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Fayyazi, Bahar [Verfasser], Oliver [Akademischer Betreuer] Gutfleisch, and Hadjipanayis [Akademischer Betreuer] George. "Development of Rare Earth Free and Rare Earth Balance Permanent Magnets / Bahar Fayyazi ; Oliver Gutfleisch, Hadjipanayis George." Darmstadt : Universitäts- und Landesbibliothek, 2021. http://d-nb.info/1238231705/34.
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Cedervall, Johan. "Synthesis and characterizationof rare earth free magnetic materialsfor permanent magnet applications." Thesis, Uppsala universitet, Institutionen för kemi - Ångström, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-200882.
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In this thesis the compounds Fe5SiB2 and Fe5PB2 have beensynthesized via high temperature synthesis, including arc melting anddrop synthesis. The structure for both compounds are of Cr5B3 typewith the space group I4/mcm. The cell parameters were refined toa = 5.5533 Å and c = 10.3405 Å for Fe5SiB2 and a = 5.4903 Å andc = 10.3527 Å for Fe5PB2. The saturation magnetization at roomtemperature for Fe5SiB2 has been measured to 138.8 Am2/kg and theanisotropy constant has been estimated to 79 kJ/m3. Theferromagnetic properties and the high anisotropy constant makesthese materials promising as permanent magnet materials, but moreinvestigations are necessary.
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Foeller, Philip York. "Novel materials and routes for rare-earth-free BaTiO3-based ceramics for MLCC applications." Thesis, University of Sheffield, 2017. http://etheses.whiterose.ac.uk/18954/.
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The NaNbO3-BaTiO3 (NNBT) solid solution was studied as a novel RE-free material for MLCC applications. Relaxor behaviour was found for NaNbO3 (NN)-concentrations as low as 2 mol%. The solid solution changes its behaviour with increasing NN-concentration from ferroelectric, to mixed ferroelectric-relaxor, to relaxor, to mixed behaviour again and finally ferroelectric. Broad permittivity profiles could therefore be obtained for a number of compositions with a wide range of Tmax, Na0.9Ba0.1Nb0.9Ti0.1O3 (90NNBT) possessed an industry standard (X7R) of TCC = ±15 % from -55 to 125 °C with low dielectric loss and a RT permittivity of ~ 800. Bilayers were then used to imitate CS microstructures and improve TCC. Optimisation of ‘core’-like material, i.e. BT, and a ‘shell’-like material, i.e. 2.5NNBT, in a bilayer at a volume ratio of 0.67 2.5NNBT with 0.33 BT resulted in a TCC of ±6% over the temperature range of 25 to 125 °C whilst maintaining a RT permittivity ~3000 and low dielectric loss. Utilising simulations of bilayer permittivity profiles reduced the number of trial and error compositions required to achieve permittivity and TCC targets. One limitation, however, was the interfaces that form, as they add an additional unaccounted component to the series model used. Their impact was reduced through careful processing. BT-2.5NNBT-90NNBT trilayers resulted in extended temperature range for low TCC applications, pushing the upper temperature up to over 150 °C. 0.33(BT)-0.33(2.5NNBT)-0.33(90NNBT) maintains a TCC of ±15 % to over 150 °C, with RT permittivity values above 100 and low dielectric loss. Adapted ternary phase diagrams were used to identify compositions that led to lower TCCs. Several important observations were drawn from the bi- and trilayer systems which suggested that that low TCC capacitors may be developed for any temperature range by the following protocols: (i) choose a temperature range, i.e. 100-200 °C; (ii) choose a material that possesses a Tmax of around 100 °C; (iii) choose a material with Tmax a little above 200 °C and (iv) choose a third material that possesses a Tmax that sits in the middle of the previous two materials, or has a broad shoulder that spans the gap between the other two Tmaxs. The number of materials are varied depending on the required temperature range. In general, the lowest number of materials that gives the required TCC should be chosen. This concept was tested for the creation of a temperature stable plateau 7 between 100 and 200 °C by a BT-85NNBT-90NNBT trilayer. The permittivity-temperature profile shows a plateau between ~100 and ~200 °C with permittivity changes of ~ ±10 % in that temperature range. Industrial MLCC prototypes based on the hypotheses from this work were made by AVX Ltd in Coleraine. The devices possessed comparable TCC and better lifetimes compared with equivalent commercial products.
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Cedervall, Johan. "Magnetic Materials for Cool Applications : Relations between Structure and Magnetism in Rare Earth Free Alloys." Doctoral thesis, Uppsala universitet, Institutionen för kemi - Ångström, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-331762.
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New and more efficient magnetic materials for energy applications are a big necessity for sustainable future. Whether the application is energy conversion or refrigeration, materials based on sustainable elements should be used, which discards all rare earth elements. For energy conversion, permanent magnets with high magnetisation and working temperature are needed whereas for refrigeration, the entropy difference between the non-magnetised and magnetised states should be large. For this reason, magnetic materials have been synthesised with high temperature methods and structurally and magnetically characterised with the aim of making a material with potential for large scale applications. To really determine the cause of the physical properties the connections between structure (crystalline and magnetic) and, mainly, the magnetic properties have been studied thoroughly. The materials that have been studied have all been iron based and exhibit properties with potential for the applications in mind. The first system, for permanent magnet applications, was Fe5SiB2. It was found to be unsuitable for a permanent magnet, however, an interesting magnetic behaviour was studied at low temperatures. The magnetic behaviour arose from a change in the magnetic structure which was solved by using neutron diffraction. Substitutions with phosphorus (Fe5Si1-xPxB2) and cobalt (Fe1-xCox)5PB2 were then performed to improve the permanent magnet potential. While the permanent magnetic potential was not improved with cobalt substitutions the magnetic transition temperature could be greatly controlled, a real benefit for magnetic refrigeration. For this purpose AlFe2B2 was also studied, and there it was found, conclusively, that the material undergoes a second order transition, making it unsuitable for magnetic cooling. However, the magnetic structure was solved with two different methods and was found to be ferromagnetic with all magnetic moments aligned along the crystallographic a-direction. Lastly, the origin of magnetic cooling was studied in Fe2P, and can be linked to the interactions between the magnetic and atomic vibrations.
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Islam, Md Zakirul. "Design and Performance Analysis of Rare-Earth-Free Five-Phase Permanent Magnet-Assisted Synchronous Reluctance Motor." University of Akron / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=akron1574423146588421.
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Cedervall, Johan. "Structure-Magnetism Relations in Selected Iron-based Alloys : A New Base for Rare Earth Free Magnetic Materials." Licentiate thesis, Uppsala universitet, Institutionen för kemi - Ångström, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-267575.
