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1
Kar, Sujoy Kumar. "Modeling of mechanical properties in alpha/beta-titanium alloys." The Ohio State University, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=osu1122570452.
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Barry, Erin Patricia. "Three-dimensional reconstruction of microstructures in [alpha] + [Beta] titanium alloys." Columbus, Ohio : Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1211214635.
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Ward, A. R. "Creep and creep fracture of alpha + beta titanium alloy 6.2.4.6." Thesis, Swansea University, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.639344.
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High precision uniaxial constant stress creep tests were carried out at 773K for the α+β titanium alloy Ti 6.2.4.6. Repeat data at 580 MPa provided a unique opportunity to identify stochastic creep properties and to use this information to build a probabilistic creep damage assessment for this alloy. The stochastic nature of creep properties both at a single test condition (using a generalised gamma distribution) and at various test conditions (by combining this distribution with the Monkman - Grant relation) was identified. In addition, the theta prediction methodology was extended so that life predictions for materials operating under long service conditions can be made that also have a degree of confidence associated with them. Ways in which the theta model can be applied to the fatigue as well as the creep of all materials are also discussed. For comparison purposes two failure criteria are built into the stochastic model and the determinants of failure derived. This stochastic theta model is then used to investigate the nature of the creep failure time distribution for the Ti 6.2.4.6 alloy under constant uniaxial conditions. The corrosion resistance between 723K and 1123K of Ti 6.2.4.6 has also been investigated. There was evidence in favour of parabolic rather than linear increases in weight gain with time and the activation energy associated with parabolic oxidation was estimated at 216KJ/mol. The life of Ti-6246 in argon at 773K was found at certain stresses to be almost twice that obtained in air. This difference could not be explained by the loss of load bearing cross-section area following oxidation. Biaxial creep tests were also carried out at an effective stress of 800 MPa to determine the part taken by the stress state on damage and fracture in the 6.2.4.6 alloy.
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Zheng, Yufeng. "Nucleation Mechanisms of Refined Alpha Microstructure in Beta Titanium Alloys." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1366296464.
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Behera, Amit Kishan. "A Study of Mechanisms to Engineer Fine Scale Alpha Phase Precipitation in Beta Titanium Alloy, Beta 21S." Thesis, University of North Texas, 2013. https://digital.library.unt.edu/ark:/67531/metadc283838/.
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Metastable b-Ti alloys are titanium alloys with sufficient b stabilizer alloying additions such that it's possible to retain single b phase at room temperature. These alloys are of great advantage compared to a/b alloys since they are easily cold rolled, strip produced and can attain excellent mechanical properties upon age hardening. Beta 21S, a relatively new b titanium alloy in addition to these general advantages is known to possess excellent oxidation and corrosion resistance at elevated temperatures. A homogeneous distribution of fine sized a precipitates in the parent b matrix is known to provide good combination of strength, ductility and fracture toughness. The current work focuses on a study of different mechanisms to engineer homogeneously distributed fine sized a precipitates in the b matrix. The precipitation of metastable phases upon low temperature aging and their influence on a precipitation is studied in detail. The precipitation sequence on direct aging above the w solvus temperature is also assessed. The structural and compositional evolution of precipitate phase is determined using multiple characterization tools. The possibility of occurrence of other non-classical precipitation mechanisms that do not require heterogeneous nucleation sites are also analyzed. Lastly, the influence of interstitial element, oxygen on a precipitation during the oxidation of Beta 21S has been determined. The ingress of oxygen and its influence on microstructure have also been correlated to measured mechanical properties.
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Bhattacharyya, Dhriti. "The development of textures and microstructures in alpha/beta titanium alloys." Connect to this title online, 2004. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1086195557.
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Thesis (Ph. D.)--Ohio State University, 2004.Title from first page of PDF file. Document formatted into pages; contains xxii, 220 p. : ill. (some col.). Advisor: Hamish L. Fraser, Materials Science and Engineering. Includes bibliographical references (p. 217-220).
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Goddard, Nicholas David Richard. "Microstructural influence on fatigue in two alpha plus beta titanium alloys." Thesis, Imperial College London, 1988. http://hdl.handle.net/10044/1/47078.
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Searles, Thomas K. "Microstructural characterization of the alpha / beta titanium alloy Ti-6Al-4V." The Ohio State University, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=osu1407510262.
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Sinha, Vikas. "Effects of microstructure on fatigue behavior of [alpha]/[beta] Titanium Alloys /." The Ohio State University, 2000. http://rave.ohiolink.edu/etdc/view?acc_num=osu1488192119263968.
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Kloenne, Zachary Thomas. "Deformation Study of the Novel Alpha/Beta Titanium Alloy, Ti-407." The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1606910373335718.
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Brandes, Matt C. "Creep, Fatigue, And Deformation Of Alpha And Alpha-Beta Titanium Alloys At Ambient Temperature." The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1221848896.
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Lee, Eunha. "Microstructure evolution and microstructure/mechanical properties relationships in [alpha]+[beta] titanium alloys." Connect to this title online, 2004. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1092756139.
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Thesis (Ph. D.)--Ohio State University, 2004.Title from first page of PDF file. Document formatted into pages; contains xxiii, 229 p.; also includes graphics (some col.) Includes bibliographical references (p. 224-229). Available online via OhioLINK's ETD Center
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Bennett, Joe Mancha. "Strengthening of metastable beta titanium alloys." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/284557.
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Using current technology, it is now possible to probe material at atomic length scales, increasing our fundamental understanding of material behavior and properties. Metastable β titanium alloys are a subset of titanium alloys with huge potential for the aerospace sector. However, they exhibit atomic transformations which, even after 60 years of research, are still disputed. For example, these alloys are strengthened using the ω phase, but the mechanism by which this phase forms and its stability are still in question. The aim of this PhD project was to investigate the strengthening of metastable Ti-15wt.%Mo by understanding the stability and transformation pathways which make the metastable β titanium alloy class unique. Athermal ω shares the same composition as the β matrix and is formed by rapid cooling from the β phase field. The classical theory of athermal ω formation is based upon a diffusion-less mechanism in which consecutive pairs of {111}β planes collapse together. However, latest high-resolution electron microscope observations have suggested chemical alterations occur as well, which give reason to challenge this classical formation mechanism. Two novel methods were explored to determine the nature of the ω phase: 1) electron imaging of thin material at different collection angles and 2) total X-ray scattering analysis of large volumes of material. Complementary techniques are invaluable since thin foil artefacts were identified. In particular, a new B2 structured phase in the Ti-15wt.%Mo alloy was observed only in thin electron transparent material. Experimental data from the two new methods were compared to simulations. It was found that a frozen phonon description of the ω structure provided a best fit in both scenarios. The results are therefore consistent with the classical theory of ω formation but the collapse of the {111}β planes towards the ω phase is not considered complete.
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Nag, Soumya. "Influence of Beta Instabilities on the Early Stages of Nucleation and Growth of Alpha in Beta Titanium Alloys." The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1204570232.
