As ligas Ti-??constituem um grupo promissor de ligas de titânio em termos de processamento, propriedades e aplicações potenciais. Além do projeto da liga em termos de composição, a obtenção de microestruturas adequadas por meio de tratamentos térmicos é necessária para otimizar o balanço entre resistência mecânica e tenacidade. O presente trabalho teve por objetivo estudar o comportamento em fadiga de alto ciclo da liga Ti-13V-11Cr-3Al, uma liga de alta resistência mecânica destinada ao emprego na indústria aeroespacial, sob duas condições de tratamento. O material foi recebido na forma de barras com 7,6 mm de diâmetro, apresentando microestrutura composta por grãos alongados e propriedades em tração combinando alto limite de resistência (1.479 MPa) e razoável ductilidade (deformação verdadeira de fratura igual a 0,217). O material foi tratado termicamente em duas condições: recozimento a vácuo a 750?C por 1 h com resfriamento lento, e tratamento flash em banho de sal a 650?C por 6 min, com posterior têmpera em água. O tratamento flash resultou em melhor combinação de resistência mecânica e ductilidade, avaliadas pelo ensaio de tração. O estudo da resistência à fadiga baseou-se na obtenção de curvas ?/N por meio de ensaios de flexão rotativa (R = -1) empregando-se corpos de prova do tipo viga em balanço. Para cada condição microestrutural, foram obtidas duas curvas ?/N, uma com amostras polidas e outra empregando-se corpos de prova com concentradores de tensão geométricos (entalhes), visando avaliar a sensibilidade ao entalhe desta liga nas duas condições microestruturais. O material submetido ao tratamento flash apresentou maior dispersão e menor resistência à fadiga, comparado ao material recozido; no entanto apresentou também menor sensibilidade ao entalhe em vidas longas (106 ciclos). O trabalho foi complementado por exames fractográficos para a identificação dos pontos de iniciação da fratura. / The Ti-??alloys are a promising group of titanium alloys in terms of processing, properties and potential applications. In order to achieve the optimum balance between strength and toughness it is necessary, besides determining a proper composition in the alloy design, to obtain suitable microstructures by means of thermo-mechanical process and heat treatment. This study aimed to assess the high cycle fatigue behavior of Ti-13V-11Cr- 3Al alloy, a high-strength alloy intended for use in the aerospace industry. The material was received in the form of bars with 7.6 mm in diameter, whose microstructure comprises elongated grains and whose mechanical properties combines high tensile strength (1,479 MPa), and reasonable ductility (true strain fracture equal to 0.217). The material was heat treated in two conditions: vacuum annealing at 750?C for 1 h with slow cooling, and flash 650?C salt bath for 6 min with subsequent water quenching. The study was based on obtaining ??/ N curves through by rotary bending (R = -1) fatigue tests employing cantilever beam specimens. For each microstructural condition, two ??/ N curves were obtained, the former with smooth samples and the latter employing specimens with geometric stress concentrators (notches), to evaluate the notch sensitivity of this alloy in both microstructural conditions. The material subjected to flash treatment showed greater dispersion and lower fatigue strength compared to annealed; however also showed lower notch sensitivity at long life (106 cycles). The study was complemented by fractographics analysis to identify the fracture initiation points.

