Добірка наукової літератури з теми "Ti6Al4V joining"

Hybrid lightweight components with strong and reliable bonding qualities are necessary for practical applications including in the automotive and aerospace industries. The direct laser joining method has been used to produce hybrid joints of Ti6Al4V and glass fiber reinforced polyamide (PA66-GF30). Prior to the laser joining process, a surface texturing treatment is carried out on Ti6Al4V to improve joint strength through the formation of interlock structures between Ti6Al4V and PA66-GF30. In order to reduce the generated micro-pores in Ti6Al4V-PA66-GF30 joints, a modified laser joining method has been proposed. Results show that only very few small micro-pores are generated in the joints produced by the modified laser joining method, and the fracture strength of the joints is significantly increased from 13.8 MPa to 41.5 MPa due to the elimination of micro-pores in the joints.

Nano structured surface generation is useful in inducing specific functionalities to the surface. This work attempts on generation of such surface through thermal dewetting. Enhanced adhesion behavior of such surface is utilized for joining MACOR® ceramic to Ti6Al4V alloy. Ti6Al4V alloy is brazed with MACOR® by microwave energy using TiCuSil as a braze alloy. MACOR® ceramic is subjected to pre-treatment called gold dewetting. For comparison plain ceramic is also used for joining. The reaction zone formed on joining Ti6Al4V to gold dewetted MACOR® is more uniform than the untreated MACOR® ceramic interface. Energy Dispersive Spectroscopy (EDS) analysis of the reaction zone suggests the formation of Ti2Cu and Ti3Au intermetallic compounds. The shear strength of the pre-treated samples is observed to be higher than that of plain joints.

Diffusion bonding of Ti6Al4V to Al2O3 using Ni/Ti reactive nanomultilayers as interlayer material was investigated. For this purpose, Ni/Ti multilayer thin films with 12, 25, and 60 nm modulation periods (bilayer thickness) were deposited by d.c. magnetron sputtering onto the base materials’ surface. The joints were processed at 750 and 800 °C with a dwell time of 60 min and under a pressure of 5 MPa. Microstructural characterization of the interfaces was conducted by scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS), and electron backscatter diffraction (EBSD). The mechanical characterization of the joints was performed by nanoindentation, and hardness and reduced Young’s modulus distribution maps were obtained across the interfaces. The joints processed at 800 °C using the three modulation periods were successful, showing the feasibility of using these nanolayered films to improve the diffusion bonding of dissimilar materials. Using modulation periods of 25 and 60 nm, it was also possible to reduce the bonding temperature to 750 °C and obtain a sound interface. The interfaces are mainly composed of NiTi and NiTi2 phases. The nanoindentation experiments revealed that the hardness and reduced Young’s modulus at the interfaces reflect the observed microstructure.

The bioceramic hydroxyapaptie (HA) is frequently used as coat in titanium medical implants improving bone fixation and thus increasing a lifetime of the implant. However, its joining to the titanium alloy is not satisfactorily good. The aim of this work is to produce TiO2and HA gradient coatings on Ti6Al4V alloy to improve the interface joining. Compared the microstructures of cross section of Ti6Al4V-HA coating and Ti6Al4V-TiO2/HA gradient coatings. HA coatings were obtained by sol-gel method with sol solutions prepared from calcium nitrate tetrahydrate and triethyl phosphate as the calcium and phosphorous sources. And TiO2 coatings were obtained from Tetra Butyl Titanate and absolute ethyl alcohol as the sources by sol-gel method too. The configuration and structure were investigated with scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques. The results demonstrated that the TiO2/HA gradient coatings have a homogeneous microstructure. The TiO2coating made the HA coating adhere to the Ti-6Al-4V substrate well.

The dissimilar material joining of aluminum and titanium alloys is recognized as a challenge due to the significant differences in the physical, chemical, and metallurgical properties of these alloys, where the increasing demands for high strength and lightweight alloys in aerospace, defense, and automotive industries. Joining these two alloys using the conventional fusion techniques produces commercially unacceptable sound joints due to irregular, complex weld pool shapes, cracking and low strength, high residual stresses, cracks, and microporosity, and the brittle intermetallic compounds formation leads to poor formability or inferior mechanical properties. The formation of intermetallic compounds is inevitable but it is less severe in solid-state than in the fusion welding process. Hence, this article reviews on aluminum–titanium joining using different solid-state and hybrid joining processes with emphasis on the effect of process parameters of the different processes on the weld microstructure, mechanical properties along with the type of intermetallic compounds and defects formed at the weld interface. Among the various solid-state welding processes for aluminum–titanium joining, the following grades of aluminum and titanium alloys were employed such as cp Ti, Ti6Al4V, cp Al, AA1xxx, AA 2xxx, AA5xxx, AA6xxx, AA7xxx, out of which Ti6Al4V and AA6xxx alloys are the most common combination.

