Soft magnetic materials have been widely used in electric motors, routers, and detectors. Tremendous studies have been conducted to report microstructural features corresponding to magnetic performance. The laser-based powder bed fusion (L-PBF) additive manufacturing technique was implemented to bulk-scale fabricate the Finemet nanocrystalline magnetic alloy. This research study aims to reveal the capability of replacing the traditional melt spinning process with decent bulk density and magnetic properties. Nanocrystalline materials originate from optimizing amorphous metallic alloys, resulting in low coercivity and high saturation magnetization by facilitating the formation of nanocrystals. An extremely high cooling rate is the foundational factor for controlling the microstructure. Selective Laser Melting (SLM) offers a layer thickness of 20-100 µm, naturally providing a cooling rate of 105 - 107 K/s. Subsequent melting will impact the microstructure by conducting heat continuously through the melt pools. The relationship between microstructural features and crystalline phase characterization is discussed. Magnetic characterization, in terms of saturation magnetization and coercivity, with various processing parameters, is investigated. / Master of Science / Additive manufacturing of Finemet soft magnetic materials to approach expected microstructure and magnetic properties open up the path of replacing traditional manufacturing techniques. Freedom of complicated near net morphology design and inter-layer microstructural control by manipulating processing parameters offer revolutionary fabrication process comparing to traditional casting and welding. The magnetic performance of soft magnetic materials in real life applications such as electric motor is depending on multiple factors. Thus, the fascinating magnetic properties of soft magnetic materials owing strict requirement of microstructure and crystallite size. Aside from magnetic properties, as-printed bulk density fabricated by SLM would hugely impact the overall mechanical properties and porosity. Thus, processing parameters optimization through experiment and characterization would significantly benefit this study. Afterwards, comparison groups of samples with decent bulk density were taken into characterizations to reveal the crystalline phases, microstructure of metallic phases with respect to the melt pool morphology and then magnetic property of coercivity and saturation magnetization were carefully analyzed.

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La machine synchrone à griffes est un dispositif très utilisé comme alternateur dans l’automobile. La fabrication de cette machine, produite en masse, met en œuvre des procédés impactant les caractéristiques des matériaux ferromagnétiques et donc, in fine , les performances de l’alternateur. Ce travail de thèse est donc consacré à étudier l’impact du processus de fabrication d’un stator Slinky (basé sur un enroulement d’une bande de tôle plutôt qu’un empilement) sur les propriétés magnétiques. Pour ce faire, une première partie du travail consiste à quantifier l’impact de chaque procédé mis en œuvre. Le but est de séparer les procédés les plus fortement impactant. Une campagne de caractérisation magnétique, sur des échantillons prélevés avant et après chaque procédé, a été réalisée. Les résultats montrent que le procédé d’enroulement est l’étape la plus destructive à cause des déformations et des contraintes engendrées dans le plan de la tôle à la fois en traction et en compression. L’optimisation de ce procédé nécessite donc d’établir le lien entre les propriétés mécaniques et magnétiques. Nous proposons une nouvelle méthode de caractérisation magnéto-mécanique. Elle permet de réaliser une caractérisation magnétique sous chargement uni axial en traction et en compression. Enfin, nous présentons des résultats montrant l’évolution du comportement magnétique, d’un matériau FeSi NO, en fonction de la déformation et de la contrainte appliquée. / The synchronous claw pole machine represents a widely used device, as an alternator, in the automobile industry. The production of this machine implements a line of several processes which impact the characteristics of ferromagnetic materials and, ultimately, the performance of the alternator. Therefore, this work is devoted to studying the impact of the manufacturing processes of a Slinky stator (based on a rolled sheet metal strip rather than stacked sheets) on the magnetic properties. To reach our goal, a first task consists in quantifying the impact of each manufacturing process. The aim is to separate the most detrimental processes. Thus, a magnetic measurement campaign was carried out on samples withdrawn before and after each process.The results show that the rolling step represents the most detrimental process due to the generated stresses and strains in the plane of the sheet in both modes (tension and compression). Therefore, the optimization of this process requires setting up the link between the mechanical and magnetic properties. Hence, we propose a new method of magneto-mechanical characterization. It enables to carry out magnetic measurements under uniaxial loading (tension and compression). Finally, we present results showing the evolution of the magnetic behavior of a FeSi NO material depending on the applied stress and strain.

