- Departamento de Engenharia Mecânica (Polo 2)
Rua Luis Rei Santos - 239790711
- I am a researcher in Material Science Engineering in Coimbra University, Portugaledit
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The present study aims to prepare feedstocks for MIM (Metal Injection Molding) where the metal powders are 316L stainless steel powders (SS). The master objective is to compare the performance of a biodegradable binder with a commercial... more
The present study aims to prepare feedstocks for MIM (Metal Injection Molding) where the metal powders are 316L stainless steel powders (SS). The master objective is to compare the performance of a biodegradable binder with a commercial one based on polyolefins. Different challenges must be overcome in SS injection molding, as follows: to decrease binder/carbon content in feedstocks; to decrease carbon contamination during debinding and sintering; to avoid the formation of chromium carbide and presence of precipitation-free zones; to avoid the grain growth during sintering and to reduce the feedstock price. The optimization of the feedstocks was performed using a torque rheometry technique. Feedstocks of coated and uncoated SS powders mixed with an agar-based binder were used to produce sound parts. A feedstock constituted by SS powders mixed with a high quality commercial binder was the standard. SS with agar-based on feedstocks can admit solids content similar to those based on th...
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ABSTRACT Micro hot embossing is a well-established technology to produce polymer microdevices and parts. This technology on metal powder/binder feedstocks is an innovator challenge that fits into the sustainable circular economy, being... more
ABSTRACT Micro hot embossing is a well-established technology to produce polymer microdevices and parts. This technology on metal powder/binder feedstocks is an innovator challenge that fits into the sustainable circular economy, being excellent for small series production of precision metallic parts. The powder hot embossing technology is integrated into processes denominated SDS (shaping, debinding, and sintering). This study presents the feasibility of replicating the die features into metallic parts by comparing two binders (Lc and M1). A new binder involves optimising critical parameters during hot embossing to ensure the replication of microdetails and the quality of metallic parts. Comparing the two binders, Lc contributes to the best precision of geometric details, and M1 improves surface quality. The study shows that hot powder embossing is a promising process to manufacture metallic parts with high precision and high-quality geometrical features on a microscale.
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TiAl-based intermetallic layers with additions of Ag, Cr, Y and Hf were deposited on γ-TiAl specimens using magnetron sputtering. The oxidation behaviour of the coated Ti-45Al-8Nb (at.%) alloy was investigated at 850 °C and 900 °C under... more
TiAl-based intermetallic layers with additions of Ag, Cr, Y and Hf were deposited on γ-TiAl specimens using magnetron sputtering. The oxidation behaviour of the coated Ti-45Al-8Nb (at.%) alloy was investigated at 850 °C and 900 °C under cyclic oxidation conditions in air. The ternary Ti-50Al-2Ag (at.%) coating did not provide oxidation protection to the substrate material at 850 °C. Two-phase γ-TiAl + Ti(Cr, Al)2 Laves coatings exhibited high oxidation resistance at 900 °C for up to 1000 cycles of 1 h dwell time at high temperature. During thermal exposure phase dissolution and transformation occurred. The slow oxide growth rates observed for the Ti – Al – Cr intermetallic layers were associated with the formation of a thin continuous alumina top scale established by the Laves, B2 and Z-phases. Small additions of hafnium and yttrium improved the oxidation resistance. In contrast, Ti – Al – Cr – Ag coatings exhibited poor oxidation behaviour at 900 °C.
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Reactive multilayer thin films that undergo highly exothermic reactions are attractive choices for applications in ignition, propulsion, and joining systems. Ni/Al reactive multilayer thin films were deposited by dc magnetron sputtering... more
Reactive multilayer thin films that undergo highly exothermic reactions are attractive choices for applications in ignition, propulsion, and joining systems. Ni/Al reactive multilayer thin films were deposited by dc magnetron sputtering with a period of 14 nm. The microstructure of the as-deposited and heat-treated Ni/Al multilayers was studied by transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) in plan view and in cross section. The cross-section samples for TEM and STEM were prepared by focused ion beam lift-out technique. TEM analysis indicates that the as-deposited samples were composed of Ni and Al. High-resolution TEM images reveal the presence of NiAl in small localized regions. Microstructural characterization shows that heat treating at 450 and 700°C transforms the Ni/Al multilayered structure into equiaxed NiAl fine grains.