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Stevens, Katherine Anne. "The low-cycle fatigue behavior of an alpha-two + Beta Titanium Aluminide Alloy /." The Ohio State University, 2002. http://rave.ohiolink.edu/etdc/view?acc_num=osu1486462702466278.
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Joris, Oliver Pieter Johnathan. "Diffraction experiments on superelastic beta titanium alloys." Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/43967.
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This thesis investigates superelasticity in metastable beta titanium alloys that contain substantial additions of Mo, principally. Superelasticity arises from a reversible transformation from the β to the orthorhombic alpha double prime (α") phase during loading, which was studied principally using in situ synchrotron X-ray diffraction at the I12 beamline at the Diamond synchrotron. Superelastic β-Ti alloys have the potential to be low weight, economical alternatives to NiTi, Gum metal and Ti-2448 for biomedical, military and aerospace applications. The cubic to orthorhombic stress induced martensitic phase transformation is reversible but has an associated permanent deformation. Reducing the permanent deformation associated with cyclic strain is key to the commercial use of these alloys. The effect of β stability on the SE recovery of Ti-Mo, Ti-Mo-Al and Ti-Mo-O alloys has been investigated. Superelastic behaviour was recreated using cyclic strain whilst being examined under in-situ synchrotron X-ray diffraction. Study of the superelastic phase transformation was carried out in-situ due to the reversible nature of the transformation causing the superelastic phase to largely disappear upon unloading. The superelastic behaviour is shown to be sensitive to β stability and in turn composition and temperature. The addition of aluminium and oxygen can be used to enhance both superelastic recovery and strength. The alloys were designed using Morinaga's orbital design approach combined with Laheurte's average valence electron values, tailoring the bond order (Bo) and electronegativity (Md) in order to alter the method of deformation and phase stability. The third alloy design factors considered concern the effect of alloying on the C' modulus of the β, the ω stability and martensite transformation temperatures. Together these methods, whilst semi-empirical, provide a rational basis for alloy design. Both the lowered stiffness and lower apparent stiffness associated with the design method and the transformation respectively could lead to lowering the stiffness of beta Ti alloys towards that of cortical bone. This would reduce the stiffness mismatch that promotes bone re-absorption around surgical implants, reducing the need for implant replacements. Also, the recent developments in eradicating the residual strain associated with the transformation has led to interest from the aerospace industry for possible (high temperature) damping applications. The Ti-Mo binary mechanical curves show a correlation between the apparent yield stress and composition. An increase in Mo concentration from 7.2 at.% was shown to decrease the yield stress to a minimum at 8.2 at.% Mo, after which the yield stress increased. Out of the 5 binary samples, Ti-8.7Mo at.% showed the best superelastic recovery with a recovery of 1.58% strain for a total strain of 2.3%. The yield stress minima is indicative of the composition at which Ms is closest to room temperature. Ti-8.2Mo at.% has the lowest apparent yield stress and Ti-8.7Mo at.% has the largest SE recovery; this correlates well with the theory that the best superelastic behaviour should be observed for an alloy whose composition places it just above As at room temperature. Al additions, which promote the α phase, were found to significantly improve the superelastic behaviour. Al also acts to suppress the ω phase. The ternary alloy Ti-8.1Mo-5Al at.% showed a 95% strain recovery from a total strain of 1.6% at room temperature. Oxygen behaved as a solution strengthener increasing the yield stress and the associated elastic recovery without impeding the austenitic strain recovery transformation. The addition therefore improved both the apparent yield stress and the SE recovery.
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Yannetta, Christopher James. "Additive Manufacturing of Metastable Beta Titanium Alloys." Thesis, University of North Texas, 2017. https://digital.library.unt.edu/ark:/67531/metadc1011883/.
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Additive manufacturing processes of many alloys are known to develop texture during the deposition process due to the rapid reheating and the directionality of the dissipation of heat. Titanium alloys and with respect to this study beta titanium alloys are especially susceptible to these effects. This work examines Ti-20wt%V and Ti-12wt%Mo deposited under normal additive manufacturing process parameters to examine the texture of these beta-stabilized alloys. Both microstructures contained columnar prior beta grains 1-2 mm in length beginning at the substrate with no visible equiaxed grains. This microstructure remained constant in the vanadium system throughout the build. The microstructure of the alloy containing molybdenum changed from a columnar to an equiaxed structure as the build height increased. Eighteen additional samples of the Ti-Mo system were created under different processing parameters to identify what role laser power and travel speed have on the microstructure. There appears to be a correlation in alpha lath size and power density. The two binary alloys were again deposited under the same conditions with the addition of 0.5wt% boron to investigate the effects an insoluble interstitial alloying element would have on the microstructure. The size of the prior beta grains in these two alloys were reduced with the addition of boron by approximately 50 (V) and 100 (Mo) times.
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Chun, Chang Hwan. "Transformation processes and microstructural instability in a beta titanium alloy /." Thesis, Connect to this title online; UW restricted, 1988. http://hdl.handle.net/1773/10578.
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Gupta, Niraj. "First Principles Study of Metastable Beta Titanium Alloys." Thesis, University of North Texas, 2015. https://digital.library.unt.edu/ark:/67531/metadc804949/.
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The high temperature BCC phase (b) of titanium undergoes a martensitic transformation to HCP phase (a) upon cooling, but can be stabilized at room temperature by alloying with BCC transition metals such as Mo. There exists a metastable composition range within which the alloyed b phase separates into a + b upon equilibrium cooling but not when rapidly quenched. Compositional partitioning of the stabilizing element in as-quenched b microstructure creates nanoscale precipitates of a new simple hexagonal w phase, which considerably reduces ductility. These phase transformation reactions have been extensively studied experimentally, yet several significant questions remain: (i) The mechanism by which the alloying element stabilizes the b phase, thwarts its transformation to w, and how these processes vary as a function of the concentration of the stabilizing element is unclear. (ii) What is the atomistic mechanism responsible for the non-Arrhenius, anomalous diffusion widely observed in experiments, and how does it extend to low temperatures? How does the concentration of the stabilizing elements alter this behavior? There are many other w forming alloys that such exhibit anomalous diffusion behavior. (iii) A lack of clarity remains on whether w can transform to a -phase in the crystal bulk or if it occurs only at high-energy regions such as grain boundaries. Furthermore, what is the nature of the a phase embryo? (iv) Although previous computational results discovered a new wa transformation mechanism in pure Ti with activation energy lower than the classical Silcock pathway, it is at odds with the a / b / w orientation relationship seen in experiments. First principles calculations based on density functional theory provide an accurate approach to study such nanoscale behavior with full atomistic resolution, allowing investigation of the complex structural and chemical effects inherent in the alloyed state. In the present work, a model Ti-Mo system is investigated to resolve these fundamental questions. Particular attention is paid to how Mo- (i) influences the bonding in Ti, (ii) distorts the local structure in the Ti lattice, (iii) impacts the point and interfacial defect formation and migration energies, and (iv) affects the mechanism and energetics of b w and wa transformations. Our results are correlated with appropriate experimental results of our collaborators and those in open literature. The modification of Ti bonding by Mo solutes and the attendant distortion of the lattice hold the key to answering the diverse questions listed above. The solutes enhance electron charge density in the <111> directions and, consequently, stiffen the lattice against the displacements necessary for b w transformation. However, Ti atoms uncoordinated by Mo remain relatively mobile, and locally displace towards w lattice positions. This effect was further studied in a metastable Ti-8.3 at.% Mo system with an alternate cell geometry which allows for either b w or $\betaa transformation, and it was found that after minimization Ti atoms possessed either a or w coordination environments. The creation of this microstructure is attributed to both the disruption of uniform b w transformation by the Mo atoms and the overlap of Ti-Mo bond contractions facilitating atomic displacements to the relatively stable a or w structures in Mo-free regions. The vacancy migration behavior in such a microstructure was then explored. Additionally, several minimized configurations were created with planar interfaces between Mo-stabilized b region and its adjacent a- or w- phases, and it was found that the positioning of Mo at the interface strongly dictates the structure of the adjacent Mo depleted region.