Fe-based amorphous powders are fabricated through gas and water atomization using industrial grade raw materials. The atomic structure of the powder is examined by X-Ray Diffraction (XRD). Eight of totally thirteen different compositions are proved completely amorphous or amorphous with traces of crystalline phase in the desired powder particle size (d > 75 μm) and five are crystalline. It reveals that the Glass Forming Ability (GFA) of atomized powders is well correlated to the GFA of as-casted rods or melt-span ribbons. In the present study at least 1.5-2 mm critical size of GFA for a target composition is necessary for the formation of amorphous powders in the desired particle size. The thermal stability of the amorphous powder is examined by Differential Scanning Calorimetry (DSC). Applying the conventional powder metallurgy process the amorphous powders are mixed with the crystalline Somaloy® 110i, a commercial Soft Magnetic Composite (SMC) material from Höganäs AB in Sweden, and made into toroid-shaped components. The components are annealed aiming for improved soft-magnetic properties. The magnetic measurements are taken on copper-wire double coiled toroids. As a result, the total magnetic flux (B), coercivity (HC) and permeability (μmax) is reduced due to the addition of amorphous powders to Somaloy® 110i powder but the core losses (P) is at the same level despite reduced density. An improved soft magnetic property and core loss is revealed by the comparison to recent literature reports on SMC mixing of crystalline and amorphous powders.

<p>Microrobots have a promising prospect to be used in healthcare and bioengineering applications due to their capability to gently access small and delicate body sites. Unfortunately, traditional materials used for the fabrication of microrobots are rigid, hindering safe operation due to the transfer of high stresses to the surrounding tissue. Additionally, traditional microrobots are often not biocompatible, which threatens the health of the patient if not properly retrieved. This dissertation describes the fabrication and actuation of small-scale (several micrometers in all dimensions) magnetic robots that are soft, biocompatible, and capable of moving over smooth and corrugated surface. <u>S</u>oft <u>M</u>agnetic <u>M</u>icro <u>R</u>obots (SMµRs) can carry payloads in their porous interior and release them using external magnetic inputs. SMµRs has therefore the potential to be used in a wide range of applications—including targeted drug release and remote biosensing and bio sampling—and access a number of difficult-to-reach sites in the human body, such as intestines or blood vessels. The structure of SMµRs consist of three thin layers: Two layers of polymer with embedded magnetic particles aligned along a preferential direction. One porous layer, in between the magnetic layers, where the SMµRs can accumulate and release payloads. SMµRs are small, light in weight, and fast and inexpensive to fabricate. Moreover, the manufacturing of SMµRs is compatible with large-scale production processes, facilitating their future commercial exploitation. Using external rotating magnetic fields, the position of the SMµRs can be controlled wirelessly <i>via</i> tumbling locomotion. We demonstrate two types of tumbling locomotion (length-wise and side-wise) as well as the possibility to release the internal payload of the SMµRs in a discrete or continuous manner using only changes in the intensity of the external magnetic field. We studied the performance of SMµRs under a variety of environmental conditions as well as their capability of overcoming obstacles.</p>

In this study, prealloyed austenitic stainless steel and premixed soft magnetic Ni-Fe permalloy compacts were consolidated through microwave and conventional sintering routes at combinations of various sintering temperatures and compaction pressures. Sintered alloys were characterized in terms of their densification, microstructural evolution as well as mechanical and magnetic properties. The effect of sintering method in terms of the applied sintering parameters on the final properties of the compacts were investigated in a comparative manner. It was determined that microwave sintered permalloys are superior compared to their conventionally sintered counterparts in densification response, microstructural characteristics such as pore shape and distribution as well as mechanical properties for both austenitic stainless steel and permalloy compacts. However, permeability of the microwave sintered permalloys was inferior to their conventionally sintered counterparts in some cases due to microstructural refinement associated with microwave sintering route.

