Thesis (M. S.)--Materials Science and Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Cochran, Joe; Committee Member: Berczik, Doug; Committee Member: Sanders, Tom; Committee Member: Sandhage, Ken; Committee Member: Thadhani, Naresh.

Thesis (Ph. D.)--Ohio State University, 2005. / Available online via OhioLINK's ETD Center; full text release delayed at author's request until 2006 Nov 29

Made available in DSpace on 2014-10-09T12:53:58Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:09:28Z (GMT). No. of bitstreams: 0 / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP

Made available in DSpace on 2014-10-09T12:53:58Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:09:28Z (GMT). No. of bitstreams: 0 / Este trabalho tem como objetivo o desenvolvimento de um combustível nuclear de alta densidade e baixo enriquecimento com base na liga ?-UMo, para aplicações nas quais seja necessário desempenho satisfatório a altas temperaturas, considerando-se a sua utilização na forma de dispersão. Para tanto, partiu-se da análise dos resultados dos testes RERTR (sigla em inglês para \"Reduced Enrichment of Research and Test Reactors\") e de alguns trabalhos teóricos envolvendo a elaboração de ligas metaestáveis de ?-urânio. Uma adição ternária é proposta, com base em propriedades de ligas binárias e ternárias de urânio-molibdênio estudadas, e que teve como objetivos um aumento na estabilidade da fase gama do urânio e a facilidade na obtenção dos pós. Assim, as ligas de urânio-molibdênio foram preparadas com adições de Mo de 5 a 10% em peso, e adição de 1 e 3% de elemento ternário (o silício), sobre uma liga base binária de U7Mo. Em todas as fases do processo de preparação, as ligas foram caracterizadas pelas técnicas tradicionais, para determinação de suas propriedades estruturais e mecânicas. Para a elaboração de um processo para a obtenção de pós destas ligas, o seu comportamento sob atmosfera de hidrogênio foi estudado em equipamento de análise térmica e gravimétrica diferencial. Temperaturas variaram da ambiente a 1000oC, por tempos de 15 minutos a 16 horas. A validação destes resultados foi feita em escala semi-piloto, na qual quantidades de 10 a 50g de pós de algumas das ligas foram preparados, sob atmosfera estática de hidrogênio. Os estudos de compatibilidade foram conduzidos expondo-se as ligas à atmosfera de oxigênio e ao contato com alumínio, para a verificação de possíveis reações por meio de análise térmica diferencial. As ligas foram submetidas a aquecimento constante até temperatura de 1000oC, e seu desempenho foi avaliado quanto a maior resistência à reação. 6 Com base nestes resultados, observou-se que as adições ternárias aumentam as temperaturas para a oxidação das ligas e reação com alumínio frente aos binários ?UMo. Um conjunto de condições para hidretação das ligas e fabricação dos pós foi estabelecido, tanto mais restritivos em termos de tempo, temperatura e necessidade de pré-tratamentos quanto mais estável a estrutura ?. Com a adição de ternário em pequeno excesso e formação de fase intergranular, mostrou-se que um aumento na estabilidade não prejudica a formação dos pós. / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP

No description available.

The alloy Mo-3Si-1B (wt%) may have the fracture toughness and oxidation resistance required for use as jet turbine engine blades. Mo-3Si-1B (wt%) forms a three-phase mixture of and #945;-Moss, A15 (Mo3Si) and T2 (Mo5SiB2). It has been observed that at high-temperatures, the A15 and T2 intermetallics form a oxidation resistant borosilicate glass coating. To achieve the proper combination of mechanical and thermal properties, the material must have a molybdenum matrix with a fine dispersion of intermetallics to produce a continuous protective layer. In this project, reactive sintering of molybdenum, Si3N4 and BN powders was used to create a semi-continuous molybdenum matrix with a fine dispersion of the A15 and T2 intermetallics. Sintering of the materials was further enhanced by the use of submicron-sized reactants. X-ray diffraction analysis was used verify the desired phases were formed. It was determined that formation of the A15 intermetallic phases begins as low as 1200?nd formation of T2 begins at 1300? The reactions are complete by 1400? Samples with bulk densities as high as 95% of theoretical were produced. Scanning electron microscopy images reveal a microstructure with dispersed intermetallics in a semi-continuous molybdenum matrix with grain sizes on the order of 1-4 and #956;m. It was found that by varying parameters such as mixing method and heating rates, it is possible to engineer the final microstructure, changing the level of dispersion of the intermetallics and continuity of the matrix.

Out of the known refractory metals and alloys, molybdenum (Mo) and its alloys are very important due to their unique combination of properties which render them suitable for various applications. Owing to their good creep properties, minimum damage from neutron irradiation and good compatibility with the liquid alkali metals, molybdenum and its alloys are well suited candidates for structural components in the newly developed Compact High Temperature Reactor (CHTR). However, to fabricate components for structural application from molybdenum and its alloys, the processing response needs to be established. The present thesis is an attempt to address this issue in a more generic manner. The study have been specifically aimed to examine the hot deformation behaviour of molybdenum and two of its alloys (Mo-TZM and Mo-TZC) over a high temperature range, for obtaining stable microstructure with good mechanical properties. The thesis basically addresses the following (i) the thermos-mechanical response of the material with change in deformation conditions, and (ii) the evolution of microstructure during hot deformation, and identification of associated mechanisms. Chapter 1 of the thesis includes an introduction of the material system and alloys with a detailed survey of the literature on the deformation behaviour of refractory metals and alloys that are used as structural materials in nuclear reactors. More emphasis is given to molybdenum and two of its alloy Mo-TZM and Mo-TZC. Chapter 2 includes the detail of the experimental techniques and analysis procedures that are followed in the course of investigation. The hot deformation behaviour of molybdenum in temperature range 1400 - 1700°C and strain rate range 0.001 - 10.0s-1 is discussed in chapter 3. The stress - strain behaviour has been further analysed to obtain strain rate sensitivity maps. The micro-mechanisms operative in different deformation domain has been analysed extensively by Electron Back Scatter Diffraction (EBSD) technique. Different restoration processes which include dynamic recrystallization, recovery and grain growth have been identified in different domains of deformation conditions. Chapter 4 of this thesis is dedicated to the hot deformation behaviour of Mo-TZM alloy. Deformation behaviour was studied under identical conditions as molybdenum. Mo-TZM showed higher strain rate sensitivity and high temperature strength than molybdenum. Dynamic recovery is the most predominant mechanism in Mo-TZM alloy as revealed through the analysis of stress strain curve as well as EBSD based investigation. At higher temperature and strain rates dynamic recrystallization has also been observed. The effect of excess carbon which results in Mo-TZC alloy, deformation behaviour has been investigated in chapter 5. The analysis of stress – strain curves in this case indicates the predominance of dynamic recrystallization over a range of deformation conditions. The mechanism has been identified as particle simulated nucleation (PSN). The significant growth of the deformed grains is observed at the highest temperature of deformation. A comparison of deformation behaviour of alloying addition in molybdenum alloys has been discussed in chapter 6. The results of deformation behaviour of molybdenum and its alloys has been compared vis-a-vis with another similar class of alloys based on Niobium (Nb) and apparent similarities and differences in the deformation behaviour has also been discussed in chapter 6. Finally, the overall summary of the thesis has been presented in chapter 7.

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Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 170-176).