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Hill, Davion M. "Microstructure and mechanical properties of titanium alloys reinforced with titanium boride." Columbus, Ohio : Ohio State University, 2006. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1150402807.
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Matychak, Yaroslav, Oleh Yaskiv, Viktor Fedirko, I. Pohreljuk, and Oleh Tkachuk. "Modelling of diffusion saturation of (alpha+beta) titanium alloy by oxygen in rarefied gaseous medium." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-193445.
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Matychak, Yaroslav, Oleh Yaskiv, Viktor Fedirko, I. Pohreljuk, and Oleh Tkachuk. "Modelling of diffusion saturation of (alpha+beta) titanium alloy by oxygen in rarefied gaseous medium." Diffusion fundamentasl 6 (2007) 25, S. 1-2, 2007. https://ul.qucosa.de/id/qucosa%3A13148.
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Dixit, Vikas. "Grain-Boundary Parameters Controlled Allotriomorphic Phase Transformations in Beta-Processed Titanium Alloys." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1357240292.
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Sevilla, Sánchez Pablo. "Functionalization of titanium surfaces with TGF-beta inhibitor peptides." Doctoral thesis, Universitat Politècnica de Catalunya, 2013. http://hdl.handle.net/10803/129568.
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Esta tesis queda enmarcada en el ámbito de los biomateriales metálicos, concretamente en superficies de titanio desarrolladas para la regeneración ósea. Las aplicaciones más habituales del titanio como biomaterial son los implantes dentales y las prótesis de cadera y rodilla. Estos componentes requieren, en servicio, buena estabilidad y fijación al hueso a largo plazo. El titanio es un material idóneo para el cumplimiento de estos requisitos gracias a su alta resistencia mecánica, tenacidad, resistencia a la corrosión y, sobre todo, por su alta capacidad de osteointegración.
En general, el titanio es un biomaterial bioinerte donde, una vez implantado, el tejido vivo genera una fina capa de tejido fibroso alrededor del implante la cual separa el hueso del implante. Un espesor excesivo de esta capa de tejido fibroso puede comprometer la estabilidad e integración del implante y conllevar el fracaso del tratamiento.
El objetivo principal de esta tesis es el desarrollo de una nueva superficie de titanio que sea capaz de controlar e inhibir la generación de tejido fibroso en la superficie del implante. De esta manera, tratamos de mejorar la osteointegración de implantes y prótesis mediante la mejora de la respuesta celular sobre la superficie del implante. Para el control del crecimiento de tejido fibroso en la superficie se han desarrollado nuevas superficies de titanio donde se han inmovilizado dos tipos de péptidos cortos capaces de inhibir la interacción de la citoquina TGF-β, la cual incrementa la producción de este tipo de tejido por parte de las células fibroblásticas. Estos péptidos, llamados P17 y P144 han sido desarrollados por el equipo de nuestro colaborador el Dr. Francisco Borrás-Cuesta, en el Centro de Investigación Médica aplicada de la Universidad de Navarra.
Esta tesis está dividida en 6 capítulos donde se describe el desarrollo y caracterización de las superficies de titanio funcionalizadas con péptidos inhibidores del TGF-β: • Capítulo 1: Introducción a los ámbitos y conceptos importantes de la tesis. • Capítulo 2: Diseño y desarrollo de un método de inmovilización covalente de péptidos cortos sobre superficies de titanio. • Capítulo 3: Estudio de los factores que intervienen en la inmovilización de péptidos cortos sobre las superficies de titanio. • Capítulo 4: Caracterización físico-química de las superficies de titanio funcionalizadas con el péptido P17. • Capítulo 5: Caracterización físico-química de las superficies de titanio
funcionalizadas con el péptido P144. • Capítulo 6: Respuesta biológica in vitro de las superficies de titanio funcionalizadas con P17 y P144.
Los resultados más relevantes en el desarrollo de esta tesis han sido: • El desarrollo de un nuevo método de inmovilización covalente de péptidos sobre superficies de titanio obteniendo una alta densidad de péptido en superficie con una buena estabilidad mecánica y termoquímica. • La consecución de superficies de titanio capaces de inhibir la acción del TGF-β. • Las nuevas superficies desarrolladas son capaces de incrementar la diferenciación osteoblástica y así, potencialmente mejorando la capacidad de osteointegración de implantes y prótesis de titanio.
Este trabajo de investigación contribuye a aumentar el conocimiento sobre la inmovilización covalente y no covalente de péptidos cortos en superficies de titanio. También contribuye en aumentar el conocimiento de la acción e inhibición del TGF-β en células fibroblasticas y osteoblásticas, estas últimas sembradas sobre superficies de titanio. El material desarrollado es un excelente candidato para su aplicación en implantología y traumatología ósea.This thesis is framed in the field of metallic biomaterials, specifically on titanium surfaces developed for bone regeneration. The most common applications of titanium as a biomaterial are dental implants and hip and knee prostheses. These components clinically require good stability and fixation to the bone in the long term. Titanium is an ideal material for these applications as it has high mechanical strength, toughness, corrosion resistance and, above all, a high capacity for osseointegration. In general, titanium is a bioinert material where, once implanted, the living tissue generates a thin layer of fibrous tissue around the implant which separates the bone to the implant. An excessive thickness of this layer of fibrous tissue can compromise the stability and integration of the implant leading to the failure of the biomedical treatment. The main objective of this thesis is the development of a new titanium surface with control and inhibition of the generation of fibrous tissue on the surface of the implant. We aim improving the osseointegration of implants and prostheses by benefiting cellular responses on the surface of the implant. For the control of the formation of fibrous tissue on the surface we have developed new biofunctional titanium surfaces by covalently immobilizing two different short peptides on the metallic substrate. These two peptides are inhibitors of the effect of the cytokine TGF-β1, which increases the production of fibrous tissue by the activity of fibroblastic cells. These peptides, P17 and P144, have been developed by the team of our collaborators at the Dr. Francisco Borrás-Cuesta’s lab, in the Centro de Investigación Médica Aplicada of the Universidad de Navarra This thesis is divided into 6 chapters describing the development and characterization of titanium surfaces functionalized with TGF-β inhibitor peptides: * Chapter 1: Introduction to the areas and important concepts of the thesis. • Chapter 2: Design and development of a method of covalent immobilization of short peptides on titanium surfaces. • Chapter 3: Study of the factors involved in the immobilization of short peptides on the titanium surfaces. • Chapter 4: Physical-chemical characterization of titanium surfaces functionalized with the P17 peptide. • Chapter 5: Physical-chemical characterization of titanium surfaces functionalized with the P144 peptide. • Chapter 6: In vitro biological response of titanium surfaces functionalized with P17 and P144. The most relevant results in the development of this thesis are: • The development of a new method of covalent immobilization of peptides on titanium surfaces with a high density of peptide on the surface and with a good mechanical and thermal-chemical stability. • The development of titanium surfaces with inhibitory action of TGF-β activity. • The developed new surfaces are able to increase osteoblast differentiation, thereby potentially enhancing osseointegration of the biofunctionalized titanium implants and prostheses. This research work contributes to increase the knowledge on covalent and noncovalent immobilization of short peptides on titanium surfaces. It also helps in increasing the knowledge of the action and inhibition of TGF-β on fibroblastic and osteoblastic cells; the later seeded on titanium surfaces. The developed material is an excellent candidate for its application in implantology and orthopedics.