Este trabalho tem como objetivo o projeto, construção e análise do funcionamento de uma máquina elétrica síncrona trifásica com núcleo do rotor produzido a partir da metalurgia do pó e ímãs de neodímio-ferro-boro para aplicação em aerogeradores. Tomando como base a máquina elétrica modelo VTOP da fabricante Grupo Voges, foram realizadas mudanças na forma construtiva dos núcleos do estator e do rotor. O pacote chapas que compõem o núcleo do estator foi montado de maneira que as ranhuras apresentem um ângulo de inclinação de 10º ao longo de toda a extensão da máquina. Para o rotor, foi projetado e construído um núcleo através do processo de metalurgia do pó utilizando como matéria-prima pó de ferro puro. A esse novo núcleo foram acrescentados ímãs de neodímio-ferro-boro. Após a montagem dos componentes, a máquina elétrica foi ensaiada em uma bancada de testes. Paralelamente com a confecção do núcleo foi efetuada a simulação computacional da máquina com três tipos diferentes materiais no núcleo do rotor. Os resultados encontrados indicaram que a metalurgia do pó é uma alternativa viável para produção do núcleo de máquinas elétricas. Entretanto alterações na topologia e na forma de fixação dos ímãs são necessárias para um melhor desempenho. / This work aims at the design, construction and performance analysis of a three-phase synchronous electric machine with a rotor core produced by powder metallurgy and neodymium-iron-boron magnets for application in wind turbines. Based on the electric machine VTOP model of the manufacturer Grupo Voges, changes were carried out in the constructive form of the stator and rotor cores. The bundle of plates that make the role of stator core were mounted with a 10º slope along the entire length of the machine. For the rotor, a core was designed and built by employing powder metallurgy process using pure iron powder as raw material. The neodymium-iron-boron magnets were added to this new core. After assembling the components, the electric machine was tested on a test bench. Simultaneously with the core fabrication, the machine was simulated with three different materials in the rotor core. The results indicated that powder metallurgy is a viable alternative to produce the core of electric machines. However, changes in the topology and shape of the magnets are necessary for better assembly, improving the performance.

Este trabalho tem como objetivo o projeto, construção e análise do funcionamento de uma máquina elétrica síncrona trifásica com núcleo do rotor produzido a partir da metalurgia do pó e ímãs de neodímio-ferro-boro para aplicação em aerogeradores. Tomando como base a máquina elétrica modelo VTOP da fabricante Grupo Voges, foram realizadas mudanças na forma construtiva dos núcleos do estator e do rotor. O pacote chapas que compõem o núcleo do estator foi montado de maneira que as ranhuras apresentem um ângulo de inclinação de 10º ao longo de toda a extensão da máquina. Para o rotor, foi projetado e construído um núcleo através do processo de metalurgia do pó utilizando como matéria-prima pó de ferro puro. A esse novo núcleo foram acrescentados ímãs de neodímio-ferro-boro. Após a montagem dos componentes, a máquina elétrica foi ensaiada em uma bancada de testes. Paralelamente com a confecção do núcleo foi efetuada a simulação computacional da máquina com três tipos diferentes materiais no núcleo do rotor. Os resultados encontrados indicaram que a metalurgia do pó é uma alternativa viável para produção do núcleo de máquinas elétricas. Entretanto alterações na topologia e na forma de fixação dos ímãs são necessárias para um melhor desempenho. / This work aims at the design, construction and performance analysis of a three-phase synchronous electric machine with a rotor core produced by powder metallurgy and neodymium-iron-boron magnets for application in wind turbines. Based on the electric machine VTOP model of the manufacturer Grupo Voges, changes were carried out in the constructive form of the stator and rotor cores. The bundle of plates that make the role of stator core were mounted with a 10º slope along the entire length of the machine. For the rotor, a core was designed and built by employing powder metallurgy process using pure iron powder as raw material. The neodymium-iron-boron magnets were added to this new core. After assembling the components, the electric machine was tested on a test bench. Simultaneously with the core fabrication, the machine was simulated with three different materials in the rotor core. The results indicated that powder metallurgy is a viable alternative to produce the core of electric machines. However, changes in the topology and shape of the magnets are necessary for better assembly, improving the performance.

