Le présent travail concerne l’étude de l’usinage de l’alliage de titane Ti-6Al-4V, matériau très apprécié par les industries aéronautique, biomédicale et de l’énergie. Les qualités des alliages de titane sont nombreuses : haute résistance aux températures élevées et à la corrosion, haute résistance mécanique, biocompatibilité, etc. Cependant, certaines propriétés physiques de ces matériaux, comme leur faible conductivité thermique, conduisent à des difficultés lors de leur mise en forme par usinage. Des études ont été et sont toujours conduites afin de comprendre le comportement de ces matériaux lors de leur mise en forme. Peu de travaux portent sur la prise en compte de la microstructure dans le comportement des alliages de titane lors du procédé d’usinage. Cette dimension constitue l’une des originalités de ce travail de thèse. Les phénomènes microstructuraux sont caractérisés à travers une étude expérimentale en coupe orthogonale de l’alliage Ti-6Al-4V. Les efforts, la température, la morphologie des copeaux et la microstructure sont analysés et interprétés. Une étude numérique du processus de coupe par simulation éléments finis est employée pour comprendre le rôle de l’endommagement et de la recristallisation. A partir des conclusions de ces différentes études, la construction d’un nouveau modèle de comportement est proposée. Ce modèle est appliqué à une modélisation élément fini pour différentes conditions de coupe afin d’étudier l’influence des paramètres d’usinage. Le modèle est validé par comparaison aux résultats expérimentaux. Il est ensuite exploité afin de proposer une analyse du processus de la coupe et notamment de la formation du copeau. / The present work concerns the study of the machining of titanium alloy Ti-6Al-4V. This material is much appreciated by the aerospace, biomedical and energy industries for its advantageous properties: high resistance to high temperatures and corrosion, high mechanical strength, biocompatibility, etc. However, certain physical properties of these materials, such as their low thermal conductivity, lead to difficulties during the machining process. Studies have been and are still conducted to understand the behavior of these materials during their shaping. Few studies consider the influence of microstructure on the behavior of titanium alloys during the machining process. This is one of the originalities of the present work. The microstructural phenomena are characterized through an experimental study of orthogonal cutting of the Ti-6Al-4V alloy. Machining forces, temperature, chip morphology and microstructure are analyzed and discussed. A numerical study of the finite element simulation process is used to understand the role of damage and recrystallization. From the conclusions of these different studies, the construction of a new model of behavior is proposed. This model is applied to finite element modeling for different cutting conditions to study the influence of machining parameters. The model is validated by comparison with the experimental results. It is then used to propose an analysis of the microstructural phenomena during the cutting process and the formation of the chip.

O uso de metais na fabricação de implantes ortopédicos iniciou-se nas primeiras décadas do século XX. O aumento do uso de biomateriais implantáveis aumentam também os casos de infecção. A colonização da superfície do biomaterial pode ter início no momento da inserção do corpo estranho no organismo e geralmente é causada por microrganismos da microbiota da pele ou região adjacente ao implante. Este estudo teve por objetivo avaliar por métodos microbiológicos e microscópio eletrônico de varredura (MEV), a aderência bacteriana à superfície de aço inoxidável e liga de titânio de uso médico, bem como a molhabilidade da superfície destes metais. As bactérias usadas foram Staphylococcus epidermidis ATCC 12228 e Staphylococcus aureus ATCC 25923. Os discos de aço inoxidável (15,0 mm de diâmetro x 2,0 mm de espessura) e de liga de titânio (12,0 mm de diâmetro x 2,0 mm de espessura) foram inseridos, asséptica e separadamente, em tubos contendo 15,0 mL de caldo Mueller Hinton e 200,0 \'mü\'L de suspensão bacteriana da ordem de \'10 POT.8\' UFC/mL. Cada bactéria foi estudada individualmente. Os tubos foram incubados por 1, 6, 24, 48 e 72 horas sob agitação a 37 graus Celsius. Após os períodos de incubação, os discos foram retirados do caldo de cultura e submetidos ao banho de ultrassom em 5,0 mL de solução fisiológica 0,85% esterilizada. Deste líquido, foram realizadas diluições da ordem de \'10 POT.