Thesis (M.S.)--West Virginia University, 2004 / Title from document title page. Document formatted into pages; contains vi, 30 p. : ill. (some col.) Includes abstract. Includes bibliographical references (p. 29-30).

Thesis (Ph. D.)--Materials Science and Engineering, Georgia Institute of Technology, 2006. / Tannenbaum, Rina, Committee Chair ; Rosario Gerhardt, Committee Member ; Hamid Garmestani, Committee Member ; Karl Jacob, Committee Member Vita. Includes bibliographical references.

Submitted by Maria Eneide de Souza Araujo (mearaujo@ipen.br) on 2015-02-20T17:59:50Z No. of bitstreams: 0 / Made available in DSpace on 2015-02-20T17:59:50Z (GMT). No. of bitstreams: 0 / Dissertação (Mestrado em Tecnologia Nuclear) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Submitted by Maria Eneide de Souza Araujo (mearaujo@ipen.br) on 2015-02-20T17:59:50Z No. of bitstreams: 0 / Made available in DSpace on 2015-02-20T17:59:50Z (GMT). No. of bitstreams: 0 / Este estudo foi desenvolvido no Instituto de Pesquisas Energéticas e Nucleares IPEN mais especificamente, no Centro de Ciência e Tecnologia dos Materiais CCTM com apoio da empresa Innovatech. Foram estudados tubos de Co-Cr (L605) usados para fabricação de stents coronarianos, aplicação esta que pede um comportamento mecânico específico e biocompatibilidade. Os tubos de CoCr (L605) podem ser adquiridos em duas condições de história térmica: Trabalhado a frio ou com encruamento ou recozido. O tubo recozido se não estiver em condições para a aplicação, dificilmente será possível atingi-las com um novo tratamento térmico. O tubo encruado abre possibilidades para acertar as condições de tratamento térmico e obter a condição ideal de comportamento mecânico, sem comprometer outros aspectos importantes para a aplicação como biocompatibilidade. Foi selecionado um tubo de CoCr (L605) encruado e com uma quantidade grande de precipitados para os testes, foram selecionadas três faixas de temperatura para o tratamento térmico de recozimento uma abaixo do ponto de solubilização (1000°C), uma dentro da temperatura (1175°C) e uma terceira, mais próxima do ponto de fusão alcançável pelo forno (1250°C). Em cada temperatura foram usados quatro períodos de exposição ao forno( 4, 7, 10 e 15 minutos) totalizando uma matriz com 12 condições de tratamento térmico. Em cada tratamento térmico foram incluídas amostras para ensaio de tração e metalografia. O objetivo deste trabalho é estudar os efeitos dos tratamentos térmicos no comportamento mecânico e na microestrutura do material afim de levantar critérios para determinar os melhores parâmetros de tratamento térmico para a aplicação. / Dissertação (Mestrado em Tecnologia Nuclear) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