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Jaworski, Allan Wayne. "Effect of microstructure on the room temperature tensile and creep deformation mechanisms of alpha-beta titanium alloys." College Park, Md. : University of Maryland, 2005. http://hdl.handle.net/1903/2388.
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Thesis (Ph. D.) -- University of Maryland, College Park, 2005.Thesis research directed by: Material Science and Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Devaraj, Arun. "Phase Separation and Second Phase Precipitation in Beta Titanium Alloys." Thesis, University of North Texas, 2011. https://digital.library.unt.edu/ark:/67531/metadc67975/.
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The current understanding of the atomic scale phenomenon associated with the influence of beta phase instabilities on the evolution of microstructure in titanium alloys is limited due to their complex nature. Such beta phase instabilities include phase separation and precipitation of nano-scale omega and alpha phases in the beta matrix. The initial part of the present study focuses on omega precipitation within the beta matrix of model binary titanium molybdenum (Ti-Mo) alloys. Direct atomic scale observation of pre-transition omega-like embryos in quenched alloys, using aberration-corrected high resolution scanning transmission electron microscopy and atom probe tomography (APT) was compared and contrasted with the results of first principles computations performed using the Vienna ab initio simulation package (VASP) to present a novel mechanism of these special class of phase transformation. Thereafter the beta phase separation and subsequent alpha phase nucleation in a Ti-Mo-Al ternary alloy was investigated by coupling in-situ high energy synchrotron x-ray diffraction with ex-situ characterization studies performed using aberration corrected transmission electron microscopy and APT to develop a deeper understanding of the mechanism of transformation. Subsequently the formation of the omega phase in the presence of simultaneous development of compositional phase separation within the beta matrix phase of a Ti-10V-6Cu (wt%) alloy during continuous cooling has been investigated using a combination of transmission electron microscopy and atom probe tomography. The results of these investigations provided novel insights into the mechanisms of solid-state transformations in metallic systems by capturing the earliest stages of nucleation at atomic to near atomic spatial and compositional resolution.
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Richardson, Mark D. "Microstructural and mechanical property development in metastable beta titanium alloys." Thesis, University of Sheffield, 2016. http://etheses.whiterose.ac.uk/12663/.
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Titanium alloys represent an ever increasing proportion of the materials employed in aerostructural applications. Metastable beta alloys in particular, offer high specific strength and good corrosion resistance that allow them to compete with steels. Ti-5Al-5Mo-5V-3Cr and Ti-10V-2Fe-3Al are two such alloys used in the main landing gear of large commercial aircraft. Thermomechanical processing of metastable beta alloys is critical in obtaining the desired microstructure, which in turn governs the mechanical properties. This therefore demands a thorough understanding of the relationship between processing, microstructure and mechanical properties in order to optimise the final product and process route. This project characterises the microstructural and mechanical property variation within forged Ti-5553. Microstructural variables are quantified in order to examine their relative influence on mechanical properties. This reaffirmed the importance of microstructural control during materials processing. Gradual changes in primary alpha morphology, beta volume fraction and grain structure were observed throughout the forgings. However, it was also found that the size of secondary alpha precipitates could fluctuate rapidly over relatively short distances. The effect on mechanical properties was significant enough to completely reverse the general trends exhibited over the entire forging. It was also found that the heat treatment response varied with orientation. It would appear that unspecified microstructural variables limited the maximum achievable properties in certain orientations, preventing the heat treatment from further affecting them. However, changes in work hardening behaviour were observed which increased the proof stress while leaving the tensile strength essentially unchanged. The influence of subtransus thermomechanical processing on the microstructural evolution of Ti-10-2-3 was also investigated. Flow curves exhibited an initial peak at low strain followed by extensive flow softening. Microstructural analysis would suggest that the fragmentation and globularisation of acicular alpha particles is at least partially responsible for this softening effect. The use of torsion tests demonstrated that non-linear strain paths may not represent an efficient means of globularising primary alpha. The Burger’s Orientation Relationship (BOR) was found to break down at a linear strain of about 0.5. However, the process of ‘strain reversal’ could partially restore this up to an original linear strain of around 0.8. Solution treatment and ageing revealed that more highly strained regions were less responsive to age hardening.
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Ridland, John. "Synthetic and hydrolytic studies of titanium alkoxides and related complexes." Thesis, University of Newcastle Upon Tyne, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.262881.
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Savage, Michael Francis. "Microstructural and mechanistic study of low temperature creep and dwell fatigue in single colony alpha/beta Titanium Alloys /." The Ohio State University, 2000. http://rave.ohiolink.edu/etdc/view?acc_num=osu1488203857249325.
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Cherukuri, Balakrishna. "Microstructural Stability and Thermomechanical Processing of Boron Modified Beta Titanium Alloys." Wright State University / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=wright1229656783.
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Hastings, Philip John. "The behaviour of short fatigue cracks in a beta-processed titanium alloy." Thesis, University of Nottingham, 1989. http://eprints.nottingham.ac.uk/28458/.
