendrictic carbides. Dilution increased with deposition current from 11,8 e 56,5% which reduced the carbides fraction and increased the Cobalt solid solution areas, resulting in hardness decrease from 500 to 310HV0,5. Higher deposition current induced mass loss rate increase on pin-on-disc sliding wear tests...

The influence of microstructure on the corrosion and wear mechanisms of high chromium white irons in highly caustic solutions.

Nelson, G. D.
Fonte: Universidade de Adelaide Publicador: Universidade de Adelaide
Tipo: Tese de Doutorado
Publicado em //2010
Relevância na Pesquisa
478.3267%
High chromium white irons are used extensively for wear resistance applications and owing to their high chromium content are often used in erosive-corrosive environments such as alumina processing plants using the Bayer refining process. The first stages of the Bayer refining processes (the red side) involve the transfer of hot slurries containing a high proportion of erosive quartz particles suspended in a pH 14 caustic solution. The solution contains varying amounts of dissolved alumina making the environment erosive and corrosive. High chromium white irons are often used to prolong service life and reduce operating costs. Pump components are often cast high chromium white irons and piping is often weld overlayed with high chromium white iron. To date there has been very little information reported in the literature on the wear of high chromium white irons in alumina processing environments. Furthermore, very limited work has been reported on the corrosion behaviour of high chromium white irons in caustic environments. This thesis investigates the development of microstructure in high chromium white irons typically used in the Australian Alumina Industry and how variables such as the bulk chemical composition, cooling rate and heat treatment can be used to vary the microstructure. Microstructural characteristics that influence wear and corrosion were investigated by undertaking corrosion and erosion-corrosion wear tests in a sodium aluminate solution representative of what is found in the alumina processing industry. The corrosion of high chromium white irons in sodium hydroxide solution was compared with their corrosion in sodium aluminate solution to investigate the influence aluminate ions have on corrosion. A range of ex-service alumina processing plant high chromium white irons castings and weld overlays were investigated. This not only provided materials for further testing but from the examination of the wear surface allowed the results of laboratory wear tests to be compared with those of the plant samples and test methods validated. A total of four different commercially produced casting materials ranging from hypoeutectic to hypereutectic compositions were compared with an experimental high chromium white iron casting...

Oxidation and wet wear of silicon carbide; Oxidationsverhalten und nass-tribologisches Verhalten von Siliciumcarbid

Presser, Volker
Fonte: Universidade de Tubinga Publicador: Universidade de Tubinga
Tipo: Dissertação
DE_DE
Relevância na Pesquisa
441.2504%
Siliziumkarbid (SiC) ist sowohl die wohl bedeutendste Nichtoxidkeramik aber auch als Halbleiter ein vielversprechendes Material. Gaskorrosion in Gegenwart von Sauerstoff führt dabei als einzige feste Phase zu Bildung von SiO2 (passive Oxidation). Hierbei spielen jedoch viele Einflussfaktoren eine wichtige Rolle, wie zum Beispiel Porosität, Sinteradditive, Verunreinigungen, die kristallographische Orientierung, vorhergehende Oberflächenbehandlung und die chemische Zusammensetzung der oxidierenden Atmosphäre. Als Folge von Kristallisation verändert die zunächst glasartige SiO2-Schicht ihre Struktur und es kommt zur Ausbildung von runden Kristallisationszentren (Radialite). Diese Bereiche zeigen eine geringere Oxidationsrate, was auf langsamere Gasdiffusion zurückzuführen ist. Verunreinigungen, wie sie Beispielsweise in der Ofenatmosphäre vorkommen können, akkumulieren sich auf der Oberfläche der SiO2-Schicht und es kommt zu einer schmelzkatalysierten Rekristallisation als zweiter morphologischer Umwandlung der Oxidschicht. Schließlich bilden sich kleine kristalline Kugeln (Globulite). Das dazwischen befindliche Porenvolumen führt zu erhöhten Oxidationsraten. Die Gesamtkinetik der Oxidation ist somit potentiell komplex. Dennoch kann für die meisten SiC Materialvarianten ein allgemeines linear-parabolisch Zeitgesetz für den gesamten Oxidationsverlauf gefunden werden. Die ausgeprägte Anisotropie von SiC führt dazu...