As superligas à base de cobalto são bem conhecidas por sua excelente resistência ao desgaste. Muitas pesquisas reportadas na literatura abordam o comportamento do desgaste destas ligas, seja no desgaste por deslizamento, erosivo ou abrasivo. Não obstante, o desgaste microabrasivo destas ligas não tem sido muito investigado, apesar dos danos causados por este tipo de solicitação. O comportamento do desgaste microabrasivo de três superligas à base de cobalto: a) 48% Co, 29 %Cr, 19 % Fe; b) uma liga com composição química próxima à da liga comercial Tribaloy T400 (Co 56 %, Cr 8.5%, Mo 29% Si 3.3 %) e c) uma liga com composição próxima à da liga comercial Stellite 6 (Co 64%, Cr 24 %, W 4.2 %, C 2,3%) foram investigadas. Os ensaios de microabrasão foram conduzidos com três abrasivos SiO2, Al2O3, e SiC em suspensão em água destilada, com concentração de 0,1 g/cm3. A carga aplicada foi de 0,3 N, a velocidade angular 20 rpm e a distância total de deslizamento, 48 metros. A análise das superfícies desgastadas por microscopia óptica, eletrônica de varredura e por perfilometria de contato mostraram que o tamanho, forma e dureza dos abrasivos podem influenciar significativamente os coeficientes de desgaste. Os ensaios conduzidos com partículas abrasivas de SiC e Al2O3 apresentaram maiores coeficientes de desgaste que os conduzidos com partículas de SiO2. A Liga Co-Cr-Fe mostrou os maiores coeficientes de desgaste quando comparada com as demais ligas, devido à baixa fração volumétrica de partículas de segunda fase, duras, precipitadas em sua microestrutura. Durante os ensaios, as três ligas, ensaiadas com os três diferentes abrasivos, apresentaram coeficientes de desgaste crescentes com o aumento da dureza do abrasivo; observou-se uma variação linear dos coeficientes de desgaste com a razão entre a dureza do abrasivo (Ha) e a dureza composta da liga (Hs), com R2 = 0.74. O micromecanismo dominante em todos os ensaios foi o desgaste abrasivo a dois corpos (grooving wear). A liga com composição próxima à da liga comercial Tribaloy T400, contendo fases de Laves dispersas em sua microestrutura, apresentou uma transição de micromecanismo de desgaste dúctil para frágil, quando submetida a ensaios com partículas abrasivas de Al2O3. Assim sendo, o volume de material removido nesta liga foi ligeiramente maior que o observado no ensaio com partículas de SiC. Na liga contendo baixa fração volumétrica de partículas de segunda fase, com matriz constituída por Co (CFC), observou-se uma camada subsuperficial nanocristalina de aproximadamente 1 µm de espessura, severamente deformada, imediatamente abaixo da superfície desgastada. Concluiu-se que o desgaste microabrasivo induziu a recristalização a frio do material encruado, com formação de grãos equiaxiais de dimensões nanométricas. / Cobalt alloys are well known for their excellent wear resistance. Many investigations are reported in literature related to the behavior of erosive, abrasive or sliding wear of these alloys. Nevertheless, the micro-abrasive wear of these alloys has not been thoroughly investigated, despite the damage caused by this type of wear. The microabrasive wear behavior of three cobalt alloys: a) 48 wt.% Co, 29 wt.% Cr, 19 wt.% Fe; b) an alloy with chemical composition close to Tribaloy T400 (56 wt.% Co, 8.5 wt.% Cr, 29% wt. Mo, 3.3 wt. %Si) and c) an alloy with chemical composition close to Stellite 6 (64wt.% Co 24 wt.% Cr, 4.2 wt.% W, 2,3 wt.% C were investigated. The tests were carried out using three 0,1 g/cm3 slurries composed by SiO2, Al2O3, and SiC particles, in suspension in distilled water. The applied load was 0.3 N, the rotational speed 20 rpm and the total sliding distance 48 m. Analysis of the worn surfaces of the tested alloys by Optical Microscopy, Scanning Electron Microscopy and Contact Stylus Profilometry showed that abrasive size, shape and hardness could significantly influence the wear coefficients. The tests carried out with SiC and Al2O3 slurries resulted in greater wear rates than those carried out in SiO2 slurry. Stellite 250, showed the greatest wear coefficient, compared to the two other experimental alloys, due to a very low volume fraction of hard second phase particles in the microstructure. Wear coefficients decreased with increasing abrasive particles hardness. An approximate linear correlation with the ratio between the hardness of the abrasives (Ha) and the compound hardness of the alloys (Ha) with a correlation factor R2= 0.74. The dominant wear micromechanism observed in all tests was two-body abrasion (grooving wear). The modified T400 alloy, containing Laves phase showed a transition from ductile to brittle wear mechanisms when testing with alumina slurries. The worn volume was slightly greater than the one observed with SiC. A severely deformed nanocrystalline layer was identified, immediately below the worn surface. It was concluded that cold recrystallization of the work-hardened material occurred, with the formation of nano sized equiaxed grains.