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Metal powder hot embossing (MPHE) is a low-cost micromanufacturing technique that can produce metallic parts with aspects in micron scale. In this study, scanning electron microscopy (SEM) is employed for evaluating the shape retention... more
Metal powder hot embossing (MPHE) is a low-cost micromanufacturing technique that can produce metallic parts with aspects in micron scale. In this study, scanning electron microscopy (SEM) is employed for evaluating the shape retention and the homogeneity of microstructure of replicated geometries into AISI 316L powder feedstock by the secondary electron imaging (SEI) and the backscattered electron imaging modes, the distribution of chemical composition by the electron-dispersive spectroscopy (EDS) mapping, and grain structures by the electron backscatter diffraction technique. Moreover, the SEI and EDS techniques completed the failure analysis of tensile tests. Nanoindentations were also performed to assist phase identification analysis in the densified microstructure. Different geometries in the micron scale (micro wall half-reservoirs, micro channel half-flanges, convex and concave micro gear configurations, and micro tensile specimens) were selected for replication. Shaping limitations were attributed to the geometry, convex or concave, and the stiffness of the die. Micro gear and micro wall configurations were shaped using a stiffer elastomer (T = 230 °C and P = 11.3 to 14 MPa for 45 min) and a metallic die (T = 170 °C and P = 11.3 MPa for 10 min), respectively. The shaping of concave geometries was achieved regardless of the metal powder concentration, 60 and 65 vol.%. Densified parts retained the replicated micro configurations after long periods of thermal debinding and sintering, with densification above 95%. The chemical composition in sintered parts was homogeneous. The microstructure was principally composed of austenitic grains. The 316L stainless steel sintered part produced through MPHE presented an ultimate tensile strength of 458 ± 15 MPa, similar to that of a wrought AISI 316L alloy; the fracture type in the micro tensile specimen was ductile.
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The current research focuses on the shaping of aluminum feedstock by micro powder hot embossing. This method includes a mixture of powder with binder material for feedstock preparation. Then, shaping is accomplished by embossing,... more
The current research focuses on the shaping of aluminum feedstock by micro powder hot embossing. This method includes a mixture of powder with binder material for feedstock preparation. Then, shaping is accomplished by embossing, debinding and sintering. Micro powder hot embossing can be interested in the fabrication of parts when small series production is intended. The embossing step, to provide the designed configuration, is challenging and carried out using an elastomer die and uniaxial compaction. We evaluated the shaping process using aluminum feedstock and two geometries with similar aspect ratios (micro-channel half-flanges and micro-wall half-reservoirs). The micro-channel, half-flanges and half-reservoirs configurations were shaped using elastomer die; the micro-wall configuration was attained by the application of metallic die. For each die, the processing conditions (temperature, compaction and holding time) and shaping steps were selected to ensure the replicability and homogeneity of the green parts. The green parts were thermally debound and successfully sintered at a relatively high sintering temperature in a low-pressure atmosphere. The sintered parts retained their shapes and showed shrinkage.
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Ni/Al multilayers are known to transform into NiAl in a highly exothermic and self-sustaining reaction. The fact that this reaction has a high heat release rate and can be triggered by an external impulse, are reasons why it has already... more
Ni/Al multilayers are known to transform into NiAl in a highly exothermic and self-sustaining reaction. The fact that this reaction has a high heat release rate and can be triggered by an external impulse, are reasons why it has already attracted much research attention. There is a huge potential in the use of Ni/Al multilayers as a controllable and localized heat source for joining temperature-sensitive materials such as microelectronic components. The heat released and the phases resulting from the reaction of Ni and Al multilayers depend on the production methods, their composition, as well as the bilayer thickness and annealing conditions. The present research aims to explore the influence of these variables on the reaction of different multilayers, namely those produced by accumulative roll bonding (ARB) and sputtering. Structural evolution of Ni/Al multilayers with temperature was studied by differential scanning calorimetry, x-ray diffraction and scanning electron microscopy. Phase evolution, heat release rate and NiAl final grain size are controlled by the ignition method used to trigger the reaction of Ni and Al. The potential use of these multilayers in the diffusion bonding of TiAl was analyzed. The ARB multilayers allow the production of joints with higher strength than the joints produced with commercial multilayers (NanoFoil®) produced by sputtering. However, the formation of brittle intermetallic phases (Ni3Al, Ni2Al3 and NiAl3) compromises the mechanical properties of the joint.