-1\' a \'10 POT.-4\' para a quantificação de células viáveis. Os valores foram expressos em UFC/mL. Para S. epidermidis sobre a liga de titânio, o número de células viáveis foi em 1 hora: 7,20 x \'10 POT.4\'; 6 horas: 3,90 x \'10 POT.6\'; 24 horas: 3,80 x \'10 POT.6\'; 48 horas: 9,70 x \'10 POT.6\' e 72 horas: 1,00 x \'10 POT.7\'. Sobre o aço inoxidável, o número de células viáveis foi em 1 hora: 3,00 x \'10 POT.3\'; 6 horas: 2,90 x \'10 POT.6\'; 24 horas: 3,20 x \'10 POT.6\'; 48 horas: 1,41 x \'10 POT.7\' e 72 horas: 1,88 x \'10 POT.7\'. Para S. aureus ) sobre a liga de titânio, o número de células viáveis foi em 1 hora: 2,00 x \'10 POT.3\'; 6 horas: 1,00 x \'10 POT.4\'; 24 horas: 3,10 x \'10 POT.4\'; 48 horas: 4,30 x \'10 POT.4\' e 72 horas: 5,80 x \'10 POT.3\'. Sobre o aço inoxidável, o número de células viáveis foi em 1 hora: 6,00 x \'10 POT.3\'; 6 horas: 2,00 x \'10 POT.3\'; 24 horas: 1,50 x \'10 POT.4\'; 48 horas: 3,20 x \'10 POT.5\' e 72 horas: 6,00 x \'10 POT.3\'. Ambas as superfícies metálicas foram caracterizadas como de média molhabilidade, onde a liga de titânio teve média \'+ OU -\' desvio padrão de 39,016 \'+ OU -\' 11,267 e o aço inoxidável 58,083 \'+ OU -\' 7,165. Tanto o S. aureus quanto o S. epidermidis aderiram às superfícies dos biomateriais estudados, como foi observado por meio de MEV. Com base nos resultados é possível concluir que os dois microrganismos são capazes de aderir a superfícies metálicas. Isto aumenta a preocupação quanto à patogênese das infecções relacionadas a implantes ortopédicos, uma vez que esses microrganismos estão presentes na pele humana e oferecem o risco de reações inflamatórias e infecção, promovendo a perda do implante para efetivar a cura. / The utilization of metals in the manufacture of orthopedic implants started in first decades of twentieth century. The increased use of implantable biomaterials increased also infection cases. Biomaterial surface colonization can start at the moment of foreign body insertion in the organism and is usually caused by microorganisms of skin microbiota or adjacent region to the implant. This study aimed to evaluate microbiological methods and scanning electron microscopy (SEM), the bacterial adhesion to surface of stainless steel and titanium alloy of medical use, as well as the surface wetability of these metals. The used bacteria were Staphylococcus epidermidis ATCC 12228 and Staphylococcus aureus ATCC 25923. The stainless steel (15,0 mm diameter x 2,0 mm thick) and titanium alloy (12,0 mm diameter x 2,0 mm thick) discs were inserted, aseptic and individually, into tubes containing 15,0 mL Mueller Hinton broth and 200,0 \'mü\'L of bacterial suspension with \'10 POT.8\' CFU/mL concentration. Each bacterium was individually studied. The tubes were incubated for 1, 6, 24, 48 and 72 hours under agitation at 37 Celsius degrees. After incubation periods, the discs were removed from culture broth and submitted to the ultrasound bath in 5,0 mL of sterile saline. From this liquid were realized dilutions of \'10 POT.-1\' to \'10 POT.