Orientador: Ana Paula Rosifini Alves Claro / Coorientador: Luiz Rogério de Oliveira Hein / Banca: Angelo Caporalli Filho / Banca: Maria Ismênia Sodero Toledo Farria / Resumo: Ligas de titânio são utilizadas para aplicações biomédicas devido as excelentes propriedades como a alta resistência à corrosão, biocompatibilidade e propriedades mecânicas. No presente trabalho, foram analisadas as microestruturase as propriedades mecânicas daliga Ti-30Ta e em amostras deformadas com diferentes graus de compressão. A liga foi obtida pela fusão dos metais puros em um forno a arcovoltaico com atmosfera inerte de argônio. O material obtido foi homogeneizado em um forno tubular a 1000 °C por 24 h e deformadas a friopelo processodeforjamento rotativo para obter barras de 13 mm de diâmetro. A liga foi avaliada utilizadastécnicas de difração de raios-X (DRX) em temperatura ambiente e com aquecimento, calorimetria diferencial de varredura(DSC), microscopia eletrônica de transmissão (TEM), microdureza e compressão de corpos de provas em diferentes graus de deformação. As amostras foram deformadas com taxas graus de 19%, 22% e 43% e analisadas, usando as técnicas de DRX,microscopia óptica, microdureza. A liga apresentou transformação alotrópica a uma temperatura próxima de 650°C, e microestrutura do tipo α', a deformação da amostra resultou em cisalhamento na amostra de 43%, as amostras apresentaram microdureza de 250, 269, 286 e 280HV para as amostras sem deformação, 19%, 22%e 43% de deformação / Abstract: Titanium and its alloys have been used for biomedical applications due their excellent properties, such as high corrosion resistance, biocompatibility and mechanical proprieties. In this work, the microstructure and mechanical proprieties of Ti-30Taand deformeds amples with different degrees of compression were analyzed The in gots were obtained in a arc melting furnace inan argon atmosphere. In gots were homogenized at 1000 ºCin a tubular furnace with argon atmosphere for 24 hours and than they were cold worked by swaging. and samples with 13 m mindiameter were obtained. The alloy was evaluated by X-raydiffraction (XRD), Heat treatment X ray diffraction (HTXRD)and differential scanning calorimetrical (DSC), transmission electron microscopy(TEM), micro hard nessand compression test with different deformations. The samples were forging at reductionratiosof 19%, 22% and 43%. After this deformation,its microstructure were evaluated by optical microscopy, X-ray diffraction(XRD)and micro hardness in each condition. The alloy show a allotropic transformation at 650 °C, and α' microstructure. The sample that was compressed with 43% shear and the others samples ( 19%, 22%) don't change their microstructure. the samples without deformation, 19%, 22% and 43% result 250, 269, 286, 280 HV / Mestre