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Materials for energy applications are of great importance for a sustainable future society. Among these, stronger, lighter and more efficient magnetic materials will be able to aid mankind in many applications for energy conversion, for example generators for energy production, electric vehicles and magnetic refrigerators. Another requirement for the materials is that they should be made from cheap and abundant elements. For these reasons temperature induced magnetic transitions for three materials were studied in this work; one for permanent magnet applications and two magnetocaloric materials. Fe5SiB2 has a high Curie temperature and orders ferromagnetically at 760 K, providing possible application as a permanent magnet material. The ordering of the magnetic moments were studied and found to be aligned along the tetragonal c-axis and Fe5SiB2 undergoes a spin transition on cooling through a transition temperature (172 K), where the spins reorient along the a-axis in an easy plane. AlFe2B2 orders ferromagnetically at 285 K, making it a candidate for the active material in a magnetic refrigerator. The order of the magnetic transition has been studied as well as the magnetic structure. It was found that the magnetic moments are aligned along the crystallographic a-axis and that the magnetic transition is of second order. FeMnP0.75Si0.25 undergoes a first order magnetic transition around 200 K and the transition temperatures on cooling are different for the first cooling/heating cycle than for following cycles. This so called ”virgin effect” has been studied and found to originate from an irreversible structure change on the first cooling cycle through the ferromagnetic transition temperature.
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Anagnostopoulou, Evangelia. "A new route for rare-earth free permanent magnets : synthesis, structural and magnetic characterizations of dense assemblies of anisotropic nanoparticles." Thesis, Toulouse, INSA, 2016. http://www.theses.fr/2016ISAT0045/document.
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Cette thèse a eu pour objectif la préparation d’aimants nanostructurés sains terres rares à base d’un assemblage dense de nanobâtonnets de cobalt (Co NBs). Nous avons démontré la faisabilité d’un changement d’échelle du procédé polyol, avec des conditions d’agitation contrôlées, pour obtenir 5 g de NBs monodisperse. La modification de l’agent nucléant nous a permis de contrôler la taille et la forme des NBs conduisant à des valeurs élevées de champ coercitif. La réalisation d’aimants macroscopiques denses et robustes a été possible via la dispersion des bâtonnets dans du chloroforme et son évaporation sous champ magnétique à température ambiante. La valeur de (BH)max résultante a atteint dans le meilleur des cas une valeur de 165 kJ·m-3. Des résultats préliminaires sur la compaction d’assemblées de NBs montre que la fraction volumique magnétique peut être augmenté significativement (jusqu’à 30%). Cette étude prouve que l’approche « bottom-up» est très prometteuse pour obtenir des nouveaux matériaux magnétiques durs qui peuvent compléter le panorama des aimants permanents et combler le fossé entre les ferrites et les aimants NdFeBThe objective of this thesis is the preparation of nanostructured rare earth free permanent magnets based on dense assemblies of Co nanorods. We demonstrate the up-scaling of the polyol process for the synthesis of 5 g of monodispersed cylindrical Co NR with controlled cylindrical-like shape. Modification of the nucleating agent allows optimizing further the nanorods’ shape, leading to the highest coercivity values measured. Dense and robust macroscopic magnets were obtained via the rods’ alignment under a magnetic field presenting an ideal hysteresis loop. Additional structural and magnetic characterization was accomplished via small angle neutron scattering. A quantitative assessment of the (BH)max values showed a maximum of 165 kJ·m-3. Preliminary compaction experiments resulted in the fabrication of bulk magnets with increased magnetic volume fraction (up to 30%). We prove that the bottom-up approach is very promising to get new hard magnetic materials that can compete in the permanent magnet panorama and fill the gap between the ferrites and the NdFeB magnets
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Patel, Ketan. "OXIDE BASED MAGNETIC NANOCRYSTALS FOR HIGH-FREQUENCY AND HIGH-ENERGY PRODUCT APPLICATIONS." Master's thesis, Temple University Libraries, 2017. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/464990.
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Mechanical EngineeringM.S.M.E.
Magnets play a major role in our rapidly developing world of technology. Electric motors and generators, transformers, data storage devices, MRI machines, cellphones, and NMR are some of the many applications for magnets. However, almost all the magnets currently being used have rare-earth heavy metals in them. Despite their high-energy product, the presence of rare-earth metals increases the cost significantly. Also, the processes involved in the mining of rare-earth metals are hazardous to the environment, and to all life forms. In the past few decades, oxide based magnets have gained a lot of attention as potential replacements for the rare-earth magnets. Oxide based magnetic nanocrystals are attracting a lot of attention as a potential replacement for rare-earth magnets. They are stable in ambient condition and their manufacturing cost is very low when compared to the rare-earth magnets. My work deals with the synthesis of core-shell magnetic structure for high frequency applications (Chapter 1) and the synthesis of high energy product magnetic nanocrystals (Chapter 2) and the synthesis of soft magnetic nanocrystals for high frequency measurement. NiZn ferrite, a soft oxide based magnet cannot be directly implied at high frequencies as they fail at the frequency which over the MHz range. On the other hand, BaZn ferrite is a Y-type magnets, which is robust at higher frequencies. Therefore, using the latter magnet as a protective shell for core material, made of former magnet, enables us to manufacture a cheap solution to the rare-earth magnets used in our cell phones and other devices that work on high frequency signals. On the other hand, successful coating of a very soft magnetic material on a hard-magnetic core increases the total energy product of the magnetic composite, which enhances its versatility.
Temple University--Theses
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Bechtel, Tom B. "Electrochemical partitioning of actinides and rare earths in molten salt and cadmium solvents : activity coefficients and equilibrium simulation /." free to MU campus, to others for purchase, 1997. http://wwwlib.umi.com/cr/mo/fullcit?p9841263.
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Pei, Min. "Effects of Lanthanum doping on the microstructure and mechanical behavior of a SnAg alloy." Diss., Available online, Georgia Institute of Technology, 2007, 2007. http://etd.gatech.edu/theses/available/etd-03272007-120709/.
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Thesis (Ph. D.)--Mechanical Engineering, Georgia Institute of Technology, 2007.Neu, Richard W., Committee Member ; Sanders, Thomas H. Jr., Committee Member ; Wong, C.P., Committee Member ; McDowell, David L., Committee Member ; Qu, Jianmin, Committee Chair.
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Boonsin, Rachod. "Développement de luminophores sans terres rares pour l'éclairage éco-énergétique à base de diodes électroluminescentes." Thesis, Clermont-Ferrand 2, 2016. http://www.theses.fr/2016CLF22704/document.