-4\' to quantify the viable cells. Values were expressed in CFU/mL. S. epidermidis over titanium alloy viable cells number was in 1 hour: 7,20 x \'10POT.4\'; 6 hours: 3,90 x \'10 POT.6\'; 24 hours: 3,80 x \'10 POT.6\'; 48 hours: 9,70 x \'10 POT.6\' and 72 hours: 1,00 x \'10 POT.7\'. Over stainless steel viable cells number was in 1 hour: 3,00 x \'10 POT.3\'; 6 hours: 2,90 x \'10 POT.6\'; 24 hours: 3,20 x \'10 POT.6\'; 48 hours: 1,41 x \'10 POT.7\' and 72 hours: 1,88 x \'10 POT.7\'. To S. aureus over titanium alloy viable cells number was in 1 hour: 2,00 x \'10 POT.3\'; 6 hours: 1,00 x \'10 POT.4\'; 24 hours: 3,10 x \'10 POT.4\'; 48 hours: 4,30 x \'10 POT.4\' and 72 hours: 5,80 x \'10 POT.3\' and over stainless steel viable cells number was in 1 hour: 6,00 x \'10 POT.3\'; 6 hours: 2,00 x \'10 POT.3\'; 24 hours: 1,50 x \'10 POT.4\'; 48 hours: 3,20 x \'10 POT.5\' and 72 hours: 6,00 x \'10 POT.3\'. Both metal surfaces were characterized as medium wetability, where the contact angle of titanium alloy was mean \'+ OU -\' standard deviation 39,016 \'+ OU -\' 11,267 and stainless steel 58,083 \'+ OU -\' 7,165. Both S. aureus as S. epidermidis adhered to surfaces of biomaterials studied, as observed by SEM. Based on the results we concluded that two microorganisms are able to adhere to metal surfaces. This increases the concern about the pathogenesis of infections related to orthopedic implants, since these microorganisms are present in human skin and provide the risk of infection and inflammatory reactions, furthering implant loss to effective cure.

O presente trabalho teve como objetivo principal avaliar o efeito dos recobrimentos TiN e TiAlN depositados por PVD a plasma na liga Ti-6Al-4V sob condições de fluência a 600 °C e corrosão em meios contendo cloreto a 25, 60 e 80 °C. O trabalho foi complementado com análises microestruturais e dos revestimentos superficiais utilizando-se as técnicas de difração de raios X, microscopias óptica, eletrônica de varredura e de transmissão, medidas de microdureza e oxidação isotérmica. Os resultados permitiram concluir que a liga Ti-6Al-4V constituída pela configuração de Widmanstätten apresentou dureza média de 343 HV para a condição como recebida. Após os tratamentos por PVD a plasma observou-se um recobrimento à base de TiN de espessura de 2,2 ?m e composição igual a Ti0,7N. O recobrimento a base de TiAlN/TiAlCrN apresentou espessura em torno de 6 ?m e composição igual a (Ti0,38Al0,62)N/(Ti0,31Al0,50Cr0,19)N. As medidas do potencial em circuito aberto e polarização mostraram que a liga Ti-6Al-4V apresentou comportamento ativo com transição ativo-passiva em solução HCl e comportamento passivo em solução NaCl a 25, 60 e 80 °C. As amostras recobertas por TiN e TiAlN/TiAlCrN apresentaram comportamento passivo nas duas soluções corrosivas e em todas as temperaturas estudadas. A amostra revestida por TiN depositado por PVD apresentou os menores valores de taxa secundária em fluência para tensões maiores que 222 MPa, contudo a amostra nitretada a plasma apresentou maiores valores de vida útil e níveis de ductilidade. A análise conjunta dos expoentes de tensão, energia de ativação e estrutura de discordâncias indicaram que o principal mecanismo de deformação por fluência foi controlado por escalagem de discordâncias. O cálculo do parâmetro de tolerância ao dano (W) contribuiu para indicar que os revestimentos TiN e TiAlN/TiAlCrN, apesar de protegerem a superfície da oxidação, diminuíram a capacidade de deformação plástica ao longo do estágio terciário e vida útil da liga Ti-6Al-4V, reduzindo a ductilidade. Finalmente, os tratamentos superficiais utilizados neste trabalho foram eficientes por seu efeito de proteção através da deposição de um elemento cerâmico mais estável na superfície e não por transformações causadas na microestrutura. / This study aimed to evaluate the effect of the plasma-assisted PVD TiN and TiAlN/TiAlCrN coatings in the Ti-6Al-4V alloy under creep conditions at 600 °C and under corrosion conditions in environments containing chloride at 25, 60 and 80 °C. The study was complemented by microstructural and surface coatings analysis using XRD, optical, scanning and transmission electron microscopy, microhardness and isothermal oxidation. The results showed that the Ti-6Al- 4V alloy with Widmanstätten morphology presented an average hardness of 343 HV for as received condition. After treatment by plasma PVD, it was observed