Submitted by Luciana Ferreira (lucgeral@gmail.com) on 2018-04-24T11:46:58Z No. of bitstreams: 2 Dissertação - Ana Carolina Da Silva Araújo Rezende - 2018.pdf: 3974974 bytes, checksum: d44cb7153672b2c65486e4563be18a44 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2018-04-24T11:52:16Z (GMT) No. of bitstreams: 2 Dissertação - Ana Carolina Da Silva Araújo Rezende - 2018.pdf: 3974974 bytes, checksum: d44cb7153672b2c65486e4563be18a44 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Made available in DSpace on 2018-04-24T11:52:16Z (GMT). No. of bitstreams: 2 Dissertação - Ana Carolina Da Silva Araújo Rezende - 2018.pdf: 3974974 bytes, checksum: d44cb7153672b2c65486e4563be18a44 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2018-03-23 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Titanium is a metal of first choice for use as biomaterial. Titanium alloys of type β are the most suitable for orthopedic implants. This study aims to obtain, characterize structurally and evaluate the bioactivity properties of three types of Ti-Nb-Sn alloys: a) 61% Ti-18% Nb-11% Sn of crude fusion; B) 61% Ti-35% Nb-4% Sn with thermo mechanical treatment; C) 61% Ti-35% Nb-4% Sn with thermomechanical treatment and chemically modified surface. Materials and Methods: samples were obtained by melting in an arc furnace. After melting the Ti-35Nb-4Sn samples were subjected to reduction, treatment and ther malaging. A portion of these Ti-35Nb-4Sn samples had the surface chemically and thermally modified through NaOH, CaCl, heat and water. After this process the three samples were submitted to bioactivity assay through the Kokubo procotol. The samples were immersed in PBS during different periods (1, 3, 7 and 14 days), during this period they were kept in anoven at 36.5 ± 0.03 ° C. It was verified the formation of apatite through XRD and MEV / EDS. The experimental techniques used in the characterization were: MO, DRX, FRX, MEV, and Hardness Test. Results: Structurally the Ti-18Nb-11Sn alloys howed a structure composed of the orthorhombic martensitic phase α ", with Vickers hardness of 189,5HV, MEV images present the formation of Hydroxyapatite in 14 days after immersion in PBS, XRD analysis demonstrates peaks In 2θ = 31,8 ° referring to Hydroxyapatite. The Ti-35Nb-4Sn alloy is formed by β phase, exhibits Vickers hard ness of 270HV, SEM images demonstrating the formation of hydroxyl apatite after 7 days confirmed by XRD. Conclusion: The Ti-18Nb-11Sn alloy, shows composed of orthorhombic martensitic phase, thus presents structural and mechanical characteristics that are not considered appropriate for implants. The bioactivity assay has shown that Ti- 35Nb-4Sn alloys have a more bioactive surface treatment than the others. / O Titânio é um metal de primeira escolha para utilização como biomaterial. As ligas de Titânio do tipo β são as mais indicadas para implantes ortopédicos. Este estudo teve por objetivo obter, caracterizar estruturalmente e avaliar a bioatividade de três tipos de ligas de Ti-Nb-Sn: a) 61%Ti-18%Nb-11%Sn de fusão bruta; b) 61%Ti-35%Nb-4%Sn com tratamento termomecânico; c) 61%Ti-35%Nb-4%Sn com tratamento termomecânico e superfície modificada quimicamente. Materiais e Métodos: as amostras foram produzidas através da fusão em forno arco voltaíco. Após a fusão, às amostras de Ti-35Nb-4Sn foram submetidas à redução, tratamento e envelhecimento térmico. Uma parte destas amostras de Ti-35Nb-4Sn tiveram a superfície modificada quimicamente e termicamente, através de soluções de NaOH, CaCl, Calor e água. Após este processo as três amostras foram submetidas a ensaios de bioatividade, seguindo o procotolo de Kokubo. As amostras foram imersas em um Fluído Corpóreo Simulado (FCS), durante diferentes períodos, (um, três, sete e quatorze dias). Durante este período, foram mantidas dentro da estufa à 36,5 ±0,03°C. Averigou-se a formação de apatita através de DRX e MEV/EDS. As técnicas experimentais utilizadas na caracterização foram: MO, DRX, FRX, MEV, e Ensaio de Dureza. Resultados: estruturalmente a liga Ti-18Nb-11Sn relevou uma estrutura composta pela fase martensítica ortorrômbica α”, com dureza Vickers de 189,5HV, as imagens de MEV apresentam a formação de Hidroxiapatita no 14° dia após a imersão em FCS. A análise de DRX mostra a presença de picos de difração para o ângulo 2θ=31,8°, o qual é referente à formação de Hidroxiapatita. A liga Ti-35Nb-4Sn é apresenta a formação da fase β, a qual apresenta microdureza Vickers de 270HV. As imagens de MEV confirmam a formação de hidroxiapatita após 7 dias de imersão de FCS. Os resultados de DRX também confirmam a presença de hidroxiapatita sobre a superfície da liga. E para as amostras modificadas termoquimicamente, a formação de HA é evidenciada pela MEV, no terceiro dia após imersão em FCS. Conclusão: A liga Ti-18Nb- 11Sn demonstrou ser composta por fase martensítica ortorrômbica, assim, apresenta características estruturais e mecânicas que não são consideradas apropriadas para implantes. O ensaio de bioatividade demonstrou que a liga Ti-35Nb-4Sn com tratamento de termoquímico da superfície, apresenta maior bioatividade que as demais ligas.