Les alliages Fe-Si sont connus pour combiner d’excellentes propriétés magnétiques avec de bonnes propriétés électriques (forte résistivité électrique). Dans ce contexte nous avons recherché à élaborer des matériaux à forte teneur en Si, souvent difficiles à obtenir et mettre en forme industriellement. Des alliages magnétiques doux de type Fe-Si avec une teneur élevée en Si (4,5%, 6,5%, 10% et 15% massique) ont été obtenus avec succès à l’état nanocristallin par broyage mécanique et recuit. La formation des alliages a été étudiée par diffraction X, spectroscopie Mössbauer et analyses thermomagnétiques. La stabilité thermique de la poudre a été analysée par DSC. Des mesures d’aimantation ont été réalisées pour caractériser les performances magnétiques. La durée de broyage nécessaire pour la formation de l’alliage a été déterminée pour chaque teneur en Si. Pour les faibles temps de broyage, le recuit conduit à la formation du composé Fe3Si. Après la formation de l’alliage par le broyage mécanique, l’effet du recuit est seulement de réduire les tensions internes du second ordre, induites dans la poudre par le broyage. L’addition de Si conduit à la diminution de la température de Curie de 770 °C pour le Fe pur, à 725 °C pour une teneur de 4,5% massique de Si et à 550 °C pour 15% massique de Si. Pour les temps faibles de broyage, l’écart entre l’aimantation de la poudre avant et après recuit est dû à la formation du composé Fe3Si pendant le recuit, lequel a une aimantation plus faible que la solution solide de Feα(Si). Pour les longs temps de broyage, le recuit à 400 °C pour 4 heures n’a pas d’effet sur la valeur de l’aimantation à saturation. En augmentant la teneur en Si, l’aimantation à saturation de l’alliage Fe-Si décroit.Les alliages Ni3Fe (aussi connus comme Permalloys) présentent de meilleures propriétés magnétiques, mais ils ont une résistivité inférieure à celles des Fe-Si. Une voie attractive semble la combinaison des propriétés des 2 classes de matériaux doux en formant un composite. Les alliages Fe-Si précédemment obtenus ont été utilisés pour l’élaboration des poudres composites de type Permalloy/Fe-Si par la mécanosynthèse. Le broyage mécanique conduit à la formation des particules composites avec un aspect stratifié. Quatre heures de broyage de l’alliage Fe-Si avec du Ni3Fe ne conduisent pas à la formation des nouvelles phases, mais la formation d’un alliage ternaire Ni-Fe-Si résulte d’un recuit ultérieur à 900 °C. L’aimantation à saturation du composite augmente avec la croissance de la teneur le d’alliage Fe-Si, mais le temps de broyage ne semble avoir aucun effet sur cela.Une étude préliminaire a été réalisée sur l’élaboration des compacts composites de type Ni3Fe/Fe-Si par frittage flash, dans le but de préserver l’état nanocristallin par de basses températures de frittage. L’influence de la température de frittage et de la durée de maintien sur la structure, et les propriétés physiques des compacts est discutée. Des températures allant jusqu'à 750 °C pour une durée de maintien minimale ou un palier de 2 minutes maximum à 700 °C ne conduisent pas à la diffusion des éléments des alliages. L'augmentation de la température ou de la durée de frittage conduit à des cristallites plus grandes, mais qui restent dans le domaine nano pour les températures étudiées. La densité des compactes augmente avec la température et le palier. En outre, la résistivité diminue en augmentant ces 2 paramètres. L'effet de la teneur en Fe-Si est de diminuer la densité et en même temps d'augmenter la résistivité des compacts. La perméabilité magnétique est réduite avec l'augmentation de la température et de la durée de frittage, ainsi que lors de la diminution du contenu de Ni3Fe. Une température élevée et un long temps de maintien à la température de frittage conduisent à l’augmentation des pertes magnétiques. Le champ coercitif est également influencé par les paramètres de frittage, via l'effet qu'ils ont sur la taille des cristallites. / Fe-Si alloys are known for combining excellent magnetic properties with good electric characteristics (high resistivity). In this context we sought to develop materials with a relatively high Si content, often difficult to obtain and shape industrially.In this thesis, soft magnetic Fe-Si alloys with high Si content (4.5, 6.5, 10 and 15 wt. %) were successfully obtained in nanocrystalline state by mechanical alloying and annealing. The formation of the alloy was studied by X-ray and neutron diffraction, Mossbauer spectroscopy and thermomagnetic analysis. DSC technique was used in order to study the powder’s thermal stability. Magnetisation measurements were also made in order to characterise their magnetic performances. The milling duration necessary for the formation of the alloy was determined for each Si content. For low milling times, annealing leads to the formation of the Fe3Si compound. Once the alloy is formed by mechanical milling, the effect of the annealing is only to reduce the second order stress induced in the powder by the milling process. Si addition leads to the decrease of the alloy’s Curie