Titanium and its alloys constitute an important class of materials for aerospace, biomedical, and chemical industries, primarily due to their high specific strength and fracture toughness with good corrosion resistance. Owing to their hexagonal crystal structure at room temperature, both microstructure and texture play a crucial role in the processing and hence the properties of titanium alloys. The basis for tailoring the microstructure and texture in titanium alloys centers around the transformation of high temperature β (body-centered cubic) to the low temperature α (hexagonal close packed) phase. One of the most widely used titanium alloy is Ti-6Al-4V, which exists as two phase (α+β) alloy at room temperature. The cast structure of the alloy Ti-6Al-4V is generally coarse and has strong solidification texture that leads to inferior properties. Recently, trace boron addition has been reported to produce substantial refinement in cast microstructure for Ti-6Al-4V. Significant improvements in some of the mechanical properties have been reported for the Ti-6Al-4V-0.1B alloy in the as-cast condition. The reasons for microstructural refinement in the boron modified alloy and associated improvements in properties, however, needs to be investigated since the property attributes strongly depend on finer microstructural details including crystallographic texture. In addition, the titanium alloys are processed through thermo-mechanical treatments that involve deformation and annealing response of the alloy. The effect of boron modification on the processing response during thermo-mechanical treatments (TMP) has also not been studied. All these aspects shape the framework of the thesis, wherein microstructure and texture evolution is probed from starting cast condition through different stages of TMP. Micro-mechanisms are identified at every stage from the interrelation of these two intrinsic factors. In the first part of the study, the spatial variation of microstructure and texture in the cast ingot has been studied using SEM-EBSD technique. It has been found that trace boron addition (0.1 wt%) to Ti-6Al-4V alloy ensures excellent microstructural homogeneity throughout the cast ingot. A subdued thermal gradient due to constitutional undercooling persists during solidification and maintains equivalent β grain growth kinetics at different locations in the ingot. For Ti-6Al-4V-0.1B alloy, both high temperature β and room temperature α phase textures weaken. The microstructural attributes of boron addition manifests as the absence of grain boundary α-phase and the presence of TiB particles. Both these features strongly affect the mechanism of β→α phase transformation and consequently weaken the α phase texture. The evolution of microstructure and texture during β-processing of Ti-6Al-4V-0.1B alloy is examined in the second part of the work. Boron modified alloy shows the typical features of β worked microstructure with fine prior β grains, however without the formation of shear bands, which is generally observed in the microstructure of β worked Ti-6Al-4V alloy. The transformed α texture is almost same for the two alloys indicating similarity in the transformation behaviour of boron modified and boron free Ti-6Al-4V alloy due to complete dynamic recrystallization during β processing. The microstructural features as well as the crystallographic texture indicates dominant grain boundary sliding for the boron added alloy which leads to homogeneous deformation response without instability (shear band) formation. In the third part of the study, the deformation response in the (α+β) regime has been studied by carrying out hot compression tests at different temperature under constant true strain rate to simulate experimental processing conditions for the cast Ti-6Al-4V-0.1B alloy. The critical combinations of temperature and strain rate suitable for processing are identified based on flow curves and kinetic analyses. Microstructural features display dynamic recovery of the α-phase at low temperatures and softening due to globularization and/or dynamic recrystallization at high temperatures irrespective of boron addition. The transition temperature for the two mechanisms is comparatively lower for boron added alloy. Unlike Ti-6Al-4V, no sign of instability formation has been observed in Ti-6Al-4V-0.1B. The absence of macroscopic instabilities and early initiation of softening mechanisms has been attributed to microstructural features and texture of boron modified alloy in the initial as-cast condition. In the fourth part, the large strain deformation response has been studied for the Ti-6Al-4V-0.1B alloy by rolling in the (α+β) regime. Microstructure in near α rolling regime is characterized by a few kinked and bent α colonies while others are elongated along the rolling direction. Dynamic softening at higher temperatures is more dominant for the boron added alloy. Microstructural features are strongly orientation sensitive while relative differences are inherited from the starting cast alloys. Texture evolution, however, does not markedly vary for the two alloys and indicates little difference in the slip based deformation processes under plane strain condition. The influence of transformation texture appears early for the boron added alloy and affects the final texture in much stronger way at higher temperature. Subsequent to the (α+β) rolling, static annealing of warm rolled alloys has been carried out. A faster annealing kinetics for boron added alloy has been observed, which is related to deformation prior to annealing leading to additional diffusion pathways due to microstructural factors. Texture of the annealed material is similar to the deformed state for shorter annealing times but substantially modifies by epitaxial growth of primary α phase during long time annealing. The final part of the work deals with the deformation response of boron added alloy under superplastic conditions. Out of the two alloys with similar microstructure and texture, higher elongation for boron modified alloy is justified by the absence of slip based deformation and improved grain boundary sliding. Increase in α/β interfaces due to globularization during warm rolling and static annealing contribute to the grain boundary sliding. The outcomes of the thesis have been presented as a summary at the end and suggestions have been made indicating the scope for future investigations pertaining to this area.