To date there has been much work carried out in the field of surface science to gain a better understanding of the fundamentals of a wide range of catalytic systems and reactions. The central theme of this thesis relates to cobalt based Fischer-Tropsch synthesis (FTS) with particular focus on the structure, composition and surface chemistry of CoPd bimetallic systems and on the interaction of Co with oxide support materials. In the work described in this thesis MEIS and STM are used to examine the growth of Co on Pd{111} and to characterise the structure of CoPd alloys created by thermal treatment of thin Co films. MEIS investigations indicate that Co grows initially as an fcc overlayer, but beyond a few layers, a stacking fault exists resulting in hcp growth. On annealing between 550 and 700 K, a previously unreported ordered surface alloy is observed giving rise to a p(2 x 1) structure which is concluded to be the surface termination of an ordered CoPd bulk alloy. At higher annealing temperatures, long range Moiré structure is observed by STM which MEIS reveals to correspond to a Pd-rich alloy. MEIS is used to investigate adsorbate induced segregation effects at CoPd surfaces on Pd{111}. The adsorption of O2, CO, H2 and CO/H2 mixtures (syngas) were all examined on a range of bimetallic surfaces. Oxygen adsorption on CoPd alloys strongly segregates cobalt to the surface as a result of the facile oxidation reaction. The behaviour of the components of syngas was more complex with the most noticeable effects being observed on surfaces which were more defect rich. The growth, annealing behaviour and adsorption properties of Co particles on oxide and mixed oxide surfaces are examined using MEIS and TPD.

Please read the abstract in the section 00front of this document / Dissertation (MSc (Chemistry))--University of Pretoria, 2007. / Chemistry / unrestricted

The master thesis summarizes the critical situation of the lack of a cobalt used in different industry branches. Due to its increasing price, it will not be possible to use in existing applications. One of these applications is production of cobalt alloys where the replacement of this element is impossible. This type of material keeps mechanical properties at high temperature. However, a suitable choice of technology can achieve at least its savings. In the field of welding, the alloys are joined without any use of an additional material. The possible solution could be the use of hybrid technologies or electron beam. Verification of weldability of both methods was realised in experimental parts and evaluated by destructive methods. The investigation was performed on wear resistant alloy Stellite 6B.

No description available.

Nanoalloys are an exciting new class of materials in the growing field of nanotechnology. Nanoalloys consist of the nanoscale co-aggregation of two or more metals with a potential to form compositionally-ordered phases or superstructures that have properties unlike those of the individual metal clusters or of bulk alloys of the constituent metals. This research seizes the opportunity that the nanoscale domain has to offer, and focuses on the synthesis of iron and cobalt nanoalloys via the simultaneous decomposition of iron cobalt organometallic precursors in a stabilizing environment, accompanied by the thorough characterization of the resulting nanoclusters. Zero-valent FeCo nanoalloys may potentially have interesting uses as magnetic materials. Since these clusters have sizes less than the size of their magnetic domain, the clusters will exhibit single domain magnetism. This magnetism may be observed by the presence of chain structures of FeCo nanoclusters due to the alignment of their single magnetic domains. In order to create a near-atomically homogeneous nanoalloy without preferential aggregation of its metal atom constituents, no clustering and phase separation should take place. In the bulk, alloys of iron and cobalt phase separate over most of the compositional range. Conversely, at the nanoscale, it may be possible to synthesize nanoalloy structures that are not normally favorable at given compositions, by the manipulation of reaction kinetics. In order to produce an atomically mixed nanoalloy, the transformation reactions of the organometallic precursors should display similar kinetic features, i.e. similar reaction rates. Therefore, the reaction kinetics of all the species in the reaction must be similar to avoid competition between them. As a result, kinetic control of the individual transformation reaction rates of each species may be used to modulate the aggregation and phase separation of the different species, and consequently control cluster morphology. This work has provided the framework for the design of synthesis methods that enable the control of the structure of FeCo nanoalloys with careful attention to precursor decomposition kinetics and the correlation between reaction kinetics and nanoalloy morphology.