a TiN based coating, with 2,2 ?m and composition of Ti0,7N. The TiAlN/TiAlCrN based coating presented 6 ?m of thickness and composition of (Ti0,38Al0,62)N/(Ti0,31Al0,50Cr0,19)N. Anodic polarization and open circuit potential showed that Ti-6Al-4V alloy had active behavior with active - passive transition in HCl solution and passive behavior in NaCl solution at 25, 60 and 80 °C. The TiN and TiAlN/TiAlCrN coated samples showed passive behavior in both corrosive solutions and at all studied temperatures. The TiN coated sample showed the lowest values of secondary creep rate for stresses greater than 222 MPa, however, the plasma nitrided sample showed higher levels of service life and ductility. The analysis of stress exponents, activation energy and dislocations structures indicated that the main mechanism of creep was controlled by climbing dislocations. The damage tolerance parameter (W) calculation contributed to indicate that TiN and TiAlN/TiAlCrN coatings, although protect the surface from oxidation, decreased plastic deformation ability throughout tertiary stage and service life of the Ti-6Al-4V alloy, decreasing ductility. Finally, the surface treatments, used in this study, were efficient for their protective effect by depositing a more stable ceramic compound on surface and not by transformations caused on microstructure.

Les biomatériaux en titane sont de plus en plus utilisés dans les implants dentaires et les prothèses de hanche. Toutefois, la surface des implants de titane doit être modifiée pour devenir davantage bioactive. Dans cette étude, les substrats de Ti-6Al-4V ont été d'abord modifiés par un traitement mécanique, puis par un traitement acide. Dans un deuxième temps, les échantillons ont subi un traitement alcalin dans une solution de NaOH puis un traitement thermique, ce qui a provoqué la formation d'une couche de titanate de sodium sur leur surface. Enfin, du phosphate de calcium a été déposé soit par voie sol-gel, soit par voie autocatalytique, sur la couche de titanate de sodium pour obtenir un revêtement bioactif de titanate de sodium/ phosphate de calcium.Après le dépôt, la morphologie et la structure de la couche de phosphate de calcium ont été analysées par diverses méthodes comme FTIR, Raman, ORX, MES, MET, EDS-X et SAED. De plus, la coupe transversale du revêtement de titanate de sodium/ phosphate de calcium a été analysée par MEB/ EDS-X. Et l'adhésion du dépôt de phosphate de calcium au substrat a été qualitativement estimée par nano-indenteur. La bioactivité in vitro du dépôt a été vérifiée par la méthode de Kokubo utilisant la solution simulant le plasma sanguin (SBF). Et la cytotoxicité in vitro du dépôt a été vérifiée par le test de viabilité cellulaire utilisant les ostéoblastes MG63. Les résultats ont indiqué que le dépôt de phosphate de calcium est cytocompatible et bien lié au substrat. De plus, le dépôt de phosphate de calcium est stable en milieu physiologique (SBF) pour des durées d'immersion de 2 à 28 jours. La croissance d'apatite sur la surface des dépôts a été observée après 2 jours d'immersion dans SBF. / Titanium and its alloys based biomaterials are more and more used for medical implants in reconstructing of failed tissue. However to respond to the demand of orthopaedic and dental application, their surfaces have to be modified to increase the osteointegration rate. ln this study, the Ti-6Al-4V alloy surface was firstly mirror polished and treated by an acid solution. Then, a thin film of sodium titanate was formed on its surface via an alkaline-heat treatment. Finally, a calcium phosphate was coated on the sodium titanate layer by using the sol-gel technique or the autocatalytic route. By this process, a bi-phase bioactive sodium titanate/calcium phosphate layer was created on the titanium substrate.After coating, the morphology and the structure of calcium phosphate layer were analyzed by various methods such as FTIR, Raman, XRD, SEM, TEM, EDS-X and SAED. Additionally, a cross-section view of sodium titanate/ calcium phosphate layer was also realized by SEM/ EDS-X.And the adhesion of calcium phosphate layer onto the substrate was verified qualitatively by nano-indenter. The in vitro bioactivity of calcium phosphate coated samples was tested by Kokubo's method using the simulated body fluid (SBF). The in vitro cytotoxicity of calciumphosphate coated samples was estimated by cell viability assay using the osteoblasts MG63.The results showed that the calcium phosphate coating is cytocompatible and strongly bonds to the substrate. ln addition, the calcium phosphate coating was stable in SBF for different soaking periods from 2 to 28 days. And the growth of apatite on the calcium phosphate coated sample surface was identified after 2 days of immersion in SBF.

The alloys of Ti are extensively used in a number of industries with the α+β alloy Ti-6Al-4V (referred to as Ti64 hereafter) being the most popular. Recently, it was demonstrated that the addition of a small amount of B – as small as 0.04 wt.% – results in an order-of-magnitude reduction in the as-cast grain size. Consequently, there is considerable current interest in understanding the mechanical behaviour of B-modified alloys, with particular emphasis on correlating the microstructural changes with the property variations and the deleterious effects – if any – of TiB particles especially in the context of fatigue. Prior studies have indicated that the addition of 0.1 wt.% B to Ti64 yields the most optimum combination of room temperature properties. The research reported in the current thesis builds further on it, with the objective of exploring the utility of Ti64-B alloys in the engineering applications context. Towards this end, mechanical behaviour of cast and wrought Ti64-B alloys at cryogenic and high temperatures, the possible effect of hydrogenation on the tensile properties, and strain-controlled low cycle fatigue was experimentally evaluated as detailed below. While extensive work is reported on as-cast alloys, the mechanical properties of wrought alloys have not been examined hitherto. Keeping this in view, room temperature tensile and fatigue properties of wrought Ti64-B alloys were investigated. Microstructures of wrought alloys show kinking of the  lamellae and alignment of TiB particles along the flow direction. Marginal enhancement in tensile and fatigue properties upon forging is noted. Decrease in fatigue strength of wrought Ti64-0.04B is observed due to increase in volume fraction of the grain boundary α phase with B addition, which acts as a crack nucleation site. No significant effect of TiB particles on tensile and fatigue properties is observed. Next, strain-controlled fatigue behaviour was investigated. Results show significant softening when the strain amplitudes, ΔεT/2, are ≥0.75%. B addition was found to improve the fatigue life for ΔεT/2 ≤ 0.75% as it corresponds to the elastic regime and hence strength dominated. At ΔεT/2 = 1%, in contrast, the base alloy exhibits higher life as TiB particle cracking due to strain incompatibility renders easy crack nucleation in the B-modified alloys. To examined whether the addition of B to Ti64 is beneficial in enhancing its high temperature mechanical behavior, tensile and creep tests are carried out in the temperature range of 475-550 °C. Experimental results show that the B addition enhances both elevated temperature strength and creep properties of Ti64, especially at the lower end of the temperatures investigated. The steady state creep rate in the B-modified alloys were lower than that in the base alloy, and both the strain at failure as well as the time for rupture increases with the B content. These marked improvements in the creep resistance due to B addition to Ti64 were attributed primarily to the increased number of inter-phase interfaces – a direct consequence of the microstructural refinement that occurs with the B addition – that provide resistance to dislocation motion. Titanium alloys are widely used in various ambient and high temperature