Orientador: Ana Paula Rosifini Claro / Resumo: Dentre os materiais utilizados em aplicações biomédicas, o titânio e suas ligas apresentaram destaque devido a suas excelentes propriedades de volume, como por exemplo, resistência mecânica. No entanto, essas propriedades estão diretamente ligadas à microestrutura, que estão diretamente relacionadas com o seu processamento. O objetivo deste trabalho foi avaliar a influência da deformação plástica severa por Equal Channel Angular Presssing (ECAP) na microestrutura e propriedades mecânicas da liga experimental Ti25Ta25Nb3Sn. Os lingotes da liga Ti25Ta25Nb3Sn foram processados em forno de fusão a arco voltaico com atmosfera controlada e submetidos a tratamento térmico de homogeneização para posterior forjamento a frio. Para o processamento por ECAP os lingotes foram previamente tratados por solubilização. Uma matriz com canal de 90º foi utilizada no processamento por ECAP, seguindo a rota Bc, processando o material com 2 e 4 passes. A morfologia, composição e estrutura foram investigadas usando microscopia eletrônica de varredura, microscopia eletrônica de transmissão e análise por EBSD. As análises de microscopia e EBSD mostraram uma estrutura com uma mistura de grãos refinados e grãos grosseiros após 2 passes e uma homogeneidade maior de grãos refinados após 4 passes. A difração de Raios X indicou a formação da fase α'' e β após 2 passes do processamento por ECAP e após 4 passes apenas a fase β estava presente na estrutura. / Doutor

The current study focuses on phase stability and evolution in the titanium-zinc titanium-copper and titanium-antimony systems. The study utilized the Laser Engineering Net Shaping (LENS™) processing technique to deposit compositionally graded samples of three binary system in order to allow the assessment of phase stability and evolution as a function of composition and temperature the material is subjected to. Through LENS™ processing it was possible to create graded samples from Ti-xSb (up to 13wt%) and Ti-xCu (up to 16wt%). The LENS™ deposited gradient were solutionized, and step quenched to specific aging temperature, and the resulting microstructures and phase were characterized utilizing XRD, EDS, SEM, FIB and TEM. The Ti-Zn system proved incapable of being LENS™ deposited due to the low vaporization temperature of Zn; however, a novel processing approach was developed to drip liquid Zn onto Ti powder at temperatures above β transus temperature of Ti (882 ◦C) and below the vaporization temperature of Zn (907 ◦C). The product of this processing technique was characterized in a similar way as the graded LENS™ depositions. From measurements performed on Ti-Sb it seems that Sb could be a potential α stabilizer in Ti due to the presence of a mostly homogeneous α grains throughout the gradient; however, from XRD it can be understood that a titanium antimonide phase is present. From results obtained from the Ti-Zn samples, it can be surmised that the eutectoid reaction seems to be active, i.e. The eutectoid reaction is kinetically fast, as concluded by the presence of pearlitic structures. Finally, for the Ti-Cu system this work has been attempted to prove or disprove the existence of the Ti3Cu through the use of XRD and TEM SAD patterns. From XRD spectra collected there are peaks belonging to the Ti3Cu orthorhombic phase along with Ti2Cu and α-Ti phase. In addition to the Ti-Cu system displayed structures associated with divorced eutectoid decomposition mechanism, and at low undercooling seems to be prone to forming solid state dendrites.

The main goal of this work is the analysis of manufacturing costs for the component of wheel´s blower. Followed by setting up the size of specific cutting force for milling operation of the titanium alloy Ti-Al6-Mo2-Cr2-Fe-Si, the used tool was a milling cutter which is made out of sintered carbide with conical and spherical face. The final values which are at intervals of 1500 to 1800 MPa were compared with the values of the Sandvik Coromant firm kc = 1690 MPa, for titanium alloy with the strenght in tension Rm = 1050 MPa.

The aim of the thesis is to analyze the production costs and optimize cutting conditions for high-feed face milling of titanium alloy Ti6Al4V. In the experiment were changed cutting conditions, such as cutting speed vc and feed speed vf. During the experiment were checked cutting forces by dynamometr. Furthermore, surface roughness and tool wear is observed.

