No description available.

M.Ing. (Mechanical Engineering) / Titanium and its alloys have the potential to serve as a strategic economic driver of the South African economy. The manufacture and use of high strength, lightweight materials such as titanium alloys have become of great importance in the aerospace and biomedical industries over the past few decades. The manufacturing costs of titanium alloy components however, are considered high due to the poor machinability of the material. Furthermore, as with all metals during machining, surface residual stresses are induced into the material. These are of particular interest in the aerospace industry as they can be either detrimental or beneficial to the performance and fatigue life of materials. The aim of this investigation is therefore to examine the effect that machining parameters have on the magnitude, sign and distribution of residual stresses induced in Grade 4 and 5 titanium alloys during high performance machining (turning). The effect of these machining parameters is investigated by residual stress measurements conducted with X-ray diffraction and grain structure analysis of the machined surfaces by optical microscopy. Results show that cutting speed and depth of cut have a significant effect on the residual stresses. At low cutting speeds, the surface residual stresses are largely compressive, becoming more tensile with an increase in cutting speed. An increase in depth of cut also introduces more compressive residual stresses into the material. The microstructural analysis of the alloys shows that grain deformation decreases with an increase in cutting speed and cutting depth.

No description available.

Titanium alloys are widely used for aerospace and biomaterial applications since their high specific strength, and high corrosion resistivity. Besides these properties, titanium is an excellent biocompatible material widely used for internal body implants. Because the products have complex geometries in both applications, Additive Manufacturing (AM) methods have been recently applied for production. AM methods can process a direct 3-D shape of the final product, decrease total production time and cost. However, high residual stress of the final product limits the application of AM components, especially the ones that are exposed to cyclic loading. In the present study, the initial microstructures and impact toughness of Ti6Al4V processed by EBM and CMT, and CP:Ti processed by SLM were experimented. In addition to initial microstructure and impact toughness, their response to different heat treatments were examined. Gleeble® 3500 was used for rapid heat treatment process. The change of mechanical properties due to different heat treatments were monitored with impact tests. Phase transformation kinetics of CP:Ti and Ti6Al4V were investigated with a Differential Scanning Calorimeter at slow heating and cooling rates. Microstructure examination was done with a scanning electron microscope. EBSD data was used to analyze the microstructure behavior. It is observed that toughness of the samples that are produced by powder-based AM methods were improved. Overall, residual stress, strain values, and grain orientation are the key elements that affected impact toughness AM produced components.

Mechanical properties of Nb-Ti composite superconducting wires were tested at room temperature. The results were analysed using simple composite theory, the rule of mixtures. The objective is to predict the mechanical properties of Nb-Ti superconducting composite wires as a function of volume ratio and geometry of the components, the composite wire size and the effect of heat treatment at final drawing wire sizes. To understand the mechanical behaviors of the Nb-Ti composite, mechanical testing of the individual composite components, Nb-Ti filament and copper matrix, was performed, and the geometry of the composite was also studied. The results indicate that for the monofilamentary composite simple composite theory with two components, Nb-Ti filament and copper matrix, can be used as the prediction of the UTS of the composite. For the multifilamentary composite three components make up the composites; a high strength Nb-Ti fiber, a low strength, high ductility bulk copper matrix and a mid-strength (between the Nb-Ti fiber's and bulk copper matrix's) interfilamentary copper matrix. After heavy cold work the UTS of Nb-Ti filaments and bulk copper matrix in the composite saturate, while the UTS of the interfilamentary copper increases as the interfilamentary spacing decreases. The UTS of the interfilamentary copper matrix as a linear function of the reciprocal of interfilamentary spacing is found. The controlling parameters in the manufacturing which determine the mechanical properties of Nb-Ti composite superconducting wires include superconductor to composite ratio, UTS of the Nb-Ti filament and copper matrix, wire final drawing size, and geometry of the composite such as size and number of the filaments, interfilamentary spacing, volume fraction of fringe and core bulk copper in multifilamentary composites. / Graduation date: 1991