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Les luminaires à LEDs représentent une alternative "verte" aux lampes fluorescentes et aux lampes à incandescence en répondant notamment à des critères de préservation de l'environnement : réduction de la consommation d’énergie, technologies sans mercure ni plomb et recyclables à 98%. Cependant, ces luminophores, qui sont actuellement utilisés dans les luminaires à LEDs, contiennent aujourd’hui des éléments de terres rares qui sont issus à 95% de Chine, créant de ce fait une situation de quasi-monopole et un risque réel pour le déploiement de la technologie LED dans les années à venir. Dans le cadre de cette thèse, nous nous sommes intéressés au développement de luminophores sans terres rares pour produire de la lumière blanche dans les luminaires à LEDs. Au cours de ces travaux nous avons étudié trois types de luminophores sans terres rares: luminophores organiques, luminophores hybrides (organiques-inorganiques) et quantum dots (QDs) type cœur-coquille. Les études optiques réalisées sur ces luminophores sous excitation LEDs UV ou bleue nous ont permis de déterminer leurs caractéristiques colorimétriques (IRC, T(K), PLQY(%)) et de mettre en évidence l’évolution de leurs performances dans les conditions d’usage. Pour obtenir une lumière la plus proche du blanc idéal, les luminophores les plus performants ont été sélectionnés puis mélangés en proportion adéquate avec une matrice polymère de type silicone pour conduire à un film composite offrant une émission blanche de qualité sous excitation LEDs UV ou bleue. Un autre volet de ce travail a été dédié à l’étude de la stabilité de ces luminophores (films ou poudres) en fonction du temps et de la température. L’influence de ces paramètres sur les propriétés optiques a été déterminée. Des performances optiques de 30% ont été enregistrées avec des caractéristiques photométriques intéressantes. Aussi, l’ensemble des résultats obtenus montre l’intérêt de poursuivre ces études sur les luminophores sans terres rares qui offrent des propriétés optiques intéressantes. Même s'ils ne concurrencent pas encore les luminophores inorganiques pour l’application « éclairage grand public », les luminophores sans terres rares peuvent déjà se positionner sur d’autres secteurs d’activité comme par exemple : l’éclairage d’ambiance, la signalétique le marquage anti-contrefaçonsLighting technologies based on light-emitting diodes have become an alternative solution over the obsolete technologies (fluorescent lamps and incandescent lamps) due to their positive key criteria of environmental conservation: reduction of energy consumption and mercury/lead-free with 98% recycling technologies. However, the rare-earth elements, which are currently used in LED lightings, are produced by China at about 95%, thereby creating a monopoly situation on the rare-earth elements’ market and also a risk to the deployment of LED technologies in coming years. In this work, we have been interested in the development of rare-earth-free luminescent materials for LED lighting applications in order to produce a white light emission. Three kinds of rare-earth-free luminescent materials have been investigated: organic phosphors, hybrid (organic-inorganic) phosphors and core-shell quantum dots (QDs). The optical studies of these phosphors recorded upon UV and/or blue excitations allow us to determine their colorimetric parameters (CRI, T(K), PLQY(%)) and to demonstrate their optical performances for use in lighting devices. In order to yield a color emission close to ideal white light, the best phosphors were selected and then introduced by mixing them in appropriate proportions into silicone polymers. Another part of this work was devoted to the studies of stability of phosphors (films or powders) under operating conditions of LEDs, moreover, variation of their optical properties as a function of time and temperature were also determined. The optical performances about 30% have been recorded with some interesting colorimetric parameters. Although these materials have presented lower photoluminescence properties compared with commercial rare-earth based inorganic phosphors for “public lighting” applications, they can already be positioned on other luminescent sectors such as indoor lighting, signage anti-counterfeit marking
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Sadiq, Muhammad. "Design and fabrication of lanthanum-doped Sn-Ag-Cu lead-free solder for next generation microelectronics applications in severe environment." Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/44762.
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Sn-Pb solder has long been used in the Electronics industry. But, due to its toxic nature and environmental effects, certain restrictions are made on its use and therefore many researchers are looking to replace it. Sn-3.0Ag-0.5Cu (SAC) solders are suggested as lead-free replacements but their coarse microstructure and formation of hard and brittle Inter-Metallic Compounds (IMCs) like Ag₃Sn and Cu₆Sn₅ have limited their use in high temperature applications. In this research work, RE elements, mostly lanthanum (La), are used as potential additives to SAC alloys. They reduce the surface free energy, refine the grain size and improve the mechanical and wetting properties of SAC alloys. An extensive experimental work has been performed on the microstructure evolution, bulk mechanical properties, individual phase (matrix and IMCs) mechanical properties, creep behavior and wettability performance of the SAC and SAC-La alloys, with different (La) doping. SEM and EDS have been used to follow the continuous growth of the IMCs at 150°C and 200°C and thus provide a quantitative measure in terms of their size, spacing and volume fraction. Grain size is measured at regular intervals starting from 10 hours up to 200 hours of thermal aging using Optical Microscope with cross polarized light. Bulk mechanical properties are evaluated using tensile tests at low strain rates. Individual phase mechanical properties like Young's modulus, hardness, strain rate sensitivity index and bulge effects are characterized with nanoindentation from 100 µN up to 5000 µN loadings at different temperatures of 25°C, 45°C, 65°C and 85°C. Creep experiments are performed at elevated temperatures with good fitting of Dorn creep and back-stress creep models. Activation energy measurements are made at 40°C, 80°C and 120°C. Wettability testing on copper substrates is used for surface tension, wetting force and contact angle measurements of SAC and SAC-La doped alloys at 250°C and 260°C.
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Tyrman, Muriel. "Vers une alternative aux aimants à base de terres rares : hexaferrites nanostructurés et alliages Mn-Al." Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLV022.
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Dans le cadre d'un projet de transport automobile propre pour la mise en place de véhicules électriques décarbonés grand public, les aimants représentent un enjeu important au niveau des moteurs électriques. Il est alors nécessaire de se passer des aimants à base de terres rares, peu écologiques et dont un seul pays détient le monopole. Deux voies sont explorées ici : la nanostructuration des hexaferrites de type M par frittage flash de type SPS (Spark Plasma Sintering), et la synthèse d'alliages Mn-Al-C par la méthode de la trempe rapide sur roue. Concernant le premier matériau, l'optimisation du protocole de synthèse a permis d'augmenter le champ coercitif d'un facteur 2. Deux outils de caractérisation des aimants ont été mis en place : le premier évalue la texture du matériau (modèle de Stoner et Wohlfarth), le second étudie les processus d'aimantation (Preisach). Pour les alliages Mn-Al-C, nous avons pu démontrer la présence d'un couplage antiferromagnétique entre les atomes de Mn des sites 1a et 1d. La diffraction de neutrons à également pu montrer que le moment magnétique du Mn du site 1d est par ailleurs très supérieur à celui du site 1a. Un broyage cryogénique suivi d'un frittage SPS à haute pression (400 MPa) a permis d'augmenter la valeur du champ coercitif de 40 %. Les résultats obtenus sont très prometteurs quant à la faisabilité d'alternatives aux aimants à base de terres raresIn the context of green car development for mass market, development of low cost rare-earth-free magnets is clearly a milestone, because the rare-earth are expensive and their production is not ecological and a monopoly of one country. Two routes are explored herein : nanostructuration of M-type hexaferrites by flash sintering (Spark Plasma Sintering), and the synthesis of Mn-Al-C alloys by melt spinning. Concerning the first material, the optimization of the synthesis protocol allowed to increase the coercive field by a factor of 2. Two characterization tools of the magnets were set-up : the first evaluates the texture of the material (Stoner and Wohlfarth model), the second, based on Preisach model, is used to infer the magnetization processes. For Mn-Al-C alloys, we have evidenced from Weiss plots the antiferromagnetic coupling between 1a and 1d-sites Mn atoms. Neutron diffraction confirmed this result and shown that the magnetic moment of the 1d-site Mn is also much larger than that of 1a-site. Cryogenic ball milling followed by high-pressure SPS (400 MPa) increased the coercive field by 40 %. The results obtained are very promising as to the feasibility of alternatives to rare-earth magnets
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Legentil, Paul. "Développement de poudres hybrides "Hydroxydes Doubles Lamellaires-luminosphores" sans terres rares. Intégration dans des revêtements composites compatibles avec des sources d'excitation LED." Thesis, Université Clermont Auvergne (2017-2020), 2020. http://www.theses.fr/2020CLFAC013.