This work aims to investigate the joining of Ti6Al4V alloy to alumina by diffusion bonding using titanium interlayers: thin films (1 µm) and commercial titanium foils (5 µm). The Ti thin films were deposited by magnetron sputtering onto alumina. The joints were processed at 900, 950, and 1000 °C, dwell time of 10 and 60 min, under contact pressure. Experiments without interlayer were performed for comparison purposes. Microstructural characterization of the interfaces was conducted by optical microscopy (OM), scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS), and electron backscatter diffraction (EBSD). The mechanical characterization of the joints was performed by nanoindentation to obtain hardness and reduced Young’s modulus distribution maps and shear strength tests. Joints processed without interlayer have only been achieved at 1000 °C. Conversely, joints processed using Ti thin films as interlayer showed promising results at temperatures of 950 °C for 60 min and 1000 °C for 10 and 60 min, under low pressure. The Ti adhesion to the alumina is a critical aspect of the diffusion bonding process and the joints produced with Ti freestanding foils were unsuccessful. The nanoindentation results revealed that the interfaces show hardness and reduced Young modulus, which reflect the observed microstructure. The average shear strength values are similar for all joints tested (52 ± 14 MPa for the joint processed without interlayer and 49 ± 25 MPa for the joint processed with interlayer), which confirms that the use of the Ti thin film improves the diffusion bonding of the Ti6Al4V alloy to alumina, enabling a decrease in the joining temperature and time.

Additive Manufacturing (AM) for metals includes is a group of production methodst hat use a layer-by-layer approach to directly manufacture final parts. In recent years, the production rate and material quality of additive manufactured materials have improved rapidly which has gained increased interest from the industry to use AM not only for prototyping, but for serial production. AM offers a greater design freedom, compared to conventional production methods, which allows for parts with new innovative design. This is very attractive to the aerospace industry, in which parts could be designed to have reduced weight and improved performance contributing to reduced fuel consumption, increased payload and extended flight range. There are, however, challenges yet to solve before the potential of AM could be fully utilized in aerospace applications. One of the major challenges is how to deal with the poor fatigue behaviour of AM material with rough as-built surface. The aim of this thesis is to increase the knowledge of how AM can be used for high performance industrial parts by investigating the fatigue behaviour of the titanium alloy Ti6Al4V produced with different AM processes. Foremost, the intention is to improve the understanding of how rough as-built AM surfaces in combination with AM built geometrical notches affects the fatigue properties.This was done by performing constant amplitude fatigue testing to compare different combinations of AM material produced by Electron Beam Melting(EBM) and Laser Sintering (LS) with machined or rough as-built surfaces with or without geometrical notches and Hot Isostatic Pressing (HIP) treatment. Furthermore, the material response can be different between constant amplitude and variable amplitude fatigue loading due to effects of overloads and local plastic deformations. The results from constant amplitude testing were used to predict the fatigue life for variable amplitude loading by cumulative damage approach and these predictions were then verified by experimental variable amplitude testing. The constant amplitude fatigue strength of material with rough as-built surfaces was found to be 65-75 % lower, compared to conventional wrought bar, in which HIP treatments had neglectable influence on the fatigue strength. Furthermore, the fatigue life predictions with cumulative damage calculations showed good agreement with the experimental results which indicates that a cumulative damage approach can be used, at least for a tensile dominated load sequences, to predict the fatigue behaviour of additive manufactured Ti6Al4V.