This diploma thesis studies the machining of group S materials. In the theoretical part of this thesis these materials were divided into groups and subsequently analyzed. These materials were also analyzed in terms of their impaired machinability. In the practical part of this thesis experimental tests were conducted to determine tool life, tool wear and in the case of testing titanium alloy surface roughness too.

Résumé confidentiel. Non communicable / Résumé confidentiel. Non communicable

Advanced glycation end products (AGEs) irreversibly cross-link proteins with sugars and accumulate at a higher age and in diabetes, processes which can interfere with the integration of implants into the tissue. Glyoxal is a highly reactive glycating agent involved in the formation of AGEs and is known to induce apoptosis, as revealed by the upregulation of caspase-3 and fractin (caspase-3 being a key enzyme activated during the late stage of apoptosis and fractin being a caspase-cleaved actin fragment). In this study, we investigated the influence of collagen type I coating on the cytotoxic effect of glyoxal on rat calvarial osteoblastic cells and on human osteosarcoma cells (Saos-2) grown on titanium alloy, Ti6Al4V. Activation of caspase-3 and fractin was measured by counting immunohistochemically stained cells and by flow cytometry with propidium iodide (detection of the apoptosis indicating a sub-G1 peak). Our results showed an increased number of apoptotic osteoblasts after incubation with glyoxal on Ti6Al4V discs. However, the number of apoptotic cells on collagen-coated titanium was significantly smaller than on uncoated titanium after the same treatment. The present findings demonstrate that osteoblasts treated with glyoxal undergo apoptosis, whereas collagen type I coating of titanium alloys (used for implants) has an antiapoptotic function. / Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