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Ces travaux de thèse ont pour ambition de proposer des solutions alternatives, aux luminophores avec terres rares, offrant des performances convenables pour des applications dans des dispositifs à LED comme l’éclairage mais également la visualisation ou encore le marquage ou la signalétique. Nous nous sommes intéressés à des luminophores organiques mais également inorganiques tels que les quantum dots (QD). Le problème majeur de ces familles de luminophores est leur instabilité sous contrainte thermique et/ou photonique. Aussi, afin de pallier ce problème nous avons choisi d’utiliser des matériaux inorganiques plaquettaires de type « hydroxyde doubles lamellaires » (HDL) comme matrice hôte du luminophore. Les luminophores étudiés sont la fluorescéine, la sulforhodamine B et des quantum dots InP/ZnS. Plusieurs techniques expérimentales ont été utilisées afin de caractériser leurs propriétés structurales et morphologiques (DRX, SAXS, IR, MEB, MET…). Les propriétés optiques ont également été enregistrées (émission, excitation, rendement quantique de photoluminescence, déclins…). Ces travaux ont mis en évidence la plus-value de la matrice HDL qui permet de reproduire un effet de solvatation pour le luminophore organique ou QD dans une matrice solide et de retrouver des propriétés d’émission semblables à celles de ces luminophores en solution diluée. La dispersion dans une matrice silicone est également favorisée et la stabilité de ces revêtements composites (HDL-Luminophore/silicone) sous différentes contraintes est nettement amélioréeThese works have the ambition to offer alternative solutions to phosphors with rare-earth elements, displaying suitable performance for LED devices applications as well as signage or display applications. We have been interested in organic as well as inorganic phosphors such as quantum dots (QD). The main problem encountered with these compounds is their relative instability under thermal and/or photonic stresses. Thus, in order to overcome this issue, we decided to use inorganic materials called layered double hydroxide (LDH) as host matrix to protect these phosphors. Several experimental techniques (XRD, SAXS, IR, SEM, TEM…) have been used to characterize structural and morphological properties. Optical properties have also been recorded (emission and excitation spectra, photoluminescence quantum yields, fluorescence decay…). Using extremely small amounts of phosphors, it is demonstrated here that Zn2Al cation-based LDH tethering acts as a «solid solvent» for the dye, enabling its luminescence even in powder form. Additionally, LDH platelets are found to help the dispersion of the dye or QD in silicone to obtain homogeneous composite films, which exhibit luminescent properties. Finally, the stability of composite coatings (LDH-phosphor/silicone) under different stresses (thermal and photonic) is most often improved
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Bittner, Florian. "Untersuchung der Wechselwirkung von Verarbeitung, Gefüge und Eigenschaften hartmagnetischer Mn-Al-Legierungen mit L1 0-Struktur." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2018. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-231582.
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Die vorliegende Arbeit behandelt die Wechselwirkung von Verarbeitung und Gefüge Mn-Al basierter hartmagnetischer Werkstoffe sowie die Auswirkung des Gefüges auf deren Eigenschaften. Dabei wurde das Gefüge der metastabilen tau-Phase im Anschluss an die Phasenbildung aus der Hochtemperaturphase epsilon-MnAl und die Auswirkung einer anschließenden Umformung untersucht. Der Schwerpunkt der Arbeit lag in der Analyse der Evolution verschiedener Gefügebestandteile, wie Grenzflächenverteilung, Versetzungen und Korngröße unter Verwendung von Rasterelektronenmikroskopie und Elektronenrückstreubeugung.
Die epsilon-tau Umwandlung kann auf 2 verschiedene Routen erfolgen. In beiden Fällen wird die Bildung von 3 kristallographisch unterschiedlichen zwillingsähnlichen Defekten beobachtet, die als wahre Zwillinge, Ordnungszwillinge und Pseudozwillinge bezeichnet werden. Sie lassen sich als Rotationen um einen kristallographischen {111}-Pol beschreiben. Der Anteil der Zwillingsdefekte nach der Umwandlung, aber auch die Korngröße und Versetzungsdichte sind von der gewählten Umwandlungsroute abhängig. Während die Sättigungspolarisation annähernd gleich ist, reagiert die Koerzitivfeldstärke sensitiv auf den Gefügezustand. Eine niedrige Korngröße und hohe Versetzungsdichte tragen zu ihrer Erhöhung bei.
Eine anschließende Kaltumformung erzeugt ein vielfach verzwillingtes Verformungsgefüge mit hoher Koerzitivfeldstärke. Wärmebehandlungen und die Analyse der Schärfe von Kikuchi-Beugungsbildern haben gezeigt, dass nicht die hohe Zwillingsdichte, sondern primär Versetzungen im Verformungsgefüge die Koerzitivfeldstärke steigern. Warmumformung von tau-MnAl führt zur dynamischen Rekristallisation. Die Kinetik der Gefügeneubildung und die resultierende Korngröße sind stark von der Umformtemperatur abhängig. Durch Umformung lässt sich eine kristallographische Texturierung von tau-MnAl erreichen. Die Orientierung der magnetisch leichten [001]-Richtung ist dabei vom gewählten Umformverfahren und gegebenenfalls von der Nachbehandlung abhängig. Statische und dynamische Rekristallisation reduzieren den Anteil der Zwillingsdefekte signifikant und besonders Pseudozwillinge und Ordnungszwillinge werden im Gefüge beseitigt. Das Rekristallisationsgefüge weist gegenüber dem Umwandlungsgefüge einen geringeren Widerstand gegen die mit der Zersetzungsreaktion verbundene Bildung von beta-Mn auf. Die Ursache liegt in einer selektiven beta-Mn-Bildung an allgemeinen Korngrenzen, während die Zwillingsdefekte einen erhöhten Widerstand gegen sie Zersetzung aufweisen.
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Fegy, Karine. "Ingénierie de matériaux moléculaires magnétiques : complexes de radicaux libres nitronyl nitroxydes bis-bidentes ; synthèse, structure et magnétisme." Université Joseph Fourier (Grenoble ; 1971-2015), 1997. http://www.theses.fr/1997GRE10197.
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La chimie de coordination des radicaux libres nitronyl nitroxydes est propice aux composes moleculaires magnetiques (aimants moleculaires ou transitions de spin). Cependant le caractere base de lewis faible du groupe nitroxyde >n-o limite dans de nombreux cas leur utilisation aux ions metalliques porteurs de ligands attracteurs. Pour eviter ce probleme, nous avons choisi de substituer les radicaux par des groupes donneurs. Ce travail concerne la synthese, la caracterisation structurale et l'etude des proprietes magnetiques de complexes d'ions metalliques avec les radicaux nitronyl nitroxydes porteurs des groupes imidazolyle (nitimh) ou benzimidazolyle (nitbzimh). La premiere partie est consacree a la complexation des radicaux non deprotones. Avec les ions metalliques de transition mn#2#+, ni#2#+, zn#2#+ et de terres rares gd#3#+, dy#3#+, plusieurs molecules mononucleaires qui sont des entites discretes, ont ete isolees. Leurs structures determinees par diffraction des rayons x sur monocristal montrent pour la premiere fois des centres metalliques entoures exclusivement de radicaux nitroxydes ; m(l)#3(mn#2#+, ni#2#+, zn#2#+) ou m(l)#4 (gd#3#+, dy#3#+)(l = nitimh ou nitbzimh). L'etude de leurs proprietes magnetiques revele des comportements varies. La seconde partie du travail decrit une serie de composes etendus du manganese(ii), obtenus lorsque les radicaux sont deprotones ; nitim#- ou nitbzim#-. La dimension des composes depend alors des conditions experimentales de deprotonation et du type de contre anions utilises. Quatre chaines ferrimagnetiques dans lesquelles alternent les ions manganese(ii) et les radicaux ont ete isolees, et leurs structures determinees. L'etude de leurs proprietes magnetiques met en evidence une aimantation spontanee au-dessous de temperature comprises entre 2 k et 4,5 k. Selon des conditions experimentales differentes, une serie de composes bidimensionnels a egalement ete synthetisee. La determination structurale de l'un d'entre eux montre qu'il s'agit de composes lamellaires constitues de feuillets mn#2(l)#3#+, separes par les contre anions. Ces composes sont des aimants en dessous de temperatures allant de 1,4 k a 40 k. Cette strategie est donc prometteuse et devrait ouvrir de nouvelles perspectives pour la construction d'edifices tridimensionnels.