Tese de doutoramento em Engenharia Mecânica, no ramo de Nanomateriais e Microfibras, apresentada ao Departamento de Engenharia Mecânica da Faculdade de Ciências e Tecnologia da Universidade de Coimbra
Reactive multilayers are desirable for a variety of applications including near-net shape shaping of intermetallic compounds, dissimilar/similar joining, as ignition sources and highly localized heat sources. The production of intermetallic compounds from multilayer thin foils/films is a widespread method. Due to its moderate enthalpy of reaction, the Ni-Ti system has received little attention in the context of low temperature joining; although the reaction product, nickel titanide, has promising mechanical properties, like superleasticity or shape memory effect. The aim of this PhD thesis is to study the feasibility of joining NiTi to Ti6Al4V using only the heat released by Ni/Ti reactive multilayers ignited, using a femtosecond laser. Ni/Ti reactive nano-multilayers with different modulation period (Λ =5 nm, 12 nm, 25 nm and 75 nm) and with a total thickness of around 2.5 µm were deposited, utilizing a dual cathode magnetron sputtering equipment, onto different substrates. These multilayer thin films exhibit a columnar growth, independently of the substrates, and a surface roughness that is directly proportional to the modulation period. Structural evolution was followed using in situ synchrotron x-ray diffraction, observing a single step reaction from Ni/Ti multilayers to B2-NiTi, without the formation of intermediate phases and independently of the substrate and modulation period. The temperature at which the multilayer structure evolves to the final phase varies with the period and the heating rate. When the multilayer thin film is deposited onto Ti6Al4V substrates, the nickel from the NiTi reacted multilayer, at temperatures higher than ≈650◦C, diffuse to the beta phase of the substrate leading to phase growth and NiTi2 formation. Ignition experiments were conducted on several of these multilayers using femtosecond laser pulses. It was observed that the substrates thermal properties plays a very important role: while metallic substrates quench the reaction confining it to the interacted laser volume, for zirconia substrates the reaction affected a wider volume. Based on a theoretical approach, it was confirmed that the produced multilayers did not present sufficient number of bilayers to be used as the only heat source available to promote joining. Concluding that, the number of bilayers had to be increased in order for the reaction to become self-sustained. LIPSS patterning of the multilayer revealed that the energy modulation irradiated on the multilayers surface promotes an athermal ablation on the bottom of the crests while, on the top, a small thickness of amorphous NiTi was observed. This indicates that, on the ridges, some of the multilayer reacted and that the process was not fully athermal. Finally, sound joints between NiTi and Ti6Al4V utilizing Ni/Ti multilayers with 12 and 25 nm periods were achieved at temperature as low as 600◦C for 30 min under a pressure of 10 MPa. The joints were processed, while following the phase evolution, using in situ synchrotron x-ray diffraction in transmission mode, revealing that the formation of the NiTi2 is reduced for the joints producedat lower temperatures. The joints presented good interface quality, without any pores or major defects.
As multicamadas reativas são interessantes para uma variedade de aplicações, incluindo a formação de componentes intermetálicos perto da forma final, soldadura similar e dissimilar, fonte de ignição e como fontes de calor altamente localizadas. A produção de compostos intermetálicos através de filmes finos/folhas, em multicamada, é um método generalizado. Devido à sua moderada entalpia de reação, o sistema Ni-Ti tem recebido pouca atenção, no contexto de ligações a temperaturas reduzidas, apesar do produto da reação (níquel titânio) ter propriedades mecânicas promissoras, como a superelasticidade ou efeito térmico de memória de forma. O objetivo desta tese de doutoramento é estudar a viabilidade de se ligar NiTi a Ti6Al4V, utilizando apenas o calor liberado pela reação das multicamadas de Ni/Ti quando acionadas por pulsos laser de femtosegundo. Foram depositadas nano-multicamadas reativas de Ni / Ti com diferentes períodos de modulação (Λ =5 nm, 12 nm, 25 nm and 75 nm), com uma espessura total de cerca de 2.5 µm, utilizando um equipamento de pulverização catódica por magnetrão (com dois cátodos) sobre substratos diferentes. Estes filmes finos de multicamada apresentam um crescimento colunar, independente- mente dos substratos, e uma rugosidade de superfície que é diretamente proporcional ao período de modulação. A evolução estrutural foi seguida usando difração de raios-x, através de radiação de sincrotrão in situ , observando-se que as multicamadas evoluíram de Ni/Ti para B2-NiTi num único passo, sem a formação de fases intermédias e independentemente do substrato e do período de modulação. A temperatura na qual a transição da estrutura das multicamadas evolui para a fase final varia de acordo com o período e a taxa de aquecimento. Quando os fimes finos multicamada são depositada sobre um substrato de TI6AI4V, o níquel do filme de NITi que reagiu da multicamada (a temperaturas superiores a ≈650 ◦C) vai difundir para a fase beta do substrato, conduzindo ao crescimento dessa fase e formação de NiTi2. Foram realizadas experiências de ignição em várias destas multicamadas, usando pulsos de laser de femtosegundo. Observou-se que as propriedades térmicas dos substratos desempenham um papel muito importante: enquanto os substratos metálicos extinguem a reação, confinando-a ao volume que o laser interage, para substratos de zircónia a reação afeta um volume mais amplo. Com base numa abordagem teórica, confirmou-se que as multicamadas produzidas não apresentam um número de bicamadas suficiente para serem usadas como a única fonte de calor disponível para promover a ligação. Partindo deste princípio, o número de bi-camadas tem que ser aumentado para que a reação se possa tornar auto-sustentável. Os padrões das LIPSS nas multicamadas revelaram que a modulação da energia irradiada na superfície promoveu uma ablação atérmica no fundo das cristas e, na parte superior, observou-se o desenvolvimento duma pequena espessura de NiTi amorfo. Isto indicia que existe reação nos topos das multicamadas e que o processo não foi totalmente atérmico.
FCT - SFRH/BD/68354/2010