Biomateriais para uso em implantes devem exibir propriedades como biocompatibilidade, biofuncionalidade e resistência à corrosão. O uso do titânio e suas ligas em aplicações biomédicas vem continuamente aumentando devido à sua maior taxa resistência-peso, superior biocompatibilidade e resistência à corrosão, boas propriedades mecânicas e baixo módulo de elasticidade quando comparado a outros materiais biomateriais metálicos como aço inox e ligas Co-Cr. Um importante aspecto para o sucesso de um implante é a utilização de materiais com módulo de elasticidade baixo, próximo ao do osso, pois estudos indicam que a transferência insuficiente de carga entre implante e osso pode resultar em reabsorção óssea e afrouxamento do implante, que é chamado efeito de blindagem de tensão (stress shielding effect). A liga ternária Ti13Nb13Zr apresenta em sua composição somente elementos considerados biocompatíveis, possui menor módulo de elasticidade que ligas Co-Cr, aço inox e Ti6Al4V, e superior resistência à corrosão. Neste trabalho foi estudado o efeito do teor de nióbio e zircônio nas propriedades mecânicas da liga ternária TiNbZr numa faixa de composições com quantidade de titânio constante em 74 %peso e teor de Nb e Zr variando entre 6 e 20 %peso, produzida por metalurgia do pó a partir de pós hidrogenados e método de mistura elementar, após diferentes condições de processamento e tratamentos térmicos. Os resultados de caracterização microestrutural obtidos por MEV e difração de raios X mostraram que o aumento do teor de Nb não produziu alterações significativas na fração volumétrica das fases e e, o aumento do teor de Zr proporcionou o aumento da fração de fase , favorecendo a formação da estrutura de Widmanstätten. O aumento dos teores de Nb e Zr produziram alterações nas microestruturas dos materiais que levaram ao aumento dos valores de módulo de elasticidade e dureza, e com aumento do teor de Zr houve aumento da susceptibilidade à corrosão. Nas condições de processamento utilizadas, a liga Ti13Nb13Zr apresentou as propriedades mecânicas e microestruturais mais indicadas para utilização como biomateriais. / Biomaterials for use in implants must be biocompatible, biofunctional and resistant to corrosion. Utilization of titanium and its alloys is continuously increasing due to their larger strength-weight ratio, superior biocompatibility e corrosion resistance, good mechanical properties and low elastic modulus when compared to other metallic biomaterials such as stainless steel and Co-Cr alloys. Using materials with low elastic modulus, close to bone values, is important to reduce stress shielding effect, which can cause implant loosening. Ti13Nb13Zr ternary alloy shows only elements considered biocompatible and has a lower elastic modulus than Co-Cr alloy, stainless steel and Ti6Al4V, and superior corrosion resistance. In this work TiNbZr alloy was prepared in different compositions, maintaining Ti content at 74%wt with Nb and Zr contents ranging amongst 6 and 20%wt, produced by powder metallurgy using different processing conditions and heat treatments. Characterization via SEM and X-Ray diffraction showed that the Nb increase didnt produce significant alterations on volume fraction of and phases in the material, and the increase in Zr content led to an increase in phase amounts and formation of Widmanstätten patterns. Nb and Zr content increasing produced microstructural modifications, leading to an increase in elastic modulus and hardness values, as well as corrosion susceptibility variations, where higher Zr contents leaded to a surface with less corrosion resistance. Amongst compositions and for the designed processing method, Ti13Nb13Zr presented the most indicated mechanical and microstructural properties for utilization as biomaterials.