applications. However, in some instances these alloys are exposed to hydrogen and low operating temperature environments. Ti64 alloy shows poor ductility in hydrogen and cryogenic environments. Whether the microstructural refinement that occurs with the B addition also improves its relative mechanical performance in such environments is examined. For this purpose, alloys were H charged at 500 and 700 °C for up to 4 h. Microstructures and room temperature tensile properties of the resulting alloys have been evaluated. Experimental results show that charging at 700 °C for 2 h leads to the formation of titanium hydride in the microstructure, which in turn causes severe embrittlement. For shorter durations of charging, a marginal increase in strength was noted, which is attributed to the solid solution strengthening by hydrogen. The mechanical performance of the B modified alloys was found to be relatively better, implying that B addition is beneficial in applications that involve H environment. Finally, the utility of B-modified Ti64 for cryogenic applications is examined through notched and unnotched tensile tests at 77 and 20 K. While the addition of B up to 0.3 wt.% increases the strength at both 77 and 20 K. However, the ductility of the alloys decreases drastically with decrease in temperature. The tensile stress-strain responses of Ti64-B alloys exhibit serrations beyond yielding at 20 K. The extent of serrations were found to be maximum in coarse grained B-free Ti64 alloy, while only one serration could be identified in B-containing alloys. Activation of deformation twinning at 20 K results in the formation of serrations. Three twinning modes were identified in coarse grained B-free Ti64 alloy- {10 ̅2}, {11 ̅1} and {5 ̅1 ̅} while only{10 ̅2}twinning mode was activated in B-containing alloys. Extensive deformation through twinning results in higher ductility of B-free Ti64 alloy at 20 K in comparison to B containing alloys.

No description available.

Titanium (Ti) alloys have been commonly used in the aerospace industry, not only because they have a high strength-to-weight ratio (comparing to the steels) but also their satisfactory corrosion resistance. Furthermore, they can be assembled with the carbon fibre composite parts. However, conventional manufacturing methods cause high material scrap rate and require lots of machining to obtain the final shape and size, which increases both the manufacturing time and cost. In order to improve the efficiency and reduce the cost of Ti parts, Additive Manufacturing (AM) has been developed. Rolled Wire and Arc Additive Manufacturing (rolled WAAM) is one of the AM processes. The main characteristics of this technology is the reduced β grain size to refine the alloy's microstructure. Both the ultimate tensile strength and yield strength of Ti alloy made by rolled WAAM are at least 10% higher than traditional wrought Ti. This project is to investigate the fatigue crack growth rates of the Ti-6Al-4V built by rolled WAAM process in both the longitudinal and transverse orientations to study the effect of rolling on fatigue crack growth rate of WAAM processed Ti. The project was carried out by testing the fatigue crack growth rates for 4 compact tension specimens. The test results of different orientations were compared with each other, and scatters in fatigue life and fatigue crack growth rate were found. Fatigue crack growth rate is lower in the longitudinal specimens. The results are also compared with those of the unrolled WAAM specimens tested in a previous project. It was found that rolling can significantly improve the fatigue crack growth behaviour in WAAM processed Ti, and can reduce the difference between the two orientations, i.e. achieving better isotropic material properties. Recorded scatters may be caused by the process induced residual stresses, error in measurement, and the test machine load range being much higher than the applied loads. More specimens can be tested to validate above observations further.