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An investigation has been made into the behaviour of short fatigue cracks in the β-processed titanium alloy, Ti6Ss. The effect on the material of a number of different variables was studied, particularly microstructure, as well as stress level, specimen design and specimen size. Initiation of cracks was found to occur at similar microstructural features in smooth specimens, regardless of a-platelet morphology. Cracks initiated from slip bands across small bundles of α-platelets, despite the presence of longer, more intense slip bands across α-colonies. α-platelet morphology was found to have a significant effect on short crack propagation rates when crack length was of the order of, or less than, the α-colony size - the more aligned the α-platelets, the greater the short crack propagation rates at equivalent ΔKs. Increasing the prior β-grain size (and hence the a-colony size) led to higher short crack propagation rates at equivalent ΔKs. Specimen design appeared to have an effect on short crack growth rates a uniaxial tension specimen design gave slightly higher growth rates than a four point bend specimen design. Variation in specimen size had no effect on short crack growth rates for the same microstructural condition, but a larger specimen size was found to reduce the scatter in specimen lives observed in smaller specimens. Short crack growth rates were apparently insensitive to stress level when compared at the same nominal ΔK values. Crack shape was found to vary considerably at crack depths below approximately 0.75mm. At crack depths greater than this value, cracks took an approximately semi-circular form. In keeping with many recent studies of short crack behaviour, short cracks were found to grow faster than long cracks at the same nominal ΔKs and at ΔKs below the long crack threshold value, ΔKth· A case study was carried out to determine the behaviour of short cracks in a cheese forged from an ingot slice of IMI685. Crack growth behaviour was found to be the same as that of Ti65s, but initiation behaviour was affected by the presence of pores in the IMI68S, leading to a significant reduction in fatigue life.
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Mbafor, William Fru. "Synthesis, characterisation and application of zeolite titanium (Al) beta in organic transformations." Thesis, University of Liverpool, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.367145.
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Koduri, Santhosh K. "Application of Bayesian Neural Network Modeling to Characterize the Interrelationship between Microstructure and Mechanical Property in Alpha+Beta-Titanium Alloys." The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1275402649.
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Shariff, Tasneem. "Laser welding of a near-beta titanium alloy Ti-5 Al-5Mo-3Cr." Thesis, McGill University, 2011. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=96874.
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Titanium alloys are widely used in the aerospace industry due to their high specific strength and excellent corrosion resistance. However, for some large scale aircrafts, such as Airbus A380 and Boeing 787, there is a demand for even stronger Ti alloys for structural and load bearing applications. Ti-5Al-5V-5Mo-3Cr (Ti-5553) is a new metastable β titanium alloy that exhibits excellent strength characteristics, even higher than the currently used α-β titanium grades, such as the workhorse Ti-6Al-4V alloy. It is expected that Ti-5553 will gain wider applications in the future and hence its weldability needs to be addressed. The current work is aimed at investigating the laser weldability of Ti-5553. Autogenous welds were produced by varying the defocusing distance and weld speed. The weld quality was investigated in terms of the surface morphology, welding defects, microstructure, hardness, and tensile properties. It was determined that welds with full penetration could be achieved and defects could be maintaned to meet aerospace specification tolerances by carefully manipulating the defocusing distance and weld speed within an optimum processing window. Welding was also conducted with Ti-6Al-4V filler wire and the effect of varying joint gaps was investigated on the metallurgical and tensile properies of Ti-5553 laser welds. It was found that welds with full penetration could be produced upto a gap of 0.5 mm for 3.1 mm thick plates. Increasing the joint gap, and hence the amount of filler wire resulted in the presence of martensite which was due to the incomplete and nonuniform mixing of base material and filler wire.Les alliages de titan sont beaucoup utilises dans l'industrie aérospatiale à cause de leurs caractéristiques de haute dureté et de la résistance à la corrosion. Néanmoins, pour les avions de grande taille, tels que Airbus A380 et Boeing 787, une dureté plus haute est requise dans les applications de support structurel. Ti-5Al-5V-5Mo-3Cr (Ti-5553) est une nouvelle alliage de titan fait de β métastable qui démontre les caractéristiques de dureté qui sont supérieurs à d'autres alliages de α-β de titan qui sont utilisées présentement, en incluant l'alliage de Ti-6Al-4V. Il est attendu que l'utilisation de l'alliage de Ti-5553 se répandra dans l'avenir, pour cela, la question de soudage de ce matériel doit être adressée. Le travail actuel recherche l'habilité de soudage à laser de Ti-5553. Les autogènes soudures ont étés produites en changeant la distance du centre d'intérêt et en variant la vitesse de soudage. La qualité des soudures a été analysée selon l'anatomie de la surface, des défauts de soudage, de la microstructure, de la dureté et des propriétés de traction. Il a été détermine qu'on peut obtenir les soudures de pleine pénétration et qu'on peut atteindre les spécifications aérospatiales de tolérance des défauts en contrôlant soigneusement la distance du centre d'intérêt ainsi que la vitesse de soudage dans une fenêtre de processus optimisée. Le soudage a aussi été conduit avec fil languette de Ti-6Al-4V et l'effet de variation de l'espace entre les jonctions sures les propriétés de traction et sure métallurgie de soudures de Ti-5553 a été investiguée. Il a été constaté qu'on peut obtenir les soudures de pleine pénétration jusqu'une espèce entre les jonctions de 0.5 mm pour les plaques d'épaisseur de 3.1mm. La présence de martensite a été constatée pour une distance entre les jonctions plus grand ayant plus de quantité de fil languette. Martensite s'est formée à cause d'un mélange non uniforme et incomplet entre le matériel de base et celui du fil languette.
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Peterson, Benjamin Howard. "A Combinatorial Approach to the Development of a Creep Resistant Beta Titanium Alloy." The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1218488816.
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Broderick, Thomas Froats. "The Influence of Microstructure on the Deformation Behavior of Beta Solution Heat Treated and Aged Ti-6Al-2Sn-2Zr-2Mo-2Cr-0.18Si." The Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=osu1263951781.
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Tungala, Vedavyas. "Exceptional Properties in Friction Stir Processed Beta Titanium Alloys and an Ultra High Strength Steel." Thesis, University of North Texas, 2017. https://digital.library.unt.edu/ark:/67531/metadc984167/.
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The penchant towards development of high performance materials for light weighting engineering systems through various thermomechanical processing routes has been soaring vigorously. Friction stir processing (FSP) - a relatively new thermomechanical processing route had shown an excellent promise towards microstructural modification in many Al and Mg alloy systems. Nevertheless, the expansion of this process to high temperature materials like titanium alloys and steels is restricted by the limited availability of tool materials. Despite it challenges, the current thesis sets a tone for the usage of FSP to tailor the mechanical properties in titanium alloys and steels. FSP was carried out on three near beta titanium alloys, namely Ti6246, Ti185 and Tiβc with increasing β stability index, using various tool rotation rates and at a constant tool traverse speed. Microstructure and mechanical property relationship was studied using experimental techniques such as SEM, TEM, mini tensile testing and synchrotron x-ray diffraction. Two step aging on Ti6246 had resulted in an UTS of 2.2GPa and a specific strength around 500 MPa m3/mg, which is about 40% greater than any commercially available metallic material. Similarly, FSP on an ultra-high strength steel―Eglin steel had resulted in a strength greater than 2GPa with a ductility close to 10% at around 4mm from the top surface of stir zone (SZ). Experimental techniques such as microhardness, mini-tensile testing and SEM were used to correlate the microstructure and properties observed inside SZ and HAZ's of the processed region. A 3D temperature modeling was used to predict the peak temperature and cooling rates during FSP. The exceptional strength ductility combinations inside the SZ is believed to be because of mixed microstructure comprised of various volume fractions of phases such as martensite, bainite and retained austenite.