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Kinuthia, Wanyee. "“Accumulation by Dispossession” by the Global Extractive Industry: The Case of Canada." Thèse, Université d'Ottawa / University of Ottawa, 2013. http://hdl.handle.net/10393/30170.
Full textAbstract:
This thesis draws on David Harvey’s concept of “accumulation by dispossession” and an international political economy (IPE) approach centred on the institutional arrangements and power structures that privilege certain actors and values, in order to critique current capitalist practices of primitive accumulation by the global corporate extractive industry. The thesis examines how accumulation by dispossession by the global extractive industry is facilitated by the “free entry” or “free mining” principle. It does so by focusing on Canada as a leader in the global extractive industry and the spread of this country’s mining laws to other countries – in other words, the transnationalisation of norms in the global extractive industry – so as to maintain a consistent and familiar operating environment for Canadian extractive companies. The transnationalisation of norms is further promoted by key international institutions such as the World Bank, which is also the world’s largest development lender and also plays a key role in shaping the regulations that govern natural resource extraction. The thesis briefly investigates some Canadian examples of resource extraction projects, in order to demonstrate the weaknesses of Canadian mining laws, particularly the lack of protection of landowners’ rights under the free entry system and the subsequent need for “free, prior and informed consent” (FPIC). The thesis also considers some of the challenges to the adoption and implementation of the right to FPIC. These challenges include embedded institutional structures like the free entry mining system, international political economy (IPE) as shaped by international institutions and powerful corporations, as well as concerns regarding ‘local’ power structures or the legitimacy of representatives of communities affected by extractive projects. The thesis concludes that in order for Canada to be truly recognized as a leader in the global extractive industry, it must establish legal norms domestically to ensure that Canadian mining companies and residents can be held accountable when there is evidence of environmental and/or human rights violations associated with the activities of Canadian mining companies abroad. The thesis also concludes that Canada needs to address underlying structural issues such as the free entry mining system and implement FPIC, in order to curb “accumulation by dispossession” by the extractive industry, both domestically and abroad.
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Fayyazi, Bahar. "Development of Rare Earth Free and Rare Earth Balance Permanent Magnets." Phd thesis, 2021. https://tuprints.ulb.tu-darmstadt.de/19208/1/Disseration%20Bahar%20Fayyazi.pdf.
Full textAbstract:
In the quest for a sustainable permanent magnetic material, two material systems were extensively studied. The first part of the thesis investigates the Fe-Sn based systems as potential RE-free candidates. The Fe-Sn binary and several multinary systems such as (FeX)5Sn and (FeX)3(SnY) were extensively screened for the discovery of a new hard magnetic material using high-throughput Reactive Crucible Melting (RCM) technique as well as other non-equilibrium methods. The follow-up experimental screening strategies were supported by theoretical calculations carried out by other scientists. For high-throughput characterization, these synthesis techniques were combined with energy dispersive X-ray spectroscopy as well as magneto-optical Kerr microscopy which enabled the identification of phases with uniaxial magnetic anisotropy, for example Fe3Sn2 in the binary system. The reliability of the reactive crucible melting method was evaluated by a comparison of the phases forming in the reactive crucible with phases appearing in conventionally melted samples. It has been shown that under some circumstances, the phase relations might not always be correctly reproduced. The Fe5Sn3 phase, existing in the equilibrium phase diagram at 800°C and forming in conventionally melted alloys, does not exist in the diffusion zone of the reactive crucible. The problem of "missing phases" is discussed. In addition, by observation of domain structure and by employing different analytical models based on domain theory, the anisotropies of phases with uniaxial anisotropy were evaluated. It has been shown that the consideration of the magnitude of anisotropy is crucial for the selection of a proper model and realistic assessment of anisotropy energy. With the example of materials with high and intermediate uniaxial anisotropy, the applicability of 3 analytical models "Kittel", "Szymczak" and "Bodenberger-Hubert" were investigated.
Another major activity to study the Fe-Sn system was the investigation of structural and intrinsic magnetic properties of its binary ferromagnetic compounds by synthesis and characterization of Fe3Sn, Fe5Sn3, and Fe3Sn2 single crystals. Derived from single crystal X-ray diffraction and Transmission Electron Microscopy (TEM), a new structural model is proposed for the Fe5Sn3 crystals - the threefold twinning of an orthorhombic unit cell with (3+1) dimensional space group Pbcm(α00)0s0. The spontaneous magnetization (Ms) and the anisotropy constants K1 and K2 of Fe3Sn, Fe5Sn3, and Fe3Sn2 single crystals were determined in a wide temperature range using M(H) dependencies and the Sucksmith-Thompson technique. A large however planar anisotropy of K1 = -1.16 MJm-3 appreciable for a rare earth free system and a negligible uniaxial anisotropy of K1 = +0.05 MJm-3 were evaluated for Fe3Sn and Fe3Sn2 compounds, respectively.
The second part of the thesis investigates the effect of partial substitution of Ce and Co in the Nd-Fe-B system. By synthesis and characterization of (Nd1-xCex)2(Fe1-yCoy)14B single crystals, the structural and intrinsic magnetic properties were investigated for y = 0 and x = 0, 0.15, 0.36, 0.63 and 1 as well as y = 0.1 and x = 0 and 0.15. The effect of doping with Ce and Co on crystal lattice parameters a and c, Ms, Ha, TC, TSPT, and K1 were evaluated. Additionally, for Nd2Fe14B and by analysis of single crystal magnetization curves measured under the field of up to 50 T along four different orientations, five associating anisotropy constants were extracted using theoretical models and based on minimization of the total energy of the system.
All intrinsic magnetic properties were gradually decreased by an increase in Ce proportion when it was solely introduced to the structure. Furthermore, Ce substitution resulted in a decrease in spin reorientation transition temperature where anisotropy switches from uniaxial to an easy cone. The addition of Co has not only increased the Curie temperature but also improved the thermal stability of the intrinsic magnetic properties. The reduction of anisotropy energy with Ce substitution could partially be compensated by co-doping together with Co, especially at high temperatures. The improved intrinsic properties of the co-doped Nd2Fe14B was also reflected in their extrinsic magnetic properties by characterization of mechanochemically synthesized sub-micron particles. For the sample with (Nd0.82Ce0.18)2(Fe0.85Co0.15)14B composition, an improved temperature coefficient of coercivity of β = -0.4 %/K was achieved. Comparing these results with single crystal data, it can be verified that the enhanced high-temperature performance of NdFeB-based magnets co-doped with Ce and Co, which have also been observed in various literature, is due to an improvement in intrinsic magnetic properties.