An investigation into the wear and friction characteristics of ship propeller shaft and sea material combinations

Cornell, Robert L.; Lucas, Robert S.; Young, Harold L.
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado
EN_US
Relevância na Pesquisa
328.81926%
This thesis document was issued under the authority of another institution, not NPS. At the time it was written, a copy was added to the NPS Library collection for reasons not now known. It has been included in the digital archive for its historical value to NPS. Not believed to be a CIVINS (Civilian Institutions) title.; The unsatisfactory wear properties of various seal and propeller shaft material combinations on many of our submarines, particularly those of the deep-submergence class and those where the trend is towards the larger shaft diameters, prompted this investigation. While the fault may well lay in design, this paper approaches the problem as one in boundary lubrication; attempting to find the best combination of seal material and mating service in this particular service condition from a wear viewpoint. An additional aim was to attempt some correlation between wear, friction, and the physical properties involved. Results from this latter goal could well find application in the selection of steam turbine seals as well as those employed in the aircraft industry. The approach used by the authors was first to evaluate potential seal materials from different families in combination with various corrosion-resistant shaft materials. This work was done on the Kinetic Oiliness Testing Machine (KOTM) and the results are presented in Part I of this investigation. The testing involved obtaining friction and wear data on carbons and laminated phenolics...

Efecto del contenido de carbono sobre la resistencia al desgaste abrasivo de recubrimientos de CrC depositados por pulverización catódica magnetrón

Fonte: Fondo Editorial EIA Publicador: Fondo Editorial EIA
Tipo: Artigo de Revista Científica
Publicado em 05/11/2013 ES
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232.56824%
Los recubrimientos de carburo de cromo sobre acero son un buen candidato para aplicaciones de conformado y moldes de inyección. La alta resistencia mecánica, resistencia química y estabilidad a alta temperatura de la fase Cr3C2 pueden ser compatibles con el intenso desgaste abrasivo y la corrosión en tales operaciones de fabricación. En este trabajo se depositaron recubrimientos de CrC por pulverización catódica magnetrón RF, los cuales mostraron contenidos de carbono entre el 25 % y el 58 % por análisis EDS. Los valores de dureza de estos recubrimientos fueron entre 15 y 24 GPa; los más duros de las muestras tuvieron contenido de carbono en el rango de 39-53 %. El desgaste abrasivo de los recubrimientos se evaluó utilizando un equipo de disco abrasivo con polvo de diamante. El volumen de las huellas de abrasión se midió con las imágenes obtenidas en el microscopio interferométrico y además se corroboró con el cálculo del volumen geométrico basado en secciones medidas con el perfilómetro. El comportamiento al desgaste abrasivo mostró una marcada dependencia con el contenido de carbono. El desgaste abrasivo más bajo se obtuvo para los recubrimientos con el más alto contenido de carbono.; Chromium carbide coatings on steel are a good candidate for applications on forming and molding dies. The high mechanical strength...

Novel redesign of a pressure leach autoclave by a South African Platinum producer

Roux,J.O.; du Toit,M.; Shklaz,D.
Fonte: Journal of the Southern African Institute of Mining and Metallurgy Publicador: Journal of the Southern African Institute of Mining and Metallurgy
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/11/2009 EN
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The Impala Platinum Limited Base Metals Refinery in Springs, South Africa, refines convertor matte containing base metals and PGM's (platinum group metals) using a hydrometallurgical process. In addition to a PGM-rich concentrate that is further refined, the Base Metals Refinery produces nickel (in powder or briquette form), copper cathodes and cobalt powder. Five leaching stages are utilized to remove the base metals and impurities from the PGM concentrate. The project described in this paper involves a radical redesign of the second stage leach autoclave with the aim of reducing maintenance costs and downtime, increasing throughput and ensuring a safer working environment. The second stage leach process at the Base Metals Refinery, produces a PGM-rich residue through the extraction of copper and any remaining base metals from the first stage leach solid residue material. Leaching is performed in an autoclave operating at a pressure of 600 kPaG and a temperature of 140°C to 150°C. Concentrated H2SO4 is added to the feed to produce a solution with a free acid content between 10 and 30 g/L and a pH of less than 2. Oxygen is passed into the 1st and 2nd compartments of the autoclave. As a result of the aggressive, highly oxidizing conditions within the autoclave...