temperature from 770 °C for pure Fe to 725 °C for a 4.5 wt. % Si and down to 550 °C if the Si content increases to 15 wt. %. For low milling times, a gap between the magnetisation of the as-milled alloy and of the milled and subsequently annealed one is due to the formation of the Fe3Si compound during annealing which has a lower magnetisation than that of the αFe (Si) solid solution. For longer milling durations, annealing at 400 °C for 4 hours has no effect on the saturation magnetisation value. By increasing the Si content, the Fe-Si alloy’s saturation magnetisation decreases.Fe-Ni alloys whose composition is close to Ni3Fe (commonly known as Permalloys) have better magnetic properties, but a resistivity well inferior to that of Fe-Si alloys. Therefore, a combination of the properties of these 2 alloy classes of soft magnetic materials into a composite seems to be an attractive route. The previously obtained Fe-Si alloys were used for the preparation of Permalloy/Fe-Si composite powders by mechanical milling. Milling leads to the formation of composite powder particles with a stratified aspect. Milling of the Fe-Si and Ni3Fe alloys for 4 hours does not lead to the formation of new phases, but a subsequent annealing at 900 °C results in the formation of a Ni-Fe-Si alloy. Saturation magnetisation of the composite increases with increasing of the Fe-Si content, but milling duration seems to have no effect on it.A preliminary study was made on the elaboration of Ni3Fe/Fe-Si composite compacts obtained by spark plasma sintering, aiming to preserve the nanocrystalline state by lower sintering temperatures. The influence of the sintering temperature and temperature holding duration on the structure, density, resistivity and magnetic properties of the compacts is discussed. Temperatures of up to 750 °C for minimal holding duration or a maintain at the temperature of 700 °C for a duration of up to 2 minutes does not lead to a diffusion of the alloys’ elements. Increasing of the sintering temperature or duration leads to larger crystallite sizes, but they remain in the nano domain for the studied temperatures. The compacts’ density increases with temperature and sintering duration. Resistivity, on the other hand decreases when increasing the aforementioned parameters. The effect of the Fe-Si content is to decrease the density and at the same time increase the compacts’ resistivity. Magnetic permeability is reduced with increasing sintering temperature and duration, as well as when decreasing of the Ni3Fe content. High temperature and long maintaining duration leads to an increase of magnetic losses. Coercive field is also influenced by sintering parameters by the effect they have on the crystallite size.

Este trabalho tem como objetivo o projeto, construção e análise do funcionamento de uma máquina elétrica síncrona trifásica com núcleo do rotor produzido a partir da metalurgia do pó e ímãs de neodímio-ferro-boro para aplicação em aerogeradores. Tomando como base a máquina elétrica modelo VTOP da fabricante Grupo Voges, foram realizadas mudanças na forma construtiva dos núcleos do estator e do rotor. O pacote chapas que compõem o núcleo do estator foi montado de maneira que as ranhuras apresentem um ângulo de inclinação de 10º ao longo de toda a extensão da máquina. Para o rotor, foi projetado e construído um núcleo através do processo de metalurgia do pó utilizando como matéria-prima pó de ferro puro. A esse novo núcleo foram acrescentados ímãs de neodímio-ferro-boro. Após a montagem dos componentes, a máquina elétrica foi ensaiada em uma bancada de testes. Paralelamente com a confecção do núcleo foi efetuada a simulação computacional da máquina com três tipos diferentes materiais no núcleo do rotor. Os resultados encontrados indicaram que a metalurgia do pó é uma alternativa viável para produção do núcleo de máquinas elétricas. Entretanto alterações na topologia e na forma de fixação dos ímãs são necessárias para um melhor desempenho. / This work aims at the design, construction and performance analysis of a three-phase synchronous electric machine with a rotor core produced by powder metallurgy and neodymium-iron-boron magnets for application in wind turbines. Based on the electric machine VTOP model of the manufacturer Grupo Voges, changes were carried out in the constructive form of the stator and rotor cores. The bundle of plates that make the role of stator core were mounted with a 10º slope along the entire length of the machine. For the rotor, a core was designed and built by employing powder metallurgy process using pure iron powder as raw material. The neodymium-iron-boron magnets were added to this new core. After assembling the components, the electric machine was tested on a test bench. Simultaneously with the core fabrication, the machine was simulated with three different materials in the rotor core. The results indicated that powder metallurgy is a viable alternative to produce the core of electric machines. However, changes in the topology and shape of the magnets are necessary for better assembly, improving the performance.