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Mohseni, Farzin. "Nanostructured rare-earth free permanent magnets." Doctoral thesis, 2021. http://hdl.handle.net/10773/31064.
Full textAbstract:
In this work we explore on the rare-earth free nanostructured permanent
magnets, including thin films, nanoparticles and nanocomposites with the focus
on Alnico magnets and hexaferrites. Here we investigate the effects of different
heat treatment conditions on structural and magnetic properties of RFsputtered
Alnico V thin films on Si substrates. We show an in-depth analysis of
the various heat treated samples with high coercivity to unveil the origin of high
coercivity in these thin films with a recently discovered Fe-Co rich Body-
Centered Tetragonal (bct) phase. Exchange-spring magnets are also explored,
namely barium hexaferrite (BaM) and strontium hexaferrite (SrM). We
investigate on the possibility of coating BaM and SrM flake-like hexaferrite
particles via a hydrothermal and coprecipitation method to prepare core-shelllike
BaM/Fe3O4 and SrM/Fe3O4 nanocomposites, where the ferrite particles
where prepared via a sol-gel auto-combustion method. We show how
optimised hard to soft magnetic phase ratio and preparation conditions lead to
a significant enhancement in their hard magnetic properties compared to
commercial ferrite powders. Moreover, we employ the prepared highperformance
exchange-coupled nanocomposite powder and investigate the
mechanical and magnetic properties of warm compressed nanocomposite
powder in an epoxy matrix. We show how the powder-to-resin ratio and
preparation conditions lead to optimised mechanical properties, and
enhancement in the maximum energy product of the composite magnet.
Finally, micromagnetic simulations were employed to better understand and
support the experimental results of the exchange coupling behaviour of the
BaM/Fe3O4 hard-soft magnetic nanocomposites. We show how the thickness of
BaM particles affect their coercivity and how the volume fraction of each
magnetic phase, together with their interface area, affect the exchange
coupling behaviour and maximum energy product of the nanocomposite
magnets.Neste trabalho, exploramos magnetes permanentes nano-estruturados, livres de terras raras, incluíndo filmes finos, nanopartículas e nanocompósitos focando magnetes de Alnico e hexaferrites. Investigamos os efeitos de diferentes condições de tratamento térmico nas propriedades estruturais e magnéticas de filmes finos de Alnico V pulverizados por RF em substratos de Si. Fizemos uma análise mais aprofundada das várias amostras tratadas termicamente para desvendar a origem da alta coercividade nesses filmes finos com uma recentemente descoberta fase Tetragonal Centrada no Corpo (bct) rica em Fe-Co. Os magnetes exchange-spring também são explorados, e.g. hexaferrite de bário (BaM) e hexaferrite de estrôncio (SrM). Investigamos a possibilidade de revestir partículas de hexaferrite semelhantes a flocos de BaM e SrM por meio de métodos hidrotérmico e de coprecipitação para preparar nanocompósitos tipo núcleo-casca de BaM/Fe3O4 e SrM/Fe3O4, onde as partículas de ferrite foram preparadas por meio de método sol-gel de combustão. Mostramos como a relação de fases magnéticas macia e dura, mais as condições de preparação otimizadas, levam a um aprimoramento significativo das suas propriedades magnéticas duras em comparação com pós de ferrite comerciais. Além disso, usando o pó de nanocompósito de alto desempenho, investigamos as propriedades mecânicas e magnéticas do pó do nanocompósito comprimido a quente em uma matriz de epóxi. Mostramos como a combinação pó-resina e as condições de preparação levam à obtenção de propriedades mecânicas otimizadas e a um aprimoramento do produto de energia máxima do magnete composto. Finalmente, realizamos simulações micromagnéticas para melhor compreender e apoiar os resultados experimentais do comportamento de acoplamento de troca dos nanocompósitos magnéticos duros-macios de BaM/Fe3O4. Mostramos como a espessura das partículas BaM afetam a coercividade e como a fração de volume de cada fase magnética, assim como a área de interface entre elas, afetam o comportamento de acoplamento de troca bem como o produto energético máximo dos magnetes de nanocompósitos.
Programa Doutoral em Ciência e Engenharia de Materiais
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Tsai, Meng-Tsen, and 蔡孟岑. "Oxidation and Corrosion Behaviour of Rare-Earth Elements Containing Lead-Free Solders." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/85261268057361837368.
Full textAbstract:
碩士國立雲林科技大學
材料科技研究所
99
This study investigated the corrosion and oxidation effects on different contents of rare-earth elements (Mm) in lead-free solders Sn-3Ag-0.5Cu-XMm and Sn-3Ag-0.5Cu-4Ti-XMm alloys. The composition and structure of the oxidation layers in the high temperature atmospheric environment or corrosive environment of 3.5 wt.% NaCl solution were analyzed. In high temperature atmospheric environment, the growth rate of oxidation layer of Sn-3Ag-0.5Cu-XMm and Sn-3Ag-0.5Cu-4Ti-XMm alloys with 0.05 wt.% and 0.1 wt.% of rare-earth elements was lower than the alloys with 0 wt.%、0.2 wt.% and 0.5 wt.% of rare-earth elements. The addition of a trace amount of rare-earth elements into solders caused heterogeneous nucleation and grain size reduction of the matrix β-Sn and improved the oxidation and corrosion resistance of solders.The high concentration of rare-earth element in Sn-3Ag-0.5Cu-XMm and Sn-3Ag-0.5Cu-4Ti-XMm alloys caused the formation of LaSn3 intermetallic compound, on which Sn-whisker grew up easily. Thus, it reduced the oxidation and corrosion resistance of solders In high temperature atmospheric environment, while adding 4wt.% of titanium in Sn-3Ag-0.5Cu-4Ti-XMm alloy, a thin and uniform oxidation layer of TiO or TiO1+X formed on the alloy surface. The thin and uniform oxidation film of TiO or TiO1+X hindered the diffusion of oxygen into the matrix β-Sn of alloy, prevented tin-oxide forming, and reduced the oxidation rate of Sn-3Ag-0.5Cu-4Ti-XMm alloy. In 3.5wt.% NaCl solution, the corrosion potential (Ecorr) of Sn-3Ag-0.5Cu-XMm and Sn-3Ag-0.5Cu-4Ti-XMm lead-free solders with 0.05 wt.% and 0.1 wt.% of rare-earth elements was higher than the solders with other concentrations of rare-earth elements. In comparison with the Sn-3Ag-0.5Cu-XMm alloy without Ti containing, the Sn-3Ag-0.5Cu-4Ti-XMm alloy with 4 wt.% Ti has a higher corrosion potential (Ecorr) and a lower corrosion current density (Icorr). The results revealed that the addition of 4 wt.% Ti and rare-earth elements between 0.05 wt.% to 0.1 wt.% in Sn-3Ag-0.5Cu reduced the corrosion rate and improved the corrosion resistance of lead-free solders. Similar results were found in oxidation tests.