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ABSTRACTTiAlN sputtered coatings have been used with success in high-speed cutting tools in the last few years. However, the adhesive failures of the coatings refrain its application in more severe wear conditions like as high-speed... more
ABSTRACTTiAlN sputtered coatings have been used with success in high-speed cutting tools in the last few years. However, the adhesive failures of the coatings refrain its application in more severe wear conditions like as high-speed machining. The assumptions for the present research were based on the hypothesis that thin metal interlayers will behave as shear stress sinkers, which could decrease the delamination of the thin films. In the present work, coatings of TiAlN with thin ductile metallic interlayers (Al, Ti, Cu and Ag) were deposited by reactive d.c. magnetron sputtering. Multilayer coatings with aluminum, titanium and silver interlayers achieve higher adhesion values (70N) than TiAlN monolithic coating (40N). Three and five metal ductile layers contribute to an increase of hardness and Young's modulus without change the residual stresses of the monolithic coating. Contrarily, the introduction of copper layers reduces all the studied mechanical properties of the TiAlN m...
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... 3030-788 Coimbra, Portugal sonia.simoes@fe.up.pt Keywords: nickel aluminides, multilayer, exothermic reaction Heating of thin multilayer systems can lead to stable or metastable phase formation. The structural evolution ...
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1 Departamento de Engenharia Metalúrgica e Materiais, GMM/IMAT, Faculdade de Engenharia, Universidade do Porto, Rua Dr. Roberto Frias, 4200465 Porto, Portugal 2 Departamento de Engenharia Mecânica, ICEMS, Universidade de Coimbra, Pólo... more
1 Departamento de Engenharia Metalúrgica e Materiais, GMM/IMAT, Faculdade de Engenharia, Universidade do Porto, Rua Dr. Roberto Frias, 4200465 Porto, Portugal 2 Departamento de Engenharia Mecânica, ICEMS, Universidade de Coimbra, Pólo II, Pinhal de Marrocos, ...
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The optimisation of joining technologies is essential to the application of advanced materials in the design of parts and devices. The development of intermetallic compounds, as structural materials, inevitably requires a new approach to... more
The optimisation of joining technologies is essential to the application of advanced materials in the design of parts and devices. The development of intermetallic compounds, as structural materials, inevitably requires a new approach to join these compounds to themselves or to other materials. Among different intermetallic classes, titanium aluminides are one of the most studied. However, the industrial application is far from being proportional to the research, due to different problems, where joining processes have an important role. The present paper highlights the state of art on joining γ-TiAl alloys. A review is presented with special emphasis on solid-state diffusion bonding process, because it seems to be the most suitable technique to produce high quality joints of advanced materials. The influence of the bonding conditions on the physical and mechanical properties of the joints is highlighted and the introduction of single or multiple interlayers to assist in the bonding ...
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Copper nitride films prepared by sputtering have applications such as optical data storage material, insulation barriers in micro electronic devices and coatings for mechanical applications. The present study examines nanocomposites... more
Copper nitride films prepared by sputtering have applications such as optical data storage material, insulation barriers in micro electronic devices and coatings for mechanical applications. The present study examines nanocomposites prepared by mechanical alloying of copper with copper nitride under nitrogen atmosphere, at room temperature, in order to establish a comparison with properties of Cu-N sputtered films. The powders were consolidated into bulk samples via warm extrusion at temperatures ranging from 300 to 500°C (0.42-0.64 Tf) after encapsulation without degassing. The as-milled powders and the extruded materials were studied using X-ray diffraction, optical microscopy, scanning and transmission electron microscopy and microhardness measurements. Also, the TEM observation of the extruded sample indicates a mean grain size of about 50 nm. This evidences a higher thermal stability of the as-milled powders and the advantage of using a fast consolidation process, at a relative...