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Herbig, Michael. "3D short fatigue crack investigation in beta titanium alloys using phase and diffraction contrast tomography." Phd thesis, INSA de Lyon, 2011. http://tel.archives-ouvertes.fr/tel-00690521.
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X-Ray Diffraction Contrast Tomography (DCT) is a recently developed, non-destructive synchrotron imaging technique which characterizes microstructure and grain orientation in polycrystalline materials in three dimensions (3D). By combining it with propagation based phase contrast tomography (PCT) it is for the first lime possible to observe in situ the 3D propagation behavior of short fatigue cracks (SFCs) within a set of fully characterized grains (orientation and shape). The combined approach, termed 3D X-ray Tomography of short cracks and Microstructure (3DXTSM), has been developed on the metastable beta titanium alloy "Beta21S". A large part of this work deals with the development of the 3DXTSM methodology. In the combined dataset, each point on the 3D fracture surface can be associated with a multidimensional data structure containing variables describing the grain orientation, the local fracture surface normal and the propagation history. The method uses a surface mesh composed of triangles that describes the crack (in other words: the fracture surface) in the last propagation state measured. Grain orientations, crack fronts, local growth rates and grain boundaries can be visualized by assigning colors to this mesh. The data structure can be interrogated in a number of different ways. Tools for extracting pole figures and pole density distribution functions have been implemented. An algorithm was developed that is capable of measuring the 3D local growth rate of a crack containing branches. The accuracy of the grain boundaries as reconstructed with OCT was evaluated and the elastic constants of Beta21S were determined.
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Hudson, Candi Monica. "Investigation of low temperature creep deformation behavior of a metastable beta Titanium-14.8Wt%Vanadium alloy." College Park, Md. : University of Maryland, 2004. http://hdl.handle.net/1903/1729.
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Thesis (Ph. D.) -- University of Maryland, College Park, 2004.Thesis research directed by: Material Science and Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Epshteyn, Albert. "Synthesis, stability, and reactivity of high-oxidation-state pentamethylcyclopentadienyl acetamidinate [beta]-Hydride- or [beta]-Methide-bearing alkyl complexes of zirconium, titanium, and tantalum." College Park, Md. : University of Maryland, 2006. http://hdl.handle.net/1903/4249.
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Thesis (Ph. D.)--University of Maryland, College Park, 2006.Thesis research directed by: Chemistry. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Sanguinetti, Ferreira Ricardo Artur. "Influence des séquences de traitements thermiques sur les transformations structurales de l'alliage beta-cez : aspects cinétiques et morphologiques." Vandoeuvre-les-Nancy, INPL, 1994. http://www.theses.fr/1994INPL093N.
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Les séquences de transformations de phases des alliages de titane beta-cez et ti-6246 ont été étudiées au cours de différentes séquences thermiques. Plusieurs techniques ont été utilisées pour mettre en évidence les changements structuraux. Les différentes transformations se produisant au cours du chauffage et de la mise en solution dans le domaine (alpha+beta) ont été étudiées pour les trois structures initiales différentes. Nous avons montré qu'un mélange (beta métastable + oméga trempé) se décompose différemment suivant la vitesse de chauffage. Pour les vitesses les plus lentes la phase beta transitoire se décompose d'abord en phase oméga et puis en phase alpha amas qui coalescent pour former des lamelles à plus hautes températures. Au voisinage de 700c, un maximum de taux de phase alpha est observé quelle que soit la vitesse du chauffage. Au-delà de cette température, seule l'homogénéisation de la matrice, la dissolution partielle et la coalescence de la phase alpha sont observées, mécanismes qui se poursuivent au cours du maintien. Pour une structure (beta transitoire + alpha + alpha amas) issue d'un refroidissement lent, seule une faible croissance de la phase alpha se dissout complètement. Au-delà de 700c et au cours du maintien les changements structuraux sont identiques à ceux observés pour la structure précédente. Pour ces deux structures initiales, la morphologie d'alpha, après mise en solution en alpha + beta est très différentePhase transformation sequances of the beta-Cez and Ti-6246 titanium alloys were studied during several thermal treatments. Several technics were used to show the structural changes : transmission electron microscopy, X-ray diffraction patterns, electrical resistance and analytical electron microscopy. The different transformation sequences occurring during heating and (alpha+beta) annealing treatments were studied for three initial structures for the beat-Cez alloy, which present different degree of metastability obtained by different cooling rates from the stable beta temperature range. We showed that an initial structure (beta metastalbe + omega anisothermal) transforms in different ways depending on the heating rate. For a slow heating rate, the omega phase precipites in the beta transient matrix followed by alpha clusters ; which coarsen to form the alpha lamellae at higher temperatures; For a rapid heating rate (Vc=5 degrés C/s), the omega phase is not observed. However, a supposed orthorhombixal phase is observed nearby 450 C. Whatever the reating rate, a maximum of alpha phase content is observed up to 700 C. For temperatures higher than 700 C, the matrix homogenization and the dissolution and coarsening of alpha phase are observed, up to 830 C and continue during the annealing treatments. For an initial structures (beta metastable + alpha + alpha clusters) stemed from the beta range during a slow cooling (1,5 C/s), only a weak growth in the alpha phase is observed during heating up to 560 C. After this temperature, alpha clusters dissolve themselves up to 700 C. For temperature higher than 700 C, the same structural changes as for the previous initial microstructure are observed
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Ramsteiner, Ingo Benedict. "High energy x-ray study of short range order and phase transformations in titanium-vanadium." [S.l. : s.n.], 2005. http://www.bsz-bw.de/cgi-bin/xvms.cgi?SWB12168122.
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Golozar, Mehdi. "Plasma electrolytic oxide coatings on low-modulus [beta]-type titanium alloys : applications to load-bearing orthopaedic implants." Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.709079.
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Muradás, Rodrigo Ricabone. "Mecano-síntese e caracterização de ligas de Ti-Nb-Sn." UNIVERSIDADE ESTADUAL DE PONTA GROSSA, 2006. http://tede2.uepg.br/jspui/handle/prefix/1409.
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Previous issue date: 2006-10-31Mechanical alloying is a powder processing technique involving cold welding, fracturing mechanisms and rewelding of powder particles in a ball mill. The present work applied this technique with the purpose of processing titanium, niobium and tin alloys, through planetary ball mill and attritor mill. The atomic percentages of these elements were varied in six differents ways. The niobium hydrate was used on production of some alloys in study, with the purpose to observe the effects during the milling and on the alloys obtained after sintering. Differences between processing in planetary ball mill and attritor mill, as well the cold welding influences on the kinetic parameters of milling process were approached. The use of niobium hydrate result in a decrease of powders average crystallite size, and an increase of micro hardness of sintered alloys. This work obtained beta titanium alloys and alpha-beta titanium alloys in namometric sizes. The average crystallite size, for milled powders, was 7,6 nm.