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LIN, JI-SYUAN, and 林季萱. "The Study of Characteristic under add Rare-Earth Element to Free-Leads-Copper Alloy." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/c4a486.
Full textAbstract:
碩士建國科技大學
機械工程系暨製造科技研究所
105
In this study, lead-free Brass 64 alloys were used as the base material. 18.3% Ca, 45% Si, 30.1% Re, 0.12% C and 0.005% S were smelted at 1,200 ° C and poured into the stretched resin module and wet sand mold as a model of fluidity analysis and the test of mechanical properties. Results show that adding brass 64 with rare earth alloy 3% (200ppm), 5% (400ppm), 10% (600ppm) has no negative effect on fluidity. When rare earth alloys contain silicon metal, the tensile strength increases from 16kg /〖mm〗^2 to 18kg /〖mm〗^2, and the elongation rate increases from 10% to 12% along with the content increasing. Moreover, adding rare earth alloy with silicon element can produce Cu2Si medium metal compounds and the hardness increases as the silicon elements increase.
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Tsai, Yu-Peng, and 蔡鈺芃. "Tensile properties of Sn-Ag-Cu lead-free solders with rare earth in high temperature." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/90746364725139379147.
Full textAbstract:
碩士國立臺灣大學
材料科學與工程學研究所
96
The tensile properties of Sn-3wt％Ag-0.5wt％Cu-0.05 wt％Ce, Sn-3wt％Ag-0.5wt％Cu-0.05 wt％Ce and Sn-3wt％Ag-0.5wt％Cu-0.05 wt％Ce-0.2wt％Zn were investigated and compared with those of a Sn-Ag-Cu solder. The tensile strength of each solder decreases with increasing test temperature, and decreasing strain rate.The ductility of each lead-free solder keeps stable value in the strain rate from 1×10-4mm/s to 1×10-3mm/s and in the test temperature ranging from 30℃ to 150℃. Coarsing β-Sn grains and dendrite grains are formed in Sn-3Ag-0.5Cu, especially bigger Ag3Sn and Cu6Sn5 intermetallic compounds(IMCs) were found in Sn-3Ag-0.5Cu alloy.With addition of different content rare earth(Ce) element the dendrite grains were refined, at the same time, Ag3Sn and Cu6Sn5 intermetallics were finer according to the adsorption affection of the active rare earth elements.It was found easier formation and faster growth of voids at the coarsing IMCs by the lower tensile rate at a higher temperature.Voids and cavities were observed along grain boundaries in Sn-3Ag-0.5Cu-0.5Ce.More coursing rare earth IMCs had the same affection, they would resulted in excess stress concentration, the crack and cavity might be nucleated near the impurity particles along the grain boundaries. Adding adequate Ce could improved mechanical properties, the tensile strength were enhanced, but excess adding brought negative affection.In addition, the alloy with the addition of trace Zn, it restricted the growth of Ce IMCs. The mechanical properties were also enhanced. All these results indicated that adding trace rare earth element and Zn was an efficient way to develop tensile properties for the new solders.
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Chieh-SzuHuang and 黃捷思. "Non-Rare Earth and Fluoride-Free Red Emitting Phosphor: A combined Experimental and Ab Initio Study." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/442f23.
Full textAbstract:
碩士國立成功大學
電機工程學系
104
Red light phosphor is the key component for stimulating natural sunlight LEDs. Recent years, Mn4+ luminescence centers are commonly used to substitute environmentally hazardous rare-earth dopants. However, the choice of matrix materials is usually fluoride compound, e.g. K2TiF6, which derivate contaminate issues on silicon industry. In this paper, the ecofriendly “rare-earth-free” and “flouoride-free” red light luminance material, Mg2TiO4 (MTO) with the luminescent center of Mn4+ (MTO:Mn), is investigated. The atomistic models were constructed using ab initio calculations based on density functional theory. The density of states of MTO:Mn with varies potential sensitizers reveal that the best candidate for sensitizer is niobium (Nb). In addition, phosphors were fabricated via solid state sintering. X-ray diffraction spectrum shows no meta-stable phase and photoluminescence spectrum indicates the intensity of light is around 243% after sensitization. This report successfully proposes a novel method to understand optoelectronic properties of phosphors and in turn obtain desirable products. In addition, Mg2TiO4 thin films were as well discussed here. Fabricated by either sol-gel or radio frequency sputtering, annealed at various temperatures and characterized using photoluminescence spectroscopy. Essential physical and optoelectronic properties of the Mg2TiO4 luminance material as well as its optimal processing conditions were comprehensively reported.
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Yu, Bo-Syun, and 余柏勲. "Design and Model Free Predictive Current Control for Brushless Direct Current Motors with Low Rare Earth Material." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/5zc749.
Full textAbstract:
碩士國立臺灣海洋大學
系統工程暨造船學系
102
In operation, cogging torque of the motor generates torque ripple, further noise, vibration or shaking, etc. These problems not only affect motor’s performance and life, but also can be used in high-precision control of machinery. In order to solve problems of cogging torque, and improve the interaction of magnetic circuit in the motor. By the micro-structure, reduced the motor usage of rare earth material Through a simple parameter setting, complete the fast simulation analysis to understand the impact of micro-groove structure on the cogging torque. The controller use model free predictive current control(MFPCC) to drive BLDC motor. The MFPCC has insensitive to the motor parameters different form model base predictive current control. The current sampling once before change the switch state. It can avoid current surge when switching state. Application of the brushless DC motor drive will check the feasibility in computer. The tracking current capability by MFPCC compare to model base predictive current control(MBPCC). Completion of the drive control system simulation.
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"Properties of Cerium Containing Lead Free Solder." Doctoral diss., 2012. http://hdl.handle.net/2286/R.I.15802.
Full textAbstract:
abstract: With increasing concerns of the intrinsic toxicity of lead (Pb) in electronics, a series of tin (Sn) based alloys involving silver (Ag) and copper (Cu) have been proposed as replacements for Pb-Sn solder and widely accepted by industry. However, they have a higher melting point and often exhibit poorer damage tolerance than Pb-Sn alloys. Recently, a new class of alloys with trace amount of rare-earth (RE) elements has been discovered and investigated. In previous work from Prof. Chawla's group, it has been shown that cerium (Ce)-based Pb-free solder are less prone to oxidation and Sn whiskering, and exhibit desirable attributes of microstructural refinement and enhanced ductility relative to lanthanum (La)-based Sn-3.9Ag-0.7Cu (SAC) alloy. Although the formation of RESn3 was believed to be directly responsible for the enhanced ductility in RE-containing SAC solder by allowing microscopic voids to nucleate throughout the solder volume, this cavitation-based mechanism needs to be validated experimentally and numerically. Additionally, since the previous study has exhibited the realistic feasibility of Ce-based SAC lead-free solder alloy as a replacement to conventional SAC alloys, in this study, the proposed objective focuses on the in in-depth understanding of mechanism of enhanced ductility in Ce-based SAC alloy and possible issues associated with integration of this new class of solder into electronic industry, including: (a) study of long-term thermal and mechanical stability on industrial metallization, (b) examine the role of solder volume and wetting behavior of the new solder, relative to Sn-3.9Ag-0.7Cu alloys, (c) conduct experiments of new solder alloys in the form of mechanical shock and electromigration. The research of this new class alloys will be conducted in industrially relevant conditions, and the results would serve as the first step toward integration of these new, next generation solders into the industry.Dissertation/Thesis
Ph.D. Materials Science and Engineering 2012
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Mix, Torsten. "Die L10-Struktur in Mn-Ga- und Mn-Al-Ga-Legierungen: magnetische Eigenschaften und Phasenumwandlungen." Doctoral thesis, 2018. https://tud.qucosa.de/id/qucosa%3A31848.