Abstract Fiber Laser Welding (FLW) is a versatile joining technique of metals and alloys because it allows welding of dissimilar materials without filler material. FLW utilizes intensified heat energy to liquify the workpiece interface and joins when they are solidified. In this study, dissimilar joining between Ti6Al4V-Nitinol was performed using FLW process and the thermomechanical model was developed to understand the metallurgical mechanisms and investigate weldability of dissimilar alloys. The FLW of Ti6Al4V and Nitinol plates was performed with variable power density, welding speed, and focal distance. In this three-dimensional numerical model, heat flows in two different workpieces were computed during active laser welding and cooling process using a combined effect of radiation and convection. Both of the top and bottom surfaces of the welded zone were studied considering the combined effect from focused heat source and Argon shielding gas. Significant thermal cracks were produced through the welded interface. However, this numerical study illustrated thermomechanical foundation and discuss future challenges to improve the integrity and desirable FLW parameters in the dissimilar metal joining.

Abstract Finite element (FE) assisted numerical modeling approach is known as a popular approach to predict the machining performance of different machining operations. Tapping operation is a well-known manufacturing process that is used to cut threads efficiently. In the automotive and aerospace applications, precisely machined tapped holes are required in the small size deep holes. Tapping process creates thread in the hole and make it ready for fastening with other mating components. Tapping operation is considered as one of the most complex machining operations due to the presence of multi-flutes and multi-land involvement between the workpiece and cutter materials. The outcome of the tapping process results in the generation of threads and accepted as one of the most commonly employed in fastening methods for the joining of different machine components. Literature revealed that tapping process has been very rarely investigated using computational modeling approaches, as most of the available studies are experimental in nature. The experimental work for tapping operation can be very time and cost consuming because of the expensive fabrication of the cutting tools. It has also been observed experimentally that minor change in the threading profiles can generate significant difference in the cutting torque. A possible solution is to analyse the whole tapping operation using finite element (FE) assisted numerical simulation. Similarly, there will be limitation towards experiments if the workpiece material is expensive and difficult to cut. It is a common observation in metal cutting industry that most of the times cutting tap results in breakage when exposed to the higher magnitude of torque. The current study is aimed on the finite element based computational investigations on the tapping process using Ti6Al4V as a workpiece material. High hot hardness and low thermal conductivity of the Ti6Al4V also plays a significant role towards the poor machining performance of the threading tool. Ti6Al4V is most commonly employed in the engineering applications where high strength to weight ratio and ability of operate at higher temperatures is required. Ti6Al4V is mainly utilized in the automotive, aerospace, biomedical and petrochemical industries. It has been identified that tapping operation is very rarely studied machining operation in the metal cutting scientific community. Different tapping process conditions were investigated computationally using finite element (FE) approach and as a result cutting forces, torques and power consumed were observed. The study provides a useful understanding towards the tapping process mechanics with respect to different cutting parameters.