Mecano-síntese é uma técnica de processamento em pó que envolve a soldagem a frio, mecanismos de fratura e a resoldagem das partículas de pós, em moinhos de bolas. O presente trabalho utilizou esta técnica com o propósito de processar ligas de titânio, nióbio e estanho, através de moinhos de bolas planetário e de atrito. As porcentagens atômicas destes elementos foram variadas de seis maneiras diferentes. O hidreto de nióbio foi utilizado na produção de algumas ligas em estudo, com o propósito de se observar os efeitos durante a moagem e na liga obtida após a sinterização. Diferenças entre o processamento em moinho de bolas planetário e o moinho de atrito, assim como as influências da soldagem a frio nos parâmetros cinéticos do processo de moagem, foram abordadas. O uso do hidreto de nióbio resultou na diminuição do tamanho médio de cristalito dos pós, e em um acréscimo na microdureza das ligas sinterizadas. Neste trabalho foram obtidas ligas de titânio beta e de titânio alfa-beta, em tamanhos nanométricos. O tamanho médio do cristalito, para os pós moídos, foi de 7,6 nm.
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Aleixo, Giorgia Taiacol. "Estabilidade e metaestabilidade de fases em ligas Ti-Nb." [s.n.], 2006. http://repositorio.unicamp.br/jspui/handle/REPOSIP/263173.
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Orientadores: Rubens Caram Junior, Conrado Ramos Moreira AfonsoDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica
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Resumo: Ligas de titânio formam a classe mais versátil de materiais metálicos utilizados para aplicações biomédicas. As ligas de Ti tipo ß usadas em dispositivos ortopédicos envolve, além de excelentes propriedades como baixa densidade, elevada resistência mecânica e excepcional resistência à corrosão, a biocompatibilidade com elementos de liga, tais como Nb, Ta, Zr e Mo. O objetivo deste trabalho foi analisar a estabilidade e metaestabilidade de fases em ligas tipo ß no sistema Ti-Nb através da verificação da influência do teor de nióbio sob diversas condições de tratamento térmico. Para tanto variou-se a adição de Nb de 5% a 30% em peso na liga, obtendo amostras que foram submetidas a condições distintas de resfriamento a partir do campo ß. Amostras obtidas foram caracterizadas no tocante à microestrutura via microscopia ótica, eletrônica de varredura e de transmissão, difração de raios-X, enquanto o comportamento mecânico foi preliminarmente avaliado através de ensaios de dureza Vickers e de medidas de módulo de elasticidade através de técnicas acústicas. Os resultados obtidos indicam que baixas taxas de resfriamento conduzem à microestrutura de equilíbrio (a+ß) enquanto que altas taxas de resfriamento levaram à formação de estruturas metaestáveis. À medida que o teor de Nb foi incrementado e sob altas taxas de resfriamento, obteve-se, respectivamente, martensita a¿ (hexagonal compacta), martensita a¿ (ortorrômbica), fase ? (trigonal) e finalmente, fase ß metaestável. Em relação ao módulo de elasticidade, observou-se que esse parâmetro decresce entre 0 e 15% de Nb e após este último valor, tal constante elástica se eleva como resultado da precipitação de fase ? bem como da possível alteração de dimensões da estrutura cristalina. As ligas Ti-Nb apresentaram uma variabilidade de microestruturas e propriedades que dependem fortemente da composição e condição de resfriamento
Abstract: Titanium alloys form one of the most versatile classes of metallic materials used for biomedical applications. ß Ti alloys for orthopaedic devices involves, besides excellent properties like low density, high mechanical strength and good corrosion resistance, great biocompatibility with alloying elements, such as Nb, Ta, Zr and Mo. The objective of this work was to analyze the stability and metastability of phases in ß Ti-Nb alloys through the evaluation of the influence of percentage of Nb obtained in different heat treatment conditions. In this way, Nb addition was varied from 5 to 30wt% in Ti-Nb system. Samples were obtained and microstructural characterization was made through optical microscopy, scanning and transmission electron microscopy and X-ray diffraction, while mechanical behavior was primarily evaluated by Vickers hardness and elasticity modulus through acoustic techniques. The results obtained indicate that lower cooling rates resulted in the equilibrium microstructures (a+ß), otherwise higher cooling rates led to formation of metastable structures. As the Nb content was increased and under greater cooling rates, it was obtained, respectively, martensite a¿ (hexagonal closed packed), martensite a¿ (orthorhombic), ? phase (trigonal) and finally, metastable ß phase. Regarding modulus of elasticity it was observed that it decreases as the %Nb increases up to 15% and beyond this percentage the modulus increases due the precipitation of ? phase as well as possible variation of crystalline structure dimensions. Ti-Nb alloys presented a great variety of combinations between microstructures and properties that strongly depends on composition and cooling conditions
Mestrado
Materiais e Processos de Fabricação
Mestre em Engenharia Mecânica
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Mavros, Nicholas C. "Advanced Manufacturing of Titanium Alloys for Biomedical Applications." Cleveland State University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=csu1527771497260907.
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Ndali, Busongo Faustine [Verfasser]. "Influence of Heat Treatment on the Microstructure and Mechanical Properties of the Titanium Alloy Beta 21S / Faustine Ndali Busongo." Aachen : Shaker, 2005. http://d-nb.info/1186588438/34.
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Burton, Robert M. "Oxidant concentration effects in the hydroxylation of phenol over titanium-based zeolites Al-free Ti-Beta and TS-1." Thesis, Stellenbosch : University of Stellenbosch, 2006. http://hdl.handle.net/10019.1/2366.