Thesis (Ph. D. (Physics)) -- University of Limpopo, 2013 / A combination of ball milling experiments and ab initio calculations in this study successfully yielded results that shed light into understanding the fundamental basis for immiscibility and the concept of mechanical alloying in Ti-Mg system. In addition, the conditions for achieving extended solid solubility in elements that usually do not dissolve in each other under thermodynamic equilibrium conditions have been predicted using ultrasoft (US) and norm-conserving (NC) pseudopotentials. Hydostatic pressures required to stabilize ordered phases were determined. Our new systematic representation of martensitic transformation (MT) paths as a result of dislocation necessary to induce α→FCC, α→BCC and α→ω phase transitions led to, for the first time, a direct determination of CRSS and tensile strength for Ti and Mg HCP metals. Furthermore, a new ω phase which is less stable than α phase at 0 GPa is proposed. Based on this phase, α→ω deformation path which yielded the onset of uniaxial transition pressure of 4.167 GPa is reported. Attempts of synthesizing Ti-Mg solid solutions by means of Simoloyer high energy ball mill were not successful; however, nanocrystalline Mg-TiH2-x composites were instead formed. These results were attributed to quick formation of metastable Ti hydrides or cold welding at early stages of BM prior to alloying, thus serving as possible obstacles to forming such solid solutions. The deformed Ti crystals adsorbed H+ from the stearic acid leading to formation of metastable orthorhombic TiH2-x phase which later transformed to a tetragonal TiH2-x or even cubic TiH2 when stoichiometric amount of H2 had been adsorbed. Although the yield was significantly lower, the product of milling a mixture of coarse Mg and fine Ti particles was comprised of Ti particles adhering around ductile Mg particles in a core shell manner. The adhesion of the fine hard titanium particles on the surface of the large ductile magnesium particles impeded the further plastic deformation of the titanium particles, thus suppressing the formation of the faults necessary for mechanical alloying. Nanocrystalline Ti powder of about 40 nm was produced by 30h ball milling. During BM of Ti powder, solid-state transformation from HCP to FCC occurred in the presence of PCA with lattice parameters of 4.242 and 4.240 Å after 24 and 30 h, respectively, v due to protonation. When Ti powder was milled in the absence of PCA, no phase transformation was observed for both uninterrupted and interrupted milling cycles. In addition, nanocrystalline Mg powder with crystallite size varying between 60 and below 40 nm was produced by ball milling. However, no solid-state transformation took place even if the powder was milled for 90 h. Therefore, we evidently report for the first time that the interstitial H+ is the driving force for α → FCC phase transformation in ball milled Ti powder. Our theoretical results predicted the ω phase to be the ground-state structure of Ti at 0K and P=0 GPa, in support of other previously reported calculations. We noticed that the stability of the α phase was surpassed by that of the FCC lattice at ~ 100 GPa, corresponding with sudden sharp rise in c/a ratio, hence attributed to α → FCC phase transition. Similar results were obtained for Mg at 50 GPa, although in this case the crossing of lattice energies coincided with minimum c/a. However, using our proposed HCP→BCC MT path mechanism for Mg, it is evident that the minimum c/a at 50 GPa corresponds to a change in the preferred deformation slip from basal (below 10 GPa) to prismatic rather than phase transition. Nonetheless, the proposed MT model predicts that both elemental Ti and Mg prefer to deform via prismatic slip as indicated by lower shear stress as well as CRSS values compared to those calculated for basal slip. Theoretical findings from ab initio calculations on hypothetical ordered Ti-Mg phases indicated absence of intermetallic phases at equilibrium conditions, in agreement with experimental data. However, the formation becomes possible at 80 GPa and above with respect to c/a ratio but requires at least 200 GPa with respect to stable lattices. Using calculated heats of formation, elasticity and DOS, it has been possible to show that L12 TiMg3 could not form even at high pressure as 250 GPa. Nonetheless, both approaches indicate that forming an intermetallic compound between Ti and Mg requires a crystal structure change, α→FCC for Ti and HCP→BCC for Mg. Proposed DFT-based solid solution model for predicting phase stability and elastic properties of binary random alloys, with Mg-Li system serving as a test case, successfully yielded reliable results comparable to experimental data. This method was successfully applied to study an immiscible Ti-Mg system and the solubility limit vi was for the first time theoretically established. Based on formation energy of Ti-Mg solid solutions, our calculations predicted for the first time that the solubility of up to 60 and 100 at.% Mg into Ti with the use of USP and NCP, respectively, to be thermodynamically favourable with necessary lattice kinetics being the main challenge. Nonetheless, NCP proved to be reliable in predicting structural and elastic properties of disordered alloys.

Le travail consiste en l'optimisation de la microstructure d'un alliage usuel TA6V par obtention de phases métastables. Ces nouvelles microstructures, obtenues par traitements thermiques, permettent d'améliorer la tenue mécanique (statique et en fatigue) de l'alliage sans pour autant changer la biocompatibilité. / This PhD aims at optimizing the microstructure of the usual TA6V alloy by using metastable phases. These new microstructures, obtained by thermal treatments, permit to improve the mechanical strength (static but also the fatigue ones) without modifying the biocompatibility.

β-grain size is an influential microstructural parameter on the properties of titanium components. A reduction of β-grain size is generally associated with improvements to ductility, strength, corrosion and fatigue resistance of many α, α/β and β titanium alloys. During production of wrought titanium components, the β-grain size is carefully controlled during thermomechanical processing but there is currently no control of the β-grain size during solidification of cast components. As such, this inability to control the β-grain structure during solidification may limit the applications for solidification based technologies including casting, welding and direct metal deposition. Due to the limited knowledge of grain refinement practices and the lack of commercial grain refiners for the titanium system, this thesis investigates the mechanisms of β-grain refinement during solidification of cast titanium alloys. In this thesis, generalized theories for grain refinement that have been developed from research into other metallic systems are applied to the titanium system. Similar to the findings from aluminium and magnesium research, it is shown that grain refinement of cast titanium alloys requires the addition of growth restricting solutes which provide constitutional undercooling as well as the presence of potent nucleant particles. It is demonstrated that commercially pure titanium contains a natural distribution of nuclei particles which may originate from the mould wall and when powerful growth restricting solutes are introduced, significant prior-β grain refinement is achievable. All solutes investigated do not interact or poison the naturally occurring nucleants enabling the grain size of the titanium alloys to be predicted by an empirically determined relationship based on the growth restriction factor. A full list of growth restriction factors for various elements in titanium is determined and it is proven that growth restriction theory is valid in the titanium system. A further reduction in β-grain size is achievable by introducing additional nucleant particles to titanium castings in conjunction with growth-restricting solutes. Using a novel technique, titanium powder was introduced to the melt stream prior to solidification and was mixed throughout the liquid. The powder particles partially melted and the oxide surface layer dissolved allowing intimate substrate-liquid contact, enabling the titanium substrates to act as sites for heterogeneous nucleation. Using this technique, it was possible to grain refine commercially pure titanium without foreign elemental addition and when growth restricting solutes were present it was possible to obtain approximately an order of magnitude grain size reduction. The results and concepts developed from this work may aid the future development of a commercial grain refiner for titanium. If a grain refiner is developed, its application will not just be limited to the titanium casting industry but may also benefit other solidification based technologies such as welding, direct metal deposition and wrought billet production.