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Extended abstract of a paper presented at Microscopy and Microanalysis 2007 in Ft. Lauderdale, Florida, USA, August 5 – August 9, 2007
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Research Interests: Materials Engineering, Materials Science, Scanning Electron Microscopy, Transmission Electron Microscopy, Scanning Transmission Electron Microscopy, and 11 moreIntermetallics, Differential scanning calorimetry, Thin Film, Nickel, Magnetron Sputtering, Phase Transformation, X ray diffraction, Room Temperature, Solid State, Solid State Reaction, and Film Thickness
... Eng. Sci. Proc. 14 (11-12) (1993), p.166. Tel: + 351 239 790 700, Fax: + 351 239 790 701, email: teresa.vieira@mail.dem.uc.pt 250 Advanced Materials Forum I Page 5. Advanced Materials Forum I doi:10.4028/www.scientific.net/KEM.230-232... more
... Eng. Sci. Proc. 14 (11-12) (1993), p.166. Tel: + 351 239 790 700, Fax: + 351 239 790 701, email: teresa.vieira@mail.dem.uc.pt 250 Advanced Materials Forum I Page 5. Advanced Materials Forum I doi:10.4028/www.scientific.net/KEM.230-232 ...
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The diffusion bonding of Ti-6Al-4V to NiTi alloys assisted by Ni/Ti reactive multilayer thin films indicates the diffusion of Ni from the filler material towards bulk Ti-6Al-4V. As a consequence, the fragile NiTi2 intermetallic phase is... more
The diffusion bonding of Ti-6Al-4V to NiTi alloys assisted by Ni/Ti reactive multilayer thin films indicates the diffusion of Ni from the filler material towards bulk Ti-6Al-4V. As a consequence, the fragile NiTi2 intermetallic phase is formed at the joint interface. In this context, the aim of this work is to investigate the occurrence of Ni diffusion from Ni/Ti nanomultilayers towards Ti-6Al-4V substrates. For this purpose, multilayer coated Ti alloys were studied in situ at increasing temperatures using synchrotron radiation. After heat treatment, scanning electron microscopy (SEM) analyses were carried out and elemental map distributions were acquired by electron probe microanalysis (EPMA). The EPMA maps confirm the occurrence of Ni diffusion; the presence of Ni in the substrate regions immediately underneath the nanomultilayers is clearly indicated and becomes more pronounced as the temperature increases. The presence of Ni is observed in the same locations where V is found, th...
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Additive manufacturing (AM) is one of the most trending technologies nowadays, and it has the potential to become one of the most disruptive technologies for manufacturing. Academia and industry pay attention to AM because it enables a... more
Additive manufacturing (AM) is one of the most trending technologies nowadays, and it has the potential to become one of the most disruptive technologies for manufacturing. Academia and industry pay attention to AM because it enables a wide range of new possibilities for design freedom, complex parts production, components, mass personalization, and process improvement. The material extrusion (ME) AM technology for metallic materials is becoming relevant and equivalent to other AM techniques, like laser powder bed fusion. Although ME cannot overpass some limitations, compared with other AM technologies, it enables smaller overall costs and initial investment, more straightforward equipment parametrization, and production flexibility.This study aims to evaluate components produced by ME, or Fused Filament Fabrication (FFF), with different materials: Inconel 625, H13 SAE, and 17-4PH. The microstructure and mechanical characteristics of manufactured parts were evaluated, confirming the...