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Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2006.This work focuses on the effects of hydrogen peroxide concentration on the catalytic activity and product selectivity in the liquid-phase hydroxylation of phenol over titanium-substituted zeolites Al-free Ti-Beta and TS-1 in water and methanol solvents. Hydroquinone is typically the desired product, and these solvents employed have previously been shown to be of importance in controlling the selectivity of this reaction. Different volumetric quantities of an aqueous 30 wt-% peroxide solution were added to either water or methanol solutions containing the catalyst and phenol substrate, and the reaction monitored by withdrawing samples over a period of 6-8 hours. For Al-free Ti-Beta catalysed reactions, the peroxide concentration affects the selectivity and activity differently in water and methanol solvents. Using methanol solvent, the selectivity to hydroquinone formation is dominant for all peroxide concentrations (p/o-ratio > 1), and favoured by higher initial peroxide concentrations (> 1.27 vol-%), where p/o-ratios of up to can be reached; in water solvent, increasing the peroxide concentration above this level results in almost unchanging selectivity (p/o-ratio of ca. 0.35). For lower peroxide concentrations in water, the p/o-ratio increases slightly, but never exceeds the statistical distribution of ca. 0.5. Using water as a solvent, higher phenol conversion is obtained as the initial peroxide concentration increases; in methanol the phenol conversion is largely independent of peroxide concentration. As expected for the smaller pore TS-1, higher hydroquinone selectivity is obtained in methanol than for Al-free Ti-Beta, which is consistent with shape-selectivity effects enhanced by the use of this protic solvent. Interestingly, with TS-1 the p/o-ratio is higher at lower phenol conversions, and specifically when the initial peroxide concentration is low (p/o-ratio exceeding 3 were obtained at low phenol conversion), and decreases to a near constant value at higher conversions regardless of the starting peroxide concentration. Thus, low peroxide concentrations favour hydroquinone formation when TS-1 is used as the catalyst. Comparing the performance of the two catalysts using methanol solvent, the phenol conversion on TS-1 is more significantly influenced by higher hydrogen peroxide concentrations than Al-free Ti-Beta. However, with higher initial concentrations the unselective phenol conversion to tars is more severe since the hydroquinone selectivity is not higher at these high peroxide concentrations. The increased tar formation, expressed as tar deposition on the catalyst or as the tar formation rate constant, confirms that the greater amount of free-peroxide present is mainly responsible for the non-selective conversion of phenol. Kinetic modelling of the reaction data with an overall second-order kinetic model gave a good fit in both solvents, and the phenol rate constant is independent of changing hydrogen peroxide concentration for the hydroxylation over Al-free Ti-Beta using water as the solvent (kPhenol = 1.93 x 10-9 dm3/mmol.m2.s). This constant value suggests that the model developed to represent the experimental data is accurate. For TS-1 in methanol solvent the rate constant is also independent of peroxide concentration (kPhenol = 1.36 x 10-8 dm3/mmol.m2.s). The effect of the method of peroxide addition was also investigated by adding discrete amounts over a period of 4.5 hours, and was seen to improve hydroquinone selectivity for reaction on both catalysts, and most significantly for Al-free Ti-Beta in methanol solvent. With TS-1, the mode of peroxide addition had little influence on phenol conversion, but the initial selectivity to hydroquinone was ca. 1.6 times higher than for an equivalent single-portion addition (at a similar phenol conversion). Discrete peroxide addition for hydroxylation in methanol over Al-free Ti-Beta gave greatly improved hydroquinone selectivities compared to the equivalent single-dose addition. Compared to TS-1, the initial selectivity was not as high (p/o-ratios of 0.86 and 1.40 respectively at 10 mol-% phenol conversion), but this can be explained on the basis of geometric limitations in the micropores of TS-1 favouring hydroquinone formation. The final selectivity, however, is marginally higher (using the same mode of peroxide addition, and at the same phenol conversion). Discrete peroxide addition has an additional benefit in that it also reduces the quantity of free-peroxide available for product over-oxidation, and consequently reduces the amount of tars formed. Thus, the interaction of the effects of peroxide concentration and the solvent composition and polarity on the product selectivity and degree of tar formation is important. Particularly with TS-1, lower peroxide concentrations in bulk methanol solvent are highly beneficial for hydroquinone formation, because of the implicit geometric constraints in the micropores, the lower water concentration, and the decreased tar formation associated with high methanol concentrations. This could have significant reactor design implications, as the results obtained here suggest that the reaction should be terminated after approximately 30 minutes to maximise hydroquinone production (under the conditions evaluated in these experiments), even though the corresponding phenol conversions are low (ca. 10 mol-%). The higher hydroquinone selectivities reached at low phenol conversions for the discrete peroxide addition experiments also confirm this. Practically, to enhance the hydroquinone selectivity for reaction over TS-1, the initial phenol-peroxide molar ratio should be ca. 10, methanol should constitute not less than 90 vol-% of the reaction volume, and the peroxide should be added in discrete amounts. For reaction over Al-free Ti-Beta, methanol solvent also enhances the hydroquinone formation as expected. At low phenol conversions (ca. 10 mol-%) hydroquinone is still the preferred product, although in contrast to TS-1 the selectivity increases with phenol conversion, and is higher with higher initial peroxide concentrations. Under the best conditions evaluated here for optimal hydroquinone formation, the initial phenol-peroxide molar ratio should be ca. 2.5, with methanol making up at least 90 vol-% of the total volume. Discrete peroxide addition in methanol solvent for the Al-free Ti-Beta catalysed hydroxylation gives excellent improvements in hydroquinone selectivity (2.5 times higher than water solvent), and the addition in more discrete portions might further improve hydroquinone formation, and should therefore be examined.
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Busongo, Faustine Ndali [Verfasser]. "Influence of Heat Treatment on the Microstructure and Mechanical Properties of the Titanium Alloy Beta 21S / Faustine Ndali Busongo." Aachen : Shaker, 2005. http://nbn-resolving.de/urn:nbn:de:101:1-2019051908540573121440.
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Hendrickson, Mandana. "The Role of Misfit Strain and Oxygen Content on Formation and Evolution of Omega Precipitate in Metastable Beta-titanium Alloys." Thesis, University of North Texas, 2016. https://digital.library.unt.edu/ark:/67531/metadc955080/.
Full textAbstract:
β-Ti alloys are widely used in airframe and biomedical applications due to their high ductility, high hardenability, and low elastic modulus. The phase transformations in β-Ti alloys are rather complex due to formation of metastable phases during various thermo-mechanical treatments. One such critical metastable phase, the hexagonal omega (ω) phase, can form in β-Ti alloys under quenching from the high temperature β phase and/or isothermal aging at intermediate temperature. Despite a substantial amount of reported works on the ω phase, there are several critical issues related to the ω formation need to be resolved, e.g. role of alloying elements and oxygen content. Therefore, this dissertation has attempted to provide insights into ω transformation in low misfit (Ti-Mo) and high misfit (Ti-V) binary systems as well as multicomponent (Ti-Nb-Zr-Ta) alloys.
The evolution of ω structure, morphology and composition from the early stage (β-solution+quenched) to later stages after prolonged aging are systematically investigated by coupling transmission electron microscopy (TEM), atom probe tomography (APT) and high-energy synchrotron X-ray diffraction techniques. The influence of aging temperature and duration on characteristic of ω phase in Ti-Mo, and Ti-V alloys is addressed in details. It is found that compositional changes during aging can alter the structure, size and morphology of ω precipitates. In low misfit alloys, the ellipsoidal morphology of ω phase was retained during isothermal aging, while in high misfit alloys it changed from ellipsoidal to cuboidal morphology after prolonged aging. Secondly, ω transformation in biomedical Ti-Nb-Zr-Ta alloy is probed in which the micro-hardness was sensitive to microstructural changes. Furthermore, the evolution of oxygen concentration in ω precipitates during various aging conditions in binary Ti-Mo and Ti-V alloys are reported. It has been accepted that interstitial elements such as oxygen can largely alter mechanical behavior and the microstructure of Ti-alloys. Recently, oxygen is intentionally added to some biomedical alloys to improve their performances. However, a careful understanding of the effect of oxygen on ω phase transformation is still lacking in the literature. In this work, the role of oxygen on ω phase formation in biomedical TNTZ alloys is investigated. Although it is traditionally accepted that oxygen suppresses ω transformation, our observations revealed contradictory results during isothermal aging of TNZT alloys. The results of our investigations provide a novel insight into understanding the effect of interstitial elements on metastable phase transformation in β-Ti alloys. It is concluded that depending upon the nature of alloying elements and/or the applied thermo-mechanical treatments, oxygen may play a different role in ω transformations.