No description available.

<p>Aluminum-Silicon (Al-Si) alloys are often preferred in the die casting industry due to excellent castability, high strength, corrosion resistance and low cost. Commonly, iron (Fe) is alloyed with the alloys to prevent die soldering. However, the addition of Fe in most of Al-Si alloys leads to formation of the intermetallic β-AlFeSi. The β-AlFeSi is harmful to the alloy structural integrity due to its needle-like morphology that creates stress concentration at the microscopic level. The phase presence is unfavorable to the mechanical properties and significantly reduces the elongation of the alloys. This research attempted to find viable way to control the morphology and formation of the β-AlFeSi phase.</p> <p>Thermodynamic simulations were done to investigate the sequence of intermetallic formation and other phases at different alloy compositions. The analysis of solidification paths of different alloys provided the correlation between the phase formation sequence and the fraction of the β-AlFeSi phase. The analysis also identified the feasible region of alloy design for minimizing the β-AlFeSi formation. Based on the thermodynamics simulation analysis, five alloys of different compositions were designed to validate the finding of the simulation. </p> <p>The tensile test results of the alloys indicated that lowering the Fe content increases the elongation of the alloy. The results also showed that elongation was reduced with the increase of Si level due to the formation of eutectic Silicon. The change of both Fe and Mn did not significantly affect the mechanical property of the alloy when the ratio of Fe to Mn was constant. Microscopic analysis showed that lowering the Fe level had effectively altered the morphology of the β-AlFeSi needle like structure. The β-AlFeSi was found to be smaller in terms of size when Fe is lower, subsequently reducing the probability of β-AlFeSi phase to be stress riser and crack initiation. </p> <p>The influence of heat treatment to the mechanical property of the alloys was also studied. The mechanical result on the heat-treated samples indicated that heat treatment is a viable method to improve the elongation property of the alloy. Microscopic observations showed that the β-AlFeSi phase was broken into shorter structures over the solution heat treatment process, resulting in better elongation. </p>

Submitted by Caio Castanho Xavier null (caiounesp@yahoo.com.br) on 2017-03-29T19:19:39Z No. of bitstreams: 1 Dissertação_versãofinal - Caio.pdf: 9229661 bytes, checksum: 257b6490f51832d9a3dc4786567f81c1 (MD5) / Approved for entry into archive by Luiz Galeffi (luizgaleffi@gmail.com) on 2017-03-30T18:09:19Z (GMT) No. of bitstreams: 1 xavier_cc_me_bauru.pdf: 9229661 bytes, checksum: 257b6490f51832d9a3dc4786567f81c1 (MD5) / Made available in DSpace on 2017-03-30T18:09:19Z (GMT). No. of bitstreams: 1 xavier_cc_me_bauru.pdf: 9229661 bytes, checksum: 257b6490f51832d9a3dc4786567f81c1 (MD5) Previous issue date: 2017-03-02 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O titânio, e as ligas baseadas nesse elemento, são amplamente utilizados como biomateriais, com aplicações tanto como implantes dentários quanto ortopédicos. Para isso, apresentam características importantes como: biocompatibilidade, resistência à corrosão, em geral baixo módulo de elasticidade e baixa densidade. O titânio possui uma temperatura de transformação alotrópica, que propicia o controle das propriedades da liga pela manipulação de sua microestrutura, através da adição de elementos de liga e/ou tratamentos térmicos. De fato, para ligas de titânio com uma composição definida, a realização de tratamentos térmicos, permite modificar a microestrutura da liga e, consequentemente, modificar as propriedades mecânicas do material em questão, fator essencial para o estudo em aplicações como um implante médico. O presente trabalho tem como objetivo o estudo detalhado de diferentes tipos de tratamentos térmicos de ligas do sistema Ti-Zr-Mo. Diferente de outros trabalhos da literatura, o estudo foi feito para cada tratamento térmico separadamente, analisando a microestrutura e a microdureza das ligas visando uma aplicação biomédica. Primeiramente, as ligas foram fundidas em um forno de fusão à arco voltaico, com quatro composições diferentes de liga: Ti-15Zr, Ti-15Zr-5Mo, Ti-15Zr-10Mo e Ti-15Zr-15Mo. Dessa maneira, pretendeu-se obter amostras com microestruturas de fase α, α+β e β. Através de uma análise por EDS, um estudo sobre a composição química das amostras foi realizado, sendo que, determinou-se que as ligas foram fundidas com uma boa qualidade e sem a presença de aglomerados ou segregados. A análise microestrutural foi realizada a partir de microscopias óptica e eletrônica de varredura. Para a liga Ti-15Zr, foi possível observar apenas a presença de uma estrutura acicular de fase α. Por outro lado, a liga Ti-15Zr-5Mo possui uma microestrutura de matriz β com finas agulhas de fase α nos contornos de grão. As ligas Ti-15Zr-10Mo e Ti-15Zr-15Mo apresentaram somente contorno de grão do tipo β. Para os tratamentos térmicos, houve um aumento de fase α nas condições tratadas por 600°C. No entanto, os tratamentos térmicos de 900°C e 1000°C demonstraram uma variação de fase na liga dependente do tipo de resfriamento realizado, onde o resfriamento lento obteve um crescimento de fase α. Através da análise da microdureza, percebe-se que em geral houve um aumento nos valores com o acréscimo de Mo e fase β na liga, sendo que, a liga Ti-15Zr apresentou uma microdureza entre 282-327 HV; a liga Ti-15Zr-5Mo de 331-390 HV; Ti-15Zr-10Mo apresentou valores entre 389-432 HV e a Ti15Zr-15Mo de 343-433 HV. / The element titanium and its alloys are widely used as biomaterials with applications in both dental implants as in orthopedics materials. Therefore, important features are required such as: biocompatibility, corrosion resistance, low values of Young modulus and low density. Also, titanium has an allotropic transformation temperature, which provides controlling the mechanical properties of the alloy. A microstructure manipulation can be achieved by the addition of certain alloying elements and heat treatments. In fact, for titanium alloys with a defined composition, heat treatments allow microstructure modification, hence alteration in the mechanical properties of the material, an essential subject for the study of medical implants applications. This study provides a detailed study of heat treatment conditions in a Ti-Zr-Mo system alloy. Unlike other papers in the literature, this study was done for each heat treatment separately, analyzing the microstructure and microhardness of the alloys for a biomedical application. First, the alloys were melted in an arc voltaic furnace, with four different alloys compositions: Ti-15Zr, Ti-15Zr-5Mo, Ti-15Zr-10Mo and Ti-15Zr-15Mo. In order to obtain samples with α, α+β and β phase microstructures. Through EDS analysis, a study on the chemical composition of the samples was performed. It was determined that the alloys were cast with good quality and without the presence of agglomerates or segregates. Microstructural analysis with optical microscopy and scanning electron was realized. For Ti-15Zr alloy, it was only possible to observe the presence of a lamellar structure composed of α phase. On the other hand, the Ti-15Zr-5Mo alloy has a microstructure of a β phase matrix with fine needle of α phases at the grain boundaries. The Ti-15Zr-10Mo and Ti-15Zr-15Mo alloys showed only beta type grain boundary. For the 600°C heat treatment conditions, it is noticed a growth in the α phase. However, for the 900°C and1000°C, there was a phase transition regarding the cooling rate of the heat treatment. The microhardness analysis shown that in general, microhardness increases with the Mo and β phase content of the alloy, where the Ti-15Zr alloy presented a microhardness (HV) between 282-327 HV; the Ti-15Zr-5Mo of 331-390 HV; the Ti-15Zr-10Mo showed values within 389-432 HV and the Ti15Zr-15Mo of 343-433 HV.