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The strengthening effect on aluminium (Al) by ultrafine particles of tungsten carbide (WC) after compacting and sintering was evaluated. The Al-1 vol.% WC mixture was prepared through a high-speed stirring technique, called assisted... more
The strengthening effect on aluminium (Al) by ultrafine particles of tungsten carbide (WC) after compacting and sintering was evaluated. The Al-1 vol.% WC mixture was prepared through a high-speed stirring technique, called assisted sonication. In this study, the effects of compacting, sintering temperature and holding time were evaluated by composite microstructural characterization and by mechanical tests. The characterizations involved electron dispersive spectroscopy and X-ray diffraction techniques for phase identification; electron backscattered diffraction for crystallographic analysis; backscattered electrons and secondary electrons imaging for failure and wear studies. In all composites, hardness was determined; for the hardest composite, the tensile strength, flexural strength and ball scattering wear resistance were also evaluated. The Al-1 vol.% WC composite produced by assisted sonication, densified by cold compacting at 152 MPa and sintered at 640 °C for 2 h at 5 × 10−...
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Hot embossing is a small-scale, low-cost processing technology that can deliver products to the market in a short time. This microreplication technology is well established to produce polymeric components and has applications in several... more
Hot embossing is a small-scale, low-cost processing technology that can deliver products to the market in a short time. This microreplication technology is well established to produce polymeric components and has applications in several industrial sectors. The use of micropowder hot embossing in the production of metal components is an emerging and challenging process that, when compared to other typical technologies, brings some economic advantages in a volatile market with an increasing tendency to manufacture customized products. The main objective of this review is to analyze the potential of powder hot embossing and its developments in the production of metallic microparts/components. This technology requires four distinct steps: (1) production feedstock (preparation of mixtures), (2) hot embossing (shape forming), (3) debinding and (4) sintering. These steps are interrelated and influence the characteristics of the final metallic microparts. This study summarizes the approache...
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In metal powder, shaping the preparation and characterization of the feedstock is an aspect commonly recognized as fundamental. An optimized composition is required to ensure the successful shaping of the feedstock. In this study, a... more
In metal powder, shaping the preparation and characterization of the feedstock is an aspect commonly recognized as fundamental. An optimized composition is required to ensure the successful shaping of the feedstock. In this study, a commercial binder system, pure aluminum and 316L austenitic stainless-steel powders were used for micro hot embossing. The optimization process revealed that powder characteristics such as shape and the stability of the torque mixing, were important parameters. Manipulating the feedstock composition by adding multi-walled carbon nanotubes or stearic acid or using a higher powder concentration considerably influenced the torque mixing values. The steady state of torque mixing was achieved for all feedstocks. This torque behavior indicates a homogeneous feedstock, which was also confirmed by microscopic observations. Nevertheless, an extruding process was required for greater homogeneity of the aluminum feedstocks. The presence of the carbon nanotubes incr...
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Challenge tests for food-dependent exercise-induced anaphylaxis (FDEIA) carry some risk and have a high rate of false negatives. Our aim was to explore the usefulness of an in vitro immunodepletion assay and an allergen microarray test in... more
Challenge tests for food-dependent exercise-induced anaphylaxis (FDEIA) carry some risk and have a high rate of false negatives. Our aim was to explore the usefulness of an in vitro immunodepletion assay and an allergen microarray test in the identification of IgE-mediated cross-reactive food allergens in patients with suspected FDEIA or food-dependent exercise-induced urticaria and panallergen sensitization. Three patients with a history of food dependent exercise induced urticaria/anaphylaxis and food panallergen sensitization in whom a food-exercise challenge was not feasible were selected: a 25-year-old man with cholinergic urticaria who experienced generalized urticaria and angioedema during a soccer match after drinking a peach-based soft drink; a 19-year-old woman with allergic rhinitis and controlled asthma who experienced anaphylactic shock while playing soccer, having eaten walnuts in the previous 90 min; and a 57-year-old man with baker's asthma who experienced four e...
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The microfabrication technologies not only possess a considerable market potential but are also regarded as leading technologies of our days and key technologies for the future, due to the growing demand for microengineering applications... more
The microfabrication technologies not only possess a considerable market potential but are also regarded as leading technologies of our days and key technologies for the future, due to the growing demand for microengineering applications such as micromoulds, micromechanical structures, sensors and micro-medical devices [1,2]. Metal powder hot embossing is an emerging replicative process that can provide dimensional precision and microdetails of metallic parts. Metal powder hot embossing requires four distinctive steps: (1) preparation of feedstocks (implying the selection and characterization of powder and binder); (2) shape-forming of the part by hot embossing (green part); (3) debinding (brown part); and (4) sintering (final part).