Ti-6Al-2Sn-4Zr-2Mo-0.1Si specimens were shaped by repeated cycles of heating (to 954 °C) and hammer or press forging followed by a solution anneal that varied from 968 to 998 °C. The coupons were originally extracted from billets forged below the beta trans us ( 1009 °C) and slow cooled to ambient temperature. Macroscopic and microstructural banding is observed in some forged and solution annealed coupons, that consists of regions of elongated primary alpha. More significant banding is observed subsequent to annealing at lower temperatures (968 °C), whereas much less microstructural banding is present after annealing at higher temperatures (998 °C). About the same level of banding is observed in hammer forged and press forged coupons. The observation of these bands is significant since they may lead to inhomogeneous mechanical properties. Specifically, at least some types of banding are reported to affect the high temperature creep properties of this alloy. The origin of these bands was therefore researched. Classically, banding in Ti-6242-0.1Si has been regarded as a result of adiabatic shear, chill zone formation or compositional inhomogeneity. High and low magnification metallography, electron microprobe analysis and microhardness tests were performed on forged and annealed specimens in this investigation. The composition inside the bands appears identical to that outside of the bands. The fraction of primary alpha is also found to be identical. The bands have higher microhardness. These results suggest that the bands are not related to composition gradients. The bands also do not appear to be a result of adiabatic shear or other localized deformation. The bands of this study appear to originate from the elongated primary alpha microstructure of the forged billet (from which test coupons were extracted). The deformation of the extracted coupon may be neither fully homogeneous nor sufficiently substantial and the coupon is only partly statically restored after a solution anneal. Areas not fully restored appear as "bands" with elongated primary alpha, that are remnant of the starting billet microstructure. Therefore, a source of banding in Ti-6242-0.1Si alloy, additional to the classic sources, is evident. This type of banding is likely removed by relatively high solution treatment temperatures and perhaps greater plastic deformation during forging. / Graduation date: 1992

Orientador: Carlos Roberto Grandini / Banca: Antonio Augusto Couto / Banca: José Eduardo Spinelli / Resumo: A busca dos materiais que possuam determinadas características e atendam certas funcionalidades e aplicações é motivo de pesquisa em Ciência de Materiais. Dentre os materiais metálicos com aplicações na indústria aeroespacial, indústria química e aplicações médicas, o titânio e suas ligas tem se destacado por atender a requisitos necessários para estas aplicações. Um sitema bastante estudado para aplicações como biomaterial é o de ligas binárias Ti-Mo. Neste trabalho foram preparadas ligas de titânio com concentração de molibdênio acima de 20% em peso, com o objetivo de analisar a microestrutura, as propriedades mecânicas e o comportamento do elemento intersticial oxigênio. As ligas Ti-25Mo e Ti-30Mo foram preparadas por meio de um forno a arco voltaico. Posteriormente, as ligas foram submetidas a um tratamento térmico de homogeneização e depois foram laminadas, recozidas, e submetidas a tratamentos térmicos em atmosfera de oxigênio com o intuito de variar a quantidade deste elemento. As ligas foram caracterizadas por análise química, espectroscopia por energia dispersiva (EDS), medidas de densidade, difração de raios X, com análise por Rietveld microscopias ópticas e eletrônica de varredura, microdureza e módulo de elasticidade. Os resultados indicam que as ligas possuem boa homegeneidade química e microestructural, possuindo estrutura cúbica de corpo centrado. As amostras de Ti30Mo possuem durezae maior módulo de elasticidade em relação a Ti-25Mo. A microdureza das ligas não foi afetada pelas variações de oxigênio, e sim pelas condições de processamento. O módulo de elasticidade não sofreu variação significativa com relação ao oxigênio e ao processamento / Abstract: The search for materials that possess certain characteristics and meet certain features and applications is a cause of research in materials science. Among the metallic materials with applications in the aerospace and chemical industry, and medical applications, titanium and its alloys deserve attention meet the necessary requirements for these applications. A quite studied system for applications such as biomaterial is the binary Ti-Mo. In this work, titanium alloys, were prepared with molybdenum concentration higher than20 wt%, with the purpose of analyzing the microstructure, mechanical properties and the behavior of interstitial oxygen. Ti-25Mo and Ti-30Mo alloys were prepared using ar-furnace in argon atmosphere. Later, the ingots were subjected to homogenization heat treatment and cold-work (rolling), new amnealing, and to heat treatments in oxygen atmosphere in order to vary the amount of this element. The samples were characterized by chemical analysis, energy-dispersive spectroscopy (EDS), density, x-ray diffraction with analysis by Rietveld method, optical and scanning electron microscopies, microhardness and elastic modulus. The results indicate that the alloys have good chemical and microstructural homogeneity, with body-centered cubic structure. Ti-30Mo samples have lower microhardness values and elastic modulus than Ti-25Mo alloy. The microhardness of the alloys was not affected by oxygen content variations, but by processing conditions. The elastic modulus was not affected by other oxygen presence or processing / Mestre