Full textAbstract:
Im binären Mn-Ga-System wurde für Legierungen mit 55 at.% bis 65 at.% Mangan die Phasenbildung der L10-Phase mit Röntgenbeugung und Differenzialkalorimetrie untersucht. Nach der Herstellung der L10-Phase in allen Legierungen erfolgte eine Untersuchung der intrinsischen magnetischen Eigenschaften. Die Mn55Ga45-Legierung zeigte dabei die höchste Sättigungsmagnetisierung mit µ0Ms = 0,81 T. Für diese Legierung erfolgten deshalb Versuche zur Verbesserung der extrinsischen Eigenschaften. Dazu wurden Pulver gemahlen und die Möglichkeit der Ausrichtung im Magnetfeld untersucht. Dabei konnte ein Texturgrad von 0,45 für Pulver mit einer Partikelgröße kleiner 10 µm erreicht und die Koerzitivfeldstärke um das 7-fache gegenüber der Volumenprobe erhöht werden. Weiterhin konnten die Pulverproben durch Heißkompaktieren bei 400 °C erneut zu
einer Volumenprobe gepresst werden. Die dabei erhaltene Probe besitzt eine Koerzitivfeldstärke von 0,16 T und eine leicht reduzierte Sättigungsmagnetisierung auf Grund einer Packungsdichte von 83 %.
Im ternären Mn-Al-Ga-System wurden Proben der Sollzusammensetzung Mn55Al45-xGax mit 5,625 < x < 22,5 hergestellt. Für Legierungen mit x >= 11,86 erwies sich eine Wärmebehandlung bei 600°C für 24 Stunden als ausreichend die reine L10-Phase zu erzeugen. Bei den Legierungen mit einem geringeren Ga-Anteil war eine zweistufige Wärmebehandlung notwendig, um ausschließlich L10 zu erhalten. Nach der ersten Wärmebehandlung bei 1100 °C entstand ein Phasengemisch aus gamma2 und L10(epsilon). Letzteres wurde aus der epsilon-Hochtemperaturphase gebildet. Durch die anschließende Wärmebehandlung bei 500 °C für 24 Stunden konnte die verbleibende gamma2-Phase in L10(gamma2) umgewandelt werden. Untersuchungen der lokalen Legierungszusammensetzung ergaben einen geringeren Mn-Anteil der L10(gamma2)-Phase im Vergleich zu L10(epsilon). Die Unterschiede in den zwei L10-Phasen konnten weiterhin durch eine Reflexaufspaltung in den Röntgenbeugungsaufnahmen sowie der Existenz zweier Curie-Temperaturen bestätigt werden. Die gemessenen Sättigungsmagnetisierungen ergaben eine Superposition beider Phasen und einen maximalen Wert von µ0Ms = 0,85 T. Untersuchungen der thermischen Stabilität der L10-Phasen bei 700 °C zeigten, dass die L10(gamma2)-Phase thermisch stabil ist und sich die L10(epsilon)-Phase langsam in beta-Mn und gamma2 zersetzt. Bei der Zersetzung war im Vergleich zum binären Mn-Al-System eine starke Steigerung der thermischen Stabilität durch die Substitution geringer Mengen Galliums zu erkennen. Über die zersetzungsbedingte Reduktion der Magnetisierung konnten Abschätzungen der Zersetzungskinetik getroffen werden.
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Bittner, Florian. "Untersuchung der Wechselwirkung von Verarbeitung, Gefüge und Eigenschaften hartmagnetischer Mn-Al-Legierungen mit L1 0-Struktur." Doctoral thesis, 2017. https://tud.qucosa.de/id/qucosa%3A30692.
Full textAbstract:
Die vorliegende Arbeit behandelt die Wechselwirkung von Verarbeitung und Gefüge Mn-Al basierter hartmagnetischer Werkstoffe sowie die Auswirkung des Gefüges auf deren Eigenschaften. Dabei wurde das Gefüge der metastabilen tau-Phase im Anschluss an die Phasenbildung aus der Hochtemperaturphase epsilon-MnAl und die Auswirkung einer anschließenden Umformung untersucht. Der Schwerpunkt der Arbeit lag in der Analyse der Evolution verschiedener Gefügebestandteile, wie Grenzflächenverteilung, Versetzungen und Korngröße unter Verwendung von Rasterelektronenmikroskopie und Elektronenrückstreubeugung.
Die epsilon-tau Umwandlung kann auf 2 verschiedene Routen erfolgen. In beiden Fällen wird die Bildung von 3 kristallographisch unterschiedlichen zwillingsähnlichen Defekten beobachtet, die als wahre Zwillinge, Ordnungszwillinge und Pseudozwillinge bezeichnet werden. Sie lassen sich als Rotationen um einen kristallographischen {111}-Pol beschreiben. Der Anteil der Zwillingsdefekte nach der Umwandlung, aber auch die Korngröße und Versetzungsdichte sind von der gewählten Umwandlungsroute abhängig. Während die Sättigungspolarisation annähernd gleich ist, reagiert die Koerzitivfeldstärke sensitiv auf den Gefügezustand. Eine niedrige Korngröße und hohe Versetzungsdichte tragen zu ihrer Erhöhung bei.
Eine anschließende Kaltumformung erzeugt ein vielfach verzwillingtes Verformungsgefüge mit hoher Koerzitivfeldstärke. Wärmebehandlungen und die Analyse der Schärfe von Kikuchi-Beugungsbildern haben gezeigt, dass nicht die hohe Zwillingsdichte, sondern primär Versetzungen im Verformungsgefüge die Koerzitivfeldstärke steigern. Warmumformung von tau-MnAl führt zur dynamischen Rekristallisation. Die Kinetik der Gefügeneubildung und die resultierende Korngröße sind stark von der Umformtemperatur abhängig. Durch Umformung lässt sich eine kristallographische Texturierung von tau-MnAl erreichen. Die Orientierung der magnetisch leichten [001]-Richtung ist dabei vom gewählten Umformverfahren und gegebenenfalls von der Nachbehandlung abhängig. Statische und dynamische Rekristallisation reduzieren den Anteil der Zwillingsdefekte signifikant und besonders Pseudozwillinge und Ordnungszwillinge werden im Gefüge beseitigt. Das Rekristallisationsgefüge weist gegenüber dem Umwandlungsgefüge einen geringeren Widerstand gegen die mit der Zersetzungsreaktion verbundene Bildung von beta-Mn auf. Die Ursache liegt in einer selektiven beta-Mn-Bildung an allgemeinen Korngrenzen, während die Zwillingsdefekte einen erhöhten Widerstand gegen sie Zersetzung aufweisen.