Additive manufacturing (AM) for metals is a manufacturing process that has increased a lot in popularity last few years as it has experienced significant improvements since its beginning, both when it comes to accuracy and deposition rates. There are many different AM processes where the energy sources and deposition methods varies. But the common denominator is their layer wise manufacturing process, melting layer on layer. AM has a great design freedom compared to conventional manufacturing, making it possible to design new structures with decreased weight and increased performance.  A drawback is slow manufacturing speeds, making it more expensive. But when it comes to low lot sizes and complex structures AM is very competitive. So, for the aerospace and space industry AM is a good option as manufacturing cost is less of an issue and where saving weight is of great concern, both environmentally and economically.  There are however many topics left to research before additive manufactured titanium can be widely adopted for critical components, such as microstructure and texture development and its correlation to mechanical properties. The aim of this work has been to investigate the microstructure and texture of various AM processes. Microstructural features such as prior β grains, grain boundary α (GB-α), α laths, α colonies have been characterized along with hardness measurements for 5 different AM processes. Some of these AM processes have also been investigated in the SKAT instrument in Dubna, Russia, to obtain their texture. These textures have then been compared with one another and correlated to previous microstructural investigations and mechanical properties. This is important knowledge as the microstructure and the texture sets the basis for the mechanical properties. In case there is a high texture, the material can have anisotropic mechanical behavior, which could be either wanted or unwanted for different applications.   Some the findings are that α phase was found to increase in the prior β grain boundary for the AM processes with low cooling rates, while it was discontinuous and even non-present for the AM processes with high cooling rates. The prior β size are larger for the directed energy deposition (DED) processes than for the powder bed fusion (PBF) processes. Parallel bands were present for the DED process while being non-present for the PBF processes. Concerning the texture, it was found that LMwD had a higher texture than EBM and SLM. Texture inhomogeneity was also found for the LMwD process., where two parts of the same sample was investigated and the material closer to the surface had higher texture.

Orientador: Vicente Afonso Ventrella / Resumo: O presente trabalho estudou o processo de soldagem laser Nd:YAG pulsado aplicado em lâminas finas da liga de titânio Ti-6Al-4V, utilizado no revestimento de sensores que trabalham em ambiente corrosivo da indústria sucroalcooleira, química, petroquímica e alimentícia. Variou-se a energia de pulso de 1,0 J a 2,00 J, com incrementos de 0,25 J com a velocidade de soldagem de (ν) taxa de repeticao (Rr) fixas de 525mm/min e 39Hz respectivamente e largura temporal de 4 ms. As soldas foram realizadas com proteção gasosa de argônio com vazão de 10 l/min. Os ensaios realizados para a pesquisa foram: análise macrográfica, ensaio de tração e fractografia, ensaio de microdureza e caracterização microestrutural. Para revelação dos detalhes no metal de solda foi utilizado um ataque químico com o reagente Kroll. As medidas de geometria (largura do cordão, largura de união e profundidade) dos cordões de solda, bem como a microestrutura, foram realizadas através de imagens obtidas pelo Microscópio Óptico Neophot 21 e editadas utilizando o software ImageJ. O ensaio de tração foi realizado através de uma Máquina Universal de Ensaios, além do ensaio de microdureza, que foi realizado na escala Vickers. Os resultados obtidos mostraram que o controle da energia do pulso é de fundamental importância para a geração de juntas soldadas adequadas, em processo de soldagem por laser de lâminas finas. Também, os parâmetros geométricos aumentaram em função do aumento da energia de pulso e houve maior formaç... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The present work studied the pulsed Nd: YAG laser welding process applied in thin films of the titanium alloy Ti-6Al-4V, used in the coating of sensors that work in the corrosive environment of the sugar-alcohol, chemical, petrochemical and food industry. The pulse energy was varied from 1.0 J to 2.00 J, with increments of 0.25 J with welding speed (ν) and repetition rate (Rr) fixed in 525 mm / min and 39 Hz respectively and time width of 4 ms. An argon gas protection was used with a flow rate of 10 l / min. The tests carried out for the research were: macrographic analysis, tensile and fracture tests, microhardness test and microstructural characterization. A chemical attack with the Kroll reagent was used to reveal details on the weld bead. Measurements based on bead width, union width and depth of the fusion zone as well as the microstructure were performed using images obtained by the Neophot 21 Optical Microscope and edited using the ImageJ software. The tensile test was performed through a Universal Testing Machine, in addition to the microhardness test, which was performed on the Vickers scale. Results showed that the control of the pulse energy is of fundamental importance for the generation of suitable welded joints, in process of laser welding of thin slides. Also, geometric parameters increased as a function of the increase in pulse energy and there was more formation of the α 'phase (martensite) according to the highest peak energy used. Besides that, microhardnes... (Complete abstract click electronic access below) / Mestre

<p>Aeronautical products additively manufactured by Selective Laser Melting (SLM), are known to have fatigue properties which are negatively impacted by porosity defects, microstructural features and residual stresses. Little research is available studying these phenomena with respect to the short fatigue crack growth (FCG) inconsistency problem, the large focus being on the long FCG. This thesis seeks to add useful knowledge to the understanding of the mechanisms for short crack growth variability in SLM manufactured Ti-6Al-4V, with the two variables for the process conditions and build directions investigated. An in-situ FCG investigation using x-ray synchrotron computed micro-tomography (μXSCT) was used to visually observe and quantify the short crack path evolution. Crack growth, deflections and porosity interactions were noted and discussed in relation to microstructure, build layer thickness and build layer orientation. A novel use of in-situ energy dispersive x-ray diffraction (EDD) was able to show the lattice strains evolving as a propagating crack moved through a small region of interest. The results presented show the ability to reliably obtain all six elastic strain tensor components, and interpret useful knowledge from a small region of interest. </p> <p> </p> <p>There are conflicting views in literature with respect to the damage tolerance behavior of as built SLM manufactured Ti-6Al-4V. In the 2018 review by Agius et al., the more prominent studies were considered with Leuders et al. showing the highest long FCG rates for cracks parallel to the build layer and Cain et al. showing cracks propagating through successive build layers as highest [1]–[3]. Cain et al. and Vilaro et al. report significant anisotropy in long FCG for different build orientations whereas Edwards and Ramulu present similar FCG behavior for three different build directions [2]–[5]. Kruth et al. concluded that for optimized build parameters without any (detectable) pores, the building direction does not play a significant role in the fracture toughness results [6]. All of the mentioned literature reported martensitic microstructures and the presence of prior grain structures for as built SLM Ti-6Al-4V.</p> <p> </p> <p>No studies to the authors knowledge have considered the short FCG of SLM manufactured Ti‑6Al‑4V and its implications to the conflicting damage tolerance behaviors reported in literature [1]. In this work small cross-sectional area (1.5 x 1.5 ) samples in two different build conditions of as built SLM Ti-6Al‑4V are studied. The short FCG rate of three different build directions was considered with cracks parallel to the build layers shown to be the most damaging. The microstructure and build layer are shown to be the likely dominant factors in the short FCG rate of as built Ti-6Al-4V. In terms of porosity, little impact to the propagating short crack was seen although there is local elastoplastic behavior around these defects which could cause toughening in the non-optimized build parameter samples tested. The fracture surfaces were examined using a Scanning Electron Microscope (SEM) with the results showing significant differences in the behavior of the two build conditions. From the microindentation hardness testing undertaken, the smooth fracture surface of the optimized sample correlated with a higher Vickers Hardness (VH) result and therefore higher strength. The non-optimized samples had a ‘rough’ fracture surface, a lower VH result and therefore strength. Furthering the knowledge of short FCG in SLM manufactured Ti-6Al-4V will have positive implications to accurately life and therefore certify additive manufactured aeronautical products.</p>