Made available in DSpace on 2014-06-11T19:30:19Z (GMT). No. of bitstreams: 0 Previous issue date: 2013-08-23Bitstream added on 2014-06-13T20:40:13Z : No. of bitstreams: 1 araujo_ro_me_bauru_prot.pdf: 4250387 bytes, checksum: 5bb5887f248cdf7e9028406718b61694 (MD5) / A busca dos materiais que possuam determinadas características e atendam certas funcionalidades e aplicações é motivo de pesquisa em Ciência de Materiais. Dentre os materiais metálicos com aplicações na indústria aeroespacial, indústria química e aplicações médicas, o titânio e suas ligas tem se destacado por atender a requisitos necessários para estas aplicações. Um sitema bastante estudado para aplicações como biomaterial é o de ligas binárias Ti-Mo. Neste trabalho foram preparadas ligas de titânio com concentração de molibdênio acima de 20% em peso, com o objetivo de analisar a microestrutura, as propriedades mecânicas e o comportamento do elemento intersticial oxigênio. As ligas Ti-25Mo e Ti-30Mo foram preparadas por meio de um forno a arco voltaico. Posteriormente, as ligas foram submetidas a um tratamento térmico de homogeneização e depois foram laminadas, recozidas, e submetidas a tratamentos térmicos em atmosfera de oxigênio com o intuito de variar a quantidade deste elemento. As ligas foram caracterizadas por análise química, espectroscopia por energia dispersiva (EDS), medidas de densidade, difração de raios X, com análise por Rietveld microscopias ópticas e eletrônica de varredura, microdureza e módulo de elasticidade. Os resultados indicam que as ligas possuem boa homegeneidade química e microestructural, possuindo estrutura cúbica de corpo centrado. As amostras de Ti30Mo possuem durezae maior módulo de elasticidade em relação a Ti-25Mo. A microdureza das ligas não foi afetada pelas variações de oxigênio, e sim pelas condições de processamento. O módulo de elasticidade não sofreu variação significativa com relação ao oxigênio e ao processamento / The search for materials that possess certain characteristics and meet certain features and applications is a cause of research in materials science. Among the metallic materials with applications in the aerospace and chemical industry, and medical applications, titanium and its alloys deserve attention meet the necessary requirements for these applications. A quite studied system for applications such as biomaterial is the binary Ti-Mo. In this work, titanium alloys, were prepared with molybdenum concentration higher than20 wt%, with the purpose of analyzing the microstructure, mechanical properties and the behavior of interstitial oxygen. Ti-25Mo and Ti-30Mo alloys were prepared using ar-furnace in argon atmosphere. Later, the ingots were subjected to homogenization heat treatment and cold-work (rolling), new amnealing, and to heat treatments in oxygen atmosphere in order to vary the amount of this element. The samples were characterized by chemical analysis, energy-dispersive spectroscopy (EDS), density, x-ray diffraction with analysis by Rietveld method, optical and scanning electron microscopies, microhardness and elastic modulus. The results indicate that the alloys have good chemical and microstructural homogeneity, with body-centered cubic structure. Ti-30Mo samples have lower microhardness values and elastic modulus than Ti-25Mo alloy. The microhardness of the alloys was not affected by oxygen content variations, but by processing conditions. The elastic modulus was not affected by other oxygen presence or processing

Metal matrix composites can produce mechanical and physical properties better than those of the monolithic metal. Titanium alloys are widely used matrix materials as they can offer outstanding specific strength, corrosion resistance and other advantages over its competitors, such as aluminium, magnesium and stainless steel. In past decades, titanium matrix composites served in broad areas, including aerospace, military, automobile and biomedical industries. In this project, a revised powder metallurgy method, which contains cold isostatic pressing and hot isostatic pressing, was adopted to refine the microstructure of monolithic titanium. It was also used to manufacture titanium matrix composites. TiH2 powder was selected as the starting material to form Ti matrix and the reinforcements were sub-micron and nano-metric TiB particles. Mechanical properties and microstructure of commercial titanium composites exhaust valves from Toyota Motor Corporation have been studied as the reference of properties of titanium composites manufactured in this project. It has been shown that tensile strength and hardness of exhaust valves increase about 30% than those of similar matrix titanium alloys. Examination on powder starting materials of this project was also carried out, especially the dehydrogenation process shown in the DSC result. Mechanical properties and microstructures of titanium matrix composites samples in this project, as related to the process parameter, have also been investigated. The density of these samples reached 96% of theoretical one but cracks were found through out the samples after sintering. Fast heating rates during the processing was suspected to have caused the crack formation, since the hydrogen release was too fast during dehydrogenation. Hardness testing of sintered samples was carried out and the value was comparable and even better than that of commercial exhaust valves and titanium composites in literature. Microstructure study shows that the size of reinforcements increased and the size of grains decreased as the increasing amount of TiB reinforcements. And this condition also resulted in the increasing amount of the acicular alpha structure.

Orientador: Rubens Caram Junior / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-23T09:33:56Z (GMT). No. of bitstreams: 1 Lopes_EderSocratesNajar_D.pdf: 9279894 bytes, checksum: a2ed77cd79f48134e7daf5bc705afb0e (MD5) Previous issue date: 2013 / Resumo: Ligas de Ti do tipo ? metaestável exibem comportamento singular no tocante à possibilidade de manipulação de seu comportamento mecânico. Nessas ligas, a rigidez pode ser alterada por meio do controle das fases presentes, o que permite que esses materiais sejam incluídos no seleto grupo dos materiais com gradientes funcionais (functionally graded materials - FGM). Neste trabalho, objetivou-se projetar, produzir, processar, caracterizar e aplicar ligas Ti-Nb com adições do elemento ? estabilizador de baixo custo Fe. As ligas foram produzidas por fusão a arco voltaico e submetidas a diversas condições de tratamento térmico, incluindo solubilização acima da temperatura ?-transus, resfriamento rápido até a temperatura ambiente e tratamentos térmicos de envelhecimento entre 260 °C e 400 °C. A caracterização envolveu calorimetria diferencial de varredura, difração de raios-X e dureza Vickers em alta temperatura, análises metalográficas e de módulo de elasticidade por técnicas acústicas, ensaios de tração e mapeamento de rigidez por meio de nanoindentação. Os resultados obtidos mostram a retenção completa da fase ? para a liga Ti-30Nb-3Fe solubilizada e resfriada rapidamente e permitem também, compreender a decomposição da fase martensita ?" e a nucleação das fases ? e ?. A adição do elemento Fe tornou a cinética de transformação de fases bem mais lenta, propiciando, sob algumas condições, a supressão da fase ?, que é conhecida por aumentar a dureza em detrimento da ductilidade. Tais resultados foram utilizados no estabelecimento de condições ideais de processamento que permitem obter componentes ortopédicos com rigidez gradual. Finalmente, o conhecimento adquiro foi usado na fabricação de placas e parafusos de osteossíntese a partir da liga Ti-30Nb-3Fe com gradientes de funcionalidade / Abstract: Metastable ? Ti alloys exhibit singular behavior regarding the possibility of manipulating their mechanical behavior. In these alloys, the stiffness can be changed by controlling phases, which allows these materials to be included in the select group of functionally graded materials (FGM). This study aimed to design, produce, process, characterize and apply Ti-Nb alloys with addition of Fe, an inexpensive ? stabilizing element. These alloys were produced by arc melting and subjected to different heat treatment conditions, including solution above the ?- transus temperature, quenching to room temperature and aging heat treatments between 260 °C and 400 °C. Characterization involved differential scanning calorimetry, X-ray diffraction and Vickers hardness at high temperature, metallographic analyzes, elastic modulus by acoustic techniques, tensile test and stiffness mapping via nanoindentation. The results obtained show complete retention of the ? phase in the Ti-30Nb-3Fe alloy after solution in the ? field and rapid cooling to room temperature and also allow understanding martensite ?" decomposition and nucleation of the ? and ? phases. It was found that Fe additions make the phase transformation kinetics much slower, providing, for some conditions, suppression of the ? phase precipitation, which is known to increase the hardness at the expense of ductility. These results were used to establish optimal processing conditions, resulting in orthopedic component with graded stiffness. Finally, the knowledge acquired was used in the manufacturing of osteosynthesis plates and screws with functionality graded from the Ti-30Nb-3Fe / Doutorado / Materiais e Processos de Fabricação / Doutor em Engenharia Mecânica