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Citation & Copyright (to be inserted by the publisher ) ... Study of Sintering Variables of Tungsten Carbide Particles Sputter-Deposited with Stainless Steel ... CM Fernandes 1 , AMR Senos 1,* and MT Vieira 2 ... 1 Department of... more
Citation & Copyright (to be inserted by the publisher ) ... Study of Sintering Variables of Tungsten Carbide Particles Sputter-Deposited with Stainless Steel ... CM Fernandes 1 , AMR Senos 1,* and MT Vieira 2 ... 1 Department of Ceramics and Glass Engineering, CICECO, ...
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In the present work, thin films of hydroxyapatite (HAp), titanium, and hydroxyapatite doped with different titanium concentrations were obtained by sputtering and characterized using several analytical techniques. These films are intended... more
In the present work, thin films of hydroxyapatite (HAp), titanium, and hydroxyapatite doped with different titanium concentrations were obtained by sputtering and characterized using several analytical techniques. These films are intended to be used as model surfaces on protein adsorption studies in order to better understand the role of titanium ions in biological processes.
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Nanocrystalline metals demonstrate a broad range of fascinating mechanical properties at the nanoscale, namely a significant increase in hardness and superior yield stress. In this regard, understanding grain growth in nanocrystalline... more
Nanocrystalline metals demonstrate a broad range of fascinating mechanical properties at the nanoscale, namely a significant increase in hardness and superior yield stress. In this regard, understanding grain growth in nanocrystalline metals is crucial, particularly because nano size grains are characterized by a high curvature, which results in a high driving force for grain growth. In this work, the effect of annealing conditions on grain size of copper nanocrystalline thin films was investigated. The nanocrystalline copper thin films were first deposited by d.c. magnetron sputtering on a copper substrate. The specimens were then annealed in vacuum at 100, 300 and 500°C from 10 minutes to 5 hours. Transmission electron microscopy observations revealed that the as-deposited thin films have a bimodal grain size distribution; an average grain size of 43±2nm and the presence of nanotwins. Abnormal grain growth was observed for some samples annealed. Increasing the annealing time induc...
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The aim of this work is to join -TiAl intermetallics to Ni based superalloys by solid state diffusion bonding. The surface of the -TiAl alloys and Ni superalloys to be joined was prepared by magnetron sputtering with a few microns thick... more
The aim of this work is to join -TiAl intermetallics to Ni based superalloys by solid state diffusion bonding. The surface of the -TiAl alloys and Ni superalloys to be joined was prepared by magnetron sputtering with a few microns thick Ni/Al reactive multilayer thin films with nanometric modulation periods. Sound joining without cracks or pores is achieved along the central region of the bond, especially at 800°C and when a 14 nm period Ni/Al film is used as filler material. During the diffusion bonding experiments interdiffusion and reaction inside the Ni/Al multilayer thin film and between the interlayer film and the base materials is promoted with the formation of intermetallic phases. The final reaction product in the multilayer films is the B2-NiAl intermetallic phase. The interfacial diffusion layers between the base materials and the multilayer films should correspond to: 3-NiTiAl and 4-Ni2TiAl phases from the -TiAl side; Ni-rich aluminide and -phase from the Inconel s...
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Page 1. Citation & Copyright (to be inserted by the publisher ) Corresponding author: manuela.oliveira@ineti.pt Manufacture of Ceramic Products Using Inertized Aluminum Sludges IMMartins 1 , S.Vieira 2 , V. Livramento 1 ,... more
Page 1. Citation & Copyright (to be inserted by the publisher ) Corresponding author: manuela.oliveira@ineti.pt Manufacture of Ceramic Products Using Inertized Aluminum Sludges IMMartins 1 , S.Vieira 2 , V. Livramento 1 , J. Sousa 1 , F. Delmas 1 , ...