Die vorliegende Dissertation beschäftigt sich mit der Untersuchung des Ermüdungsverhaltens einer neu entwickelten Ti-40(wt%)Nb Legierung für die Anwendung als Implantatwerkstoff aus der Materialklasse der β-Titanlegierungen. Darüber hinaus werden auch vergleichende Ermüdungsuntersuchungen zu den Werkstoffen Ti-45(wt%)Nb als weitere binäre β-Titanlegierung sowie an α-Titan als klassischem Referenzwerkstoff im industriellen Einsatz durchgeführt. Ziel ist es, grundlegende Erkenntnisse zu den zyklischen Verformungsmechanismen binärer Ti-Nb Legierungen in Abhängigkeit ihres Werkstoffzustandes und damit Ihrer Mikrostruktur zu erhalten. Im Vergleich mit anderen Implantatwerkstoffen soll daraus eine mögliche Eignung für den Einsatz als nicht resorbierbares Osteosynthesematerial abgeleitet werden. Als übergeordnetes Ziel wird hierbei eine Minimierung des Elastizitätsmodules bei gleichbleibend hohen statischen und zyklischen Festigkeiten angestrebt, um einerseits schnellere Heilungserfolge zu erzielen als auch eine möglichst dauerhafte Implantatzuverlässigkeit zu gewährleisten. Für diesen Zweck wurden umfangreiche Ermüdungsprüfungen an Werkstoffproben und Osteosyntheseplatten in Abhängigkeit von Werkstoff, Mikrostruktur, Oberfläche, Umgebung und Geometrie durchgeführt. Mit Hilfe von strukturanalytischen Verfahren vor und nach der Werkstoffermüdung wurden diese begleitend detailliert charakterisiert. Insbesondere die Ergebnisse zum Einfluss des Werkstoffzustandes von Ti-40Nb erbrachten hierbei direkte Unterschiede und eine um ca. 30 % höhere Schwingfestigkeit im ausgelagerten Zustand aufgrund von vorliegenden isothermen Ausscheidungen der ω-Phase. Zurückgeführt wurde diese Erhöhung zum einen auf einen dominanten Effekt der Ausscheidungshärtung sowie die Unterdrückung von einer in binären Ti-Nb Legierungen möglichen Phasenumwandlung während der zyklischen Belastung. Stattdessen wurden nur im Ermüdungsrissbereich den Gleitbändern ähnliche Deformationsbänder (DB’s) beobachtet, die als ω-verarmte Versetzungskanäle die plastische Verformung tragen, während im rekristallisierten Zustand eine nahezu komplette Transformation in die martensitische α‘‘-Phase infolge der Ermüdung generiert wird. Der Einfluss der Oberfläche wird hierbei als signifikant herausgestellt, da vor allem Kerbeffekte die erreichbaren Schwingfestigkeiten der untersuchten Ti-Nb Legierungen massiv beeinflussen und zum vorzeitigen Versagen führen. Ein überlagerter Geometrieeinfluss, wie im Fall untersuchter Osteosyntheseplatten, hat einen zusätzlichen dominanten negativen Effekt auf das Ermüdungsverhalten. Ein negativer Einfluss eines korrosiven Umgebungsmediums am Beispiel einer Lösung aus simulierter Körperflüssigkeit (SBF) kann hingegen nicht festgestellt werden, was auf die exzellenten Selbstpassivierungseigenschaften von β-Titanlegierungen auf Ti-Nb Basis zurückgeführt wird. Insgesamt ergibt sich auf Grundlage der Ergebnisse dieser Arbeit eine nur bedingte Einsatzfähigkeit als Werkstoff für die Osteosynthese. Vorteile, wie der sehr geringe Elastizitätsmodul und die exzellente Widerstandfähigkeit gegen Korrosionsermüdung stehen einer allgemein nur ausreichenden Schwingfestigkeit sowie hoher Empfindlichkeit für Kerbeffekte jeglicher Art gegenüber. Eine effiziente Ausnutzung der Auslagerungseffekte sowie eine Oberflächennachbehandlung auf Basis von Druckeigenspannungen bieten jedoch weiteres hohes Potential für das Ermüdungsverhalten binärer Ti-Nb Legierungen. / Present thesis investigates the fatigue behavior of a newly developed Ti-40(wt%)Nb alloy from the material class of β-titanium alloys for application as implant material. Furthermore it investigates the fatigue behavior of the binary β-titanium alloy Ti-45(wt%)Nb and α-titanium as standard material already in industrial application for reference. Main focus are the detection of cyclic deformation mechanisms in dependence of material condition and the underlying microstructure. In comparison with other implant alloys, suitability of the new Ti-40Nb alloy as osteosynthesis material shall be evaluated. The overall aim is thereby the minimization of the Young’s modulus with simultaneously high values of static and cyclic strength for better healing chances and long term implant reliability. For this objective, comprehensive fatigue testing on material samples as well as osteosyn-thesis plates was carried out in dependence of material, microstructure, surface, environ-ment and sample geometry. Detailed structural analyses were additionally carried out be-fore and after fatigue testing. Compared with the recrystallized condition of the Ti-40Nb al-loy, fatigue results of the aged condition with present isothermal ω-precipitates in the β-matrix show a 30% higher fatigue strength. Uncovered reasons for this behavior are a domi-nant effect of precipitation hardening as well as the complete suppression of for β-titanium alloy commonly observed phase transformations during fatigue. Whereas the recrystallized condition of the Ti-40Nb alloy is characterized by significant martensitic α’’-phase formation and occasional mechanical twin development during fatigue, the aged condition shows none of these characteristics. Instead deformation bands (DB’s), similar to commonly overserved slip bands during fatigue, are detected in the immediate area of the fatigue crack. These localized DB’s carry all of the plastic deformation in the aged condition of the Ti-40Nb alloy as ω-depleted dislocation channels. Furthermore, the influence of the surface condition regarding the fatigue properties is sig-nificant. The reason are notch effects leading to localized stress concentration and early fa-tigue failure. Tests on the osteosynthesis plates show in addition a superimposed effect of the geometry, which leads to an even more decreased fatigue strength of Ti-40Nb and the reference α-titanium. A negative influence of corrosion fatigue in simulated body fluid (SBF) is on the contrary not detected, which is caused by the excellent self-passivating properties of β-titanium alloys on the basis of Ti-Nb. An overall evaluation of the material leads to an only limited suggestion as osteosynthesis material. Advantages are the very low Young’s modulus and the excellent corrosion fatigue resistance. Disadvantages are the only insufficient fatigue strength compared to other standard implant materials and the high susceptibility for notch effects leading to a rapid decrease of fatigue strength. Nevertheless, an efficient use of the positive effects of the aged condition as well as a surface post-treatment to induce positive residual compression stresses provide high potential for Ti-40Nb or the binary Ti-Nb alloys in general.