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

Titanium matrix composites have been extensively evaluated for their potential to replace conventional superalloys in high temperature structural applications, with significant weight-savings while maintaining comparable mechanical properties. The purpose of this investigation is the evaluation of a gamma titanium aluminide alloy with nominal composition Ti-46.5Al-4(Cr,Nb,Ta,B)at.% as a matrix material for use in intermediate temperature applications (400-800㩠in future aerospace transportation systems, as very light-weight structures are needed for cost and weight reduction goals. Mechanical characterization testing was performed over the potential usable temperature range (21-800㩮 Thermal expansion behavior was evaluated, as thermal mismatch of the constituents is an expected problem in composites employing this matrix material. Monotonic testing was conducted on rolled sheet material samples to obtain material properties. The alloy exhibited good strength and stiffness retention at elevated temperatures, as well as improved toughness. Monotonic testing was also conducted on specimens exposed to elevated temperatures to determine the degradation effects of high temperature exposure and oxidation. The exposure did not significantly degrade the alloy properties at elevated temperatures; however, room temperature ductility decreased. Analytical modeling using AGLPLY software was conducted to predict the residual stress state after composite consolidation as well as the potential mechanical behavior of [0]4 laminates with a 㭍ET matrix. Silicon carbide (Ultra-SCS) and alumina (Nextel 610) fibers were selected as potential reinforcing materials for the analysis. High residual stresses were predicted due to the thermal mismatch in the materials. Laminates with Nextel 610 fibers were found to offer the better potential for a composite in this comparison as they provide a better thermal match. Coupons of SCS-6/㭍ET were manufactured with different volume fractions (10% and 20%). Both manufacturing attempts resulted in transverse cracking in the matrix from the residual thermal stress.

The successful use of Nickel-Titanium (Nitinol) in biomedical applications requires an accurate control of its unique mechanical properties. The purpose of this study is to analyze the effects of a wide range of heat treatments on the mechanical behavior of hot-rolled and cold-drawn Nitinol. Results comprise an understanding of the effect of heat treatment temperature and time variation on final material response which is imperative for optimization of material properties. Thirty-three heat treatment variations are tested by combining three durations, 10 minutes, 90 minutes, and 8 hours, with eleven different heat treatment temperatures between 200°C and 440°C. Following heat treatment, the Nitinol samples undergo tensile testing with upper plateau strength, lower plateau strength, ultimate tensile strength, strain to failure, and residual elongation compared for all test groups. Heat treatment "power" is used to describe the efficacy of different combinations of heat treatment temperature and duration. When using hot-rolled Nitinol, results show a low heat treatment power does not create significant precipitation hardening or a significant decrease in martensite transformation stress, resulting in a high upper plateau strength, high residual strain values, and evidence of plastic deformation upon unloading. Moderate power treatments lead to sufficient hardening of the material and a decrease in martensite transformation stress resulting in a pseudoelastic response. Increasing to a high treatment power further decreases the transformation stress and increases the martensite transformation temperature leading to a shape-memory response in hot rolled Nitinol. When using cold-drawn Nitinol, low and moderate heat treatment power levels result in the material exhibiting a pseudoelastic response. Increasing heat treatment power shows the same effects on martensite transformation stress and temperature as seen with the hot-rolled material resulting in a material response transition from pseudoelastic to shape memory.

Thesis (M.S. in M.S.E.)--School of Materials Science and Engineering, Georgia Institute of Technology, 2004. Directed by Roger J. Narayan. / Includes bibliographical references (leaves 87-88).