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Diffusion bonding of TiAl alloys can be enhanced by the use of reactive nanolayer thin films as interlayers. Using these interlayers, it is possible to reduce the conventional bonding conditions (temperature, time, and pressure) and... more
Diffusion bonding of TiAl alloys can be enhanced by the use of reactive nanolayer thin films as interlayers. Using these interlayers, it is possible to reduce the conventional bonding conditions (temperature, time, and pressure) and obtain sound and reliable joints. The microstructural characterization of the diffusion bond interfaces is a fundamental step toward understanding and identifying the bonding mechanisms and relating them to the strength of the joints. The interface of TiAl samples joined using Ni/Al nanolayers was characterized by transmission electron microscopy and scanning transmission electron microscopy. Microstructural characterization of the bond revealed that the interfaces consist of several thin layers of different composition and grain size (nanometric and micrometric). The bonding temperature (800, 900, or 1,000°C) determines the grain size and thickness of the layers present at the interface. Phase identification by high-resolution transmission electron micr...
Research Interests: Materials Engineering, Condensed Matter Physics, Materials Science, Electron Microscopy, Transmission Electron Microscopy, and 9 moreScanning Transmission Electron Microscopy, Medicine, High Resolution Transmission Electron Microscopy, Grain Boundary, Diffusion bonding, Intermetallic Compounds, Energy Dispersive X Ray Spectroscopy, Electron Energy Loss Spectroscopy, and Biochemistry and cell biology
Research Interests: Materials Engineering, Condensed Matter Physics, Materials Science, Heat Treatment, Mechanical properties, and 9 moreThin Film, Grain size, Surface and Coatings Technology, Phase Transformation, Room Temperature, Intermetallic Compounds, Titanium Aluminides, Ultimate Tensile Strength, and Mechanical Property
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Materials mechanical resistance is known to depend on the size of structural features, accordingly to the familiar HallPetch equation. For the nanometer range of grain sizes, this relationship breaks down and a change of the grain size... more
Materials mechanical resistance is known to depend on the size of structural features, accordingly to the familiar HallPetch equation. For the nanometer range of grain sizes, this relationship breaks down and a change of the grain size exponent is needed to satisfy this dependency. Nevertheless, the superior strength of the nanocrystalline material relays on the small dimension of its grains. Characterization of the thermal stability of these materials becomes relevant since a large fraction of atoms are in the grain boundaries and, as a result, its structure posses a large excess of energy that promotes grain growth. Grain growth in nanocrystalline metals has been observed well below the temperatures needed to promote grain growth in coarse grained materials; in some cases, even at room temperature. From this perspective, the study of grain growth in nanocrystalline metals is crucial for the development of new nanocrystalline materials with outstanding mechanical properties. There ...
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Research Interests: Materials Engineering, Mechanical Engineering, Materials Science, Finite Element, Thin Films, and 13 moreNumerical Simulation, Thin Film, Optical microscopy, Ductility, Composite Material, Three Dimensional, Experimental Tests, Tensile testing, Thin film deposition, Stress (Linguistics), Tensile Test, Ultimate Tensile Strength, and cross sectional area
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ABSTRACT a b s t r a c t Solid state diffusion bonding has been successfully employed to join -TiAl alloys. Processed in vacuum, at high temperature and pressure, the thin interfaces and the lack of structural discontinuity across the... more
ABSTRACT a b s t r a c t Solid state diffusion bonding has been successfully employed to join -TiAl alloys. Processed in vacuum, at high temperature and pressure, the thin interfaces and the lack of structural discontinuity across the interface are the main advantage of this joining technique. An interlayer made of alternated Ti and Al nanometric layers that increases the diffusivity at the joint interface, was used in order to assist the bond-ing process of -TiAl alloys. The use of Ti/Al interlayer has efficiently reduced the joining temperature. Sound joints have been achieved at a temperature of 900 • C under a pressure of 50 MPa in vacuum. In the present work Cu was added as third element to the Ti/Al multilayers and its effect improved the bonding quality. The interface microstructure was studied by scanning and transmission electron microscopy.