This dissertation presents the results of an investigation into the corrosion resistance of friction stir welding (FSW) for aerospace structures. Two of the most common aerospace aluminum alloys, 2024 and 7075, were investigated. In the as-welded condition, both alloys were found to be highly susceptible to exfoliation corrosion, and 7075 was found to be susceptible to stress corrosion cracking as well. The goal of this research was to identify proper initial temper selection and postweld aging treatments for enhancing the corrosion resistance of both 2024 and 7075 alloys, and their dissimilar joints. A large number of heat treatments were investigated for 7075 in the T6 and T73 tempers, including retrogression re-aging (RRA). Heat treatments were also investigated for 2024-T3 and 2024-T81. Samples were evaluated for resistance to exfoliation corrosion using optical microscopy. Microhardness, electrical conductivity, tension, and fatigue crack propagation tests were also performed on the samples. Beneficial heat treatments were found for both alloys as well as for their dissimilar joints. / "December 2005." / Thesis (Ph.D.)--Wichita State University, College of Engineering, Dept. of Mechanical Engineering

Made available in DSpace on 2014-10-09T12:31:46Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:01:06Z (GMT). No. of bitstreams: 1 12893.pdf: 1625501 bytes, checksum: fe39dd92498184bf046e7732940f5cc2 (MD5) / Dissertacao (Mestrado) / IEA/D / Escola Politecnica, Universidade de Sao Paulo - POLI/USP

Made available in DSpace on 2014-10-09T12:25:23Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:02:57Z (GMT). No. of bitstreams: 1 06047.pdf: 7935799 bytes, checksum: 59666d44ed8e3e6286af16eb865fb734 (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Made available in DSpace on 2014-10-09T12:35:20Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:06:11Z (GMT). No. of bitstreams: 0 / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Made available in DSpace on 2014-10-09T12:31:46Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:01:06Z (GMT). No. of bitstreams: 1 12893.pdf: 1625501 bytes, checksum: fe39dd92498184bf046e7732940f5cc2 (MD5) / Dissertacao (Mestrado) / IEA/D / Escola Politecnica, Universidade de Sao Paulo - POLI/USP

Made available in DSpace on 2014-10-09T12:25:23Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:02:57Z (GMT). No. of bitstreams: 1 06047.pdf: 7935799 bytes, checksum: 59666d44ed8e3e6286af16eb865fb734 (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Made available in DSpace on 2014-10-09T12:35:20Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:06:11Z (GMT). No. of bitstreams: 0 / O processo de conformação por spray é interessante devido à capacidade de conjugar, em apenas uma etapa do processo, a vantagem da técnica de solidificação rápida combinada com alta produtividade dos processos de fundição convencional. Este processo permite a obtenção de materiais livre de macrossegregações, livre de porosidades e com microestrutura refinada. A evolução recente das pesquisas está levando ao desenvolvimento de novas ligas e os resultados têm sido interessantes. O processo de solidificação rápida inerente da conformação por spray permite a produção de ligas com composições diferentes das obtidas pela fundição convencional. O objetivo deste trabalho foi o de caracterizar mecanicamente uma liga de alumínio AA-6082 conformada por spray. Os resultados de testes de dureza Vickers são apresentados para seções de um preformado em relação a sua altura (em um arranjo tridimensional). O material foi avaliado na condição como conformado por spray e após tratamento térmico de solubilização a 525 ºC por 1 h, seguido por envelhecimento a 125 ºC por períodos distintos de 1 h, 10 h, 100 h e 500 h. É mostrado que o a liga AA 6082 conformada por spray mostra uma boa estabilidade térmica em relação a variação da dureza durante o envelhecimento. / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP