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1
Masood, Ansar. "Functional Metallic Glasses." Doctoral thesis, KTH, Teknisk materialfysik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-101901.
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For decades, Metallic Glass, with its isotropic featureless structure while exhibiting outstanding mechanical properties was possible only at a high rate of quenching and with at least one dimension in the submicron regime. This limitation was overcome with the discovery of Bulk Metallic glasses, BMGs, containing three or more elements following the additional two empirical rules of optimum geometric size differences and negative energy of mixing among the constituent elements. Since then thousands of Fe-, Ni-, Al-, Mg-, Ti- based BMGs have been discovered and comprehensively investigated mainly by groups in Japan and USA. Yet the discovery of new combinations of elements for BMGs is alchemy. We do not know with certainty which element when added will make possible a transition from being a ribbon to a bulk rod. In this thesis we report a discovery of castable BMGs rods on substitution of Fe by nickel in an alloy of FeBNb which could otherwise have been only melt-spun into ribbons. For example, we find that substitution of just 6 at.% of Fe raises the glass forming range, GFA, to as much as ∆Tx =40K while the other parameters for GFA like Trg, γ, and δ reach enhanced values 0.57, 0.38, and 1.40 respectively. Furthermore, the electrical conductivity is found to increase by almost a factor of two. Magnetically it becomes softer with coercivity 260mOe which further reduces to much lower values on stress relaxation. Ni does not seem to carry a magnetic moment while it enhances the magnetic transition temperature linearly with Ni concentration. We have investigated the role of Ni in another more stable BMGs based FeBNbY system in which case ∆Tx becomes as large as 94K with comparable enhancement in the other GFA parameters. Due to the exceptional soft magnetic properties, Fe-based bulk metallic glasses are considered potential candidate for their use in energy transferring devices. Thus the effect of Ni substitution on bulk forming ability, magnetic and electrical transport properties have been studied for FeBNb and FeBNbY alloy systems. The role of Ni in these systems is densification of the atomic structure and its consequence. We have exploited the superior mechanical properties of BMGs by fabricating structures that are thin and sustainable. We have therefore investigated studies on the thin films of these materials retaining their excellent mechanical properties. Magnetic properties of FeBNb alloy were investigated in thin films form (~200-400nm) in the temperature range of 5-300K. These Pulsed Laser deposited amorphous films exhibit soft magnetism at room temperature, a characteristic of amorphous metals, while they reveal a shift in hysteresis loop (exchange anisotropy, HEB=18-25Oe), at liquid helium temperature. When thickness of films is reduced to few nanometers (~8-11nm), they exhibit high transparency (>60%) in optical spectrum and show appreciably high saturation Faraday rotation (12o/μm, λ= 611nm). Thin films (~200-400nm) of Ni substituted alloy (FeNiBNb) reveal spontaneous perpendicular magnetization at room temperature. Spin-reorientation transition was observed as a function of film thickness (25-400nm) and temperature (200-300K), and correlated to the order/disorder of ferromagnetic amorphous matrix as a function of temperature. These two phase films exhibits increased value of coercivity, magnetic hardening, below 25K and attributed to the spin glass state of the system. Using the bulk and thin films we have developed prototypes of sensors, current meters and such simple devices although not discussed in this Thesis. Ti-based bulk metallic glasses have been attracting significant attention due to their lower density and high specific strength from structural application point of view. High mechanical strength, lower values of young’s modulus, high yield strength along with excellent chemical behaviors of toxic free (Ni, Al, Be) Ti-based glassy metals make them attractive for biomedical applications. In the present work, toxic free Ti-Zr-Cu-Pd-Sn alloys were studied to optimize their bulk forming ability and we successfully developed glassy rods of at least 14mm diameter by Cu-mold casting. Along with high glass forming ability, as-casted BMGs exhibit excellent plasticity. One of the studied alloy (Ti41.5Zr10Cu35Pd11Sn2.5) exhibits distinct plasticity under uniaxial compression tests (12.63%) with strain hardening before failure which is not commonly seen in monolithic bulk metallic glasses.QC 20120906
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Sheard, Simon M. "Metallic glasses for pulse compression." Thesis, University of Bath, 1989. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.328680.
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Veligatla, Medha. "Glass Forming Ability, Magnetic Properties, and Mechanical Behavior of Iron-Based and Cobalt-Based Metallic Glasses." Thesis, University of North Texas, 2014. https://digital.library.unt.edu/ark:/67531/metadc699947/.
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Lack of crystalline order and microstructural features such as grain/grain-boundary in metallic glasses results in a suite of remarkable attributes including very high strength, close to theoretical elasticity, high corrosion and wear resistance, and soft magnetic properties. In particular, low coercivity and high permeability of iron and cobalt based metallic glass compositions could potentially lead to extensive commercial use as magnetic heads, transformer cores, circuits and magnetic shields. In the current study, few metallic glass compositions were synthesized by systematically varying the iron and cobalt content. Thermal analysis was done and included the measurement of glass transition temperature, crystallization temperature, and the enthalpies of relaxation and crystallization. Magnetic properties of the alloys were determined including saturation magnetization, coercivity, and Curie temperature. The coercivity was found to decrease and the saturation magnetization was found to increase with the increase in iron content. The trend in thermal stability, thermodynamic properties, and magnetic properties was explained by atomic interactions between the ferromagnetic metals and the metalloids atoms in the amorphous alloys. Mechanical behavior of iron based metallic glasses was evaluated in bulk form as well as in the form of coatings. Iron based amorphous powder was subjected to high power mechanical milling and the structural changes were evaluated as a function of time. Using iron-based amorphous powder precursor, a uniform composite coating was achieved through microwave processing. The hardness, modulus, and wear behavior of the alloys were evaluated using nano-indentation.
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Stoica, Mihai. "Casting and characterization of Fe-(Cr,Mo,Ga)-(P,C,B) soft magnetic bulk metallic glasses." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2005. http://nbn-resolving.de/urn:nbn:de:swb:14-1134119175311-08460.
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The ferromagnetic bulk metallic glasses (BMGs) started to be investigated only in the last 10 years.They are difficult to cast, but their properties are uniques. The work deals with casting, mechanical and soft magnetic properties of new Fe-based BMGs. Such alloys can be cast directly in samples with various geometries and they can be use as magnetic parts in different devices.
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Hostert, Carolin [Verfasser]. "Towards designing elastic and magnetic properties of Co-based thin film metallic glasses / Carolin Hildegard Hostert." Aachen : Hochschulbibliothek der Rheinisch-Westfälischen Technischen Hochschule Aachen, 2012. http://d-nb.info/1026067758/34.
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Mastrogiacomo, Giovanni. "Development of Fe-based metallic glasses via destabilization of the solid state and characterization of their magnetic and electrical properties /." Zürich : ETH, 2008. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=17634.
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Shah, Zulfiqar Hussain. "Synthesis and Characterizations of Fe-based Metallic Glassy Systems." Thesis, KTH, Materialvetenskap, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-37395.
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This thesis is a study of tailoring amorphous Fe-B-Si based alloy to produce bulk glassy rods by adding Nb. We have prepared rapid quenched thin ribbons (thickness ~12 µm) by melt spinning, and glassy rods of diameter ~1mm by Cu-mold casting based on compositions (Fe0.78B0.13Si0.9)100-xNbx (x=0, 4, 8, 12), and studied their different physical properties. The melt-spun ribbons are found to be X-ray amorphous, whereas some nano-crystallinity is observed in the case of rods. All the ribbons show high saturation magnetization and low coercivity, which are the desirable characteristics of a soft ferromagnet. These ribbons are thus suitable for designing high frequency transformers, and sensors from an applications point of view. With increasing Nb content their saturation magnetization, ferromagnetic Curie temperature, and resistivity are found to decrease as expected. The temperature dependence of electrical resistivity shows small positive temperature co-efficient that is expected for a metallic disordered material. We have also studied the modification of the properties on thermal annealing the (Fe0.78B0.13Si0.9)96 Nb4 ribbon at different temperatures in a neutral atmosphere.
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Rojananan, Siriporn. "Formation and properties of ferromagnetic bulk metallic glasses." Thesis, University of Sheffield, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.401124.
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Laws, Kevin J. Materials Science & Engineering Faculty of Science UNSW. "The production and properties of lightweight bulk metallic glasses." Awarded by:University of New South Wales. Materials Science & Engineering, 2007. http://handle.unsw.edu.au/1959.4/40462.
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An inverted die casting technique has been developed for the rapid and reproducible production of high quality lightweight bulk metallic glass (BMG) castings. Comprehensive processing maps for producing lightweight BMG samples of cross section 3.15 mm x 7 mm and a length of 125 mm were developed as a means of identifying the optimum casting conditions for producing casting of high structural integrity, maximum length and enhanced surface quality. Utilising these maps, Mg65CU25Y10 and Ca65Mg15Zn20 BMGs were consistently produced using the inverted injection die casting method and a naturally cooled copper mould, by choosing injection parameters that stabilise the molten metal flow front within the mould cavity. Highest quality Mg65CU25Y10 BMG bars were produced in the casting temperature range of 560 C to 580 C and gate velocities in the range of 12.5 to 15 m/s. Highest quality Ca65Mg15Zn20 BMG bars were produced in the casting temperature range of 480 C to 520 C and gate velocities in the range of 13.8 to 14.7 m/s. The casting parameter range for achieving the highest quality castings for the lightweight BMGs examined was found to be practically identical and related to the casting system geometry. The use of higher holding pressures when casting was also found to increase the sample surface quality due to a post-casting consolidation process during sample cooling. As part of the experimental program, critical cooling rate experiments were carried out, whereby the change in casting temperature over time was measured between Tl and Tg. The resulting castings were analysed using x-ray diffraction (XRD). The Mg65CU25Y10 BMG was found to have a critical cooling rate between 49 and 61 C/sec, and may be gravity cast in a copper mould to achieve a completely amorphous structure between 3 and 3.75 mm, or readily cast using the inverted injection method successfully to obtain a thickness of 3.15 mm. The Ca65Mg15Zn20 BMG was found to have a critical cooling rate between 150 and 170 C/sec, and may be cast using the inverted injection method to achieve a completely amorphous structure of a diameter 8 to 9 mm. From the as-cast samples, differential scanning calorimetry (DSC) experiments were carried out as to determine the thermal properties of both materials where it was found that the Mg65CU25Y10 BMG had glass transition and crystallisation temperatures that varied with heating rate. Tg varied from 138 C for a heating rate of 2 C/min to 148 C for a heating rate of 20C/min. Tx varied from 195 C for a heating rate of 2C/min to 213 C for a heating rate of 20C/min. This indicates a supercooled liquid (SCL) interval of 57 to 65 C. The Ca65Mg15Zn20 BMG was found to have glass transition and crystallisation temperatures that were almost independent of heating rate. Tg varied from 102 C for a heating rate of 5 C/min to 105 C for a heating rate of 20 C/min. Tx remained relatively unchanged with heating rate at 137 C, indicating a SCL interval of 32C. Isothermal DSC results show that the onset of crystallisation occurs much more quickly in the Ca65Mg15Zn20 BMG and follows a non-Arrhenius type relationship as opposed to the slower, Arrhenius crystallisation kinetics displayed by the Mg65CU25Y10 BMG. In conjunction with this work, the elevated temperature mechanical properties of these BMGs was studied. When deformed in tension at an elevated temperature under constant strain rate conditions, it was found that an increase in test temperature resulted in a decrease in both peak stress and flow stress. It was also found that an increase in strain rate resulted in an increase in both peak stress and flow stress. It was established that Newtonian flow occurred at high temperatures in the SCL region and at lower strain rates. The Ca65Mg15Zn20 BMG was found to be far more strain rate sensitive with respect to brittle fracture, exhibiting a maximum achievable strain rate for homogeneous flow of 10 -3/S compared to 10 -1/S for the Mg65CU25Y10 BMG. Elongations achieved for the Mg65CU25Y10 BMG exceeded 1300% compared to a maximum elongation of 598% for the Ca65Mg15Zn20 BMG under constant temperature/ constant strain rate conditions, with elongation usually limited due to the onset of crystallisation. Both BMGs were found to crystallise under certain deformation conditions. For these conditions, the Mg-based BMG was found to display a stress increase due to crystallisation prior to the times determined by static crystallisation experiments due to dynamic segregation of the amorphous phase into Cu rich and Y rich regions, as determined by atom probe tomography (APT). Where crystallisation occurred in the Ca-based BMG under dynamic conditions a delayed stress increase due to crystallisation was observed in comparison to static crystallisation experiments. The dynamic stabilisation (time delay to crystallisation) of the amorphous phase in the Ca65Mg15Zn20 alloy was found to decrease with increasing test temperature and decreasing strain rate. Constant load defomation experiments were carried out at a constant heating rate of 5 C/sec for the Ca65Mg15Zn20 BMG. It was found that stress overshoot behaviour was avoided and a strain of 850% was achieved prior to crystallisation hardening and subsequent failure which is larger than that observed in constant strain rate testing.
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Denis, Pierre [Verfasser]. "Nanostructured metallic glasses : structure, properties and applications / Pierre Denis." Ulm : Universität Ulm, 2020. http://d-nb.info/1212936299/34.
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Ramasamy, Parthiban. "Soft Ferromagnetic Bulk Metallic Glasses with Enhanced Mechanical Properties." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2018. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-232112.
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Fe-based bulk metallic glasses (BMGs) have gained considerable interest due to their excellent soft magnetic properties with high saturation magnetization, high electrical resistivity, very good corrosion resistance, low materials cost, extremely high mechanical strength and hardness. In spite of having excellent strength, Fe-based BMGs are not used as structural materials in service, so far. The major obstacle is their inherent brittleness under mechanical loading, once a crack is developed the material fails catastrophically. Owing to the ever growing industrial demand for the materials with outstanding properties, aside from exploring new alloy compositions, it is pertinent to understand why or why-not the existing system work and how to improve their properties. Recent reports suggested that the plastic deformability can be enhanced by introducing different microstructural heterogeneities such as free volume enhanced regions, separated phases, nano-crystals, atomic clusters caused by for instance additions of small amount of soft elements. Understanding the effect of addition of soft elements to Fe-based BMGs on thermal stability, structural evolution, magnetic and mechanical properties are the main point which this work addresses.
In this work, a study on two different soft ferromagnetic Fe-based glass forming alloys are presented, both of them known to have very high mechanical strength and excellent soft magnetic properties but so far have not been used in any industrial applications. The important issue is with the brittle behavior of this BMGs, particularly under mechanical loading. In each glass forming alloys, the aim was to find out the optimum quantity of the soft elements (Cu and Ga), which can be added to improve their room temperature plastic deformability without affecting the glass forming ability (GFA) and soft magnetic properties.
The first glass forming alloy that is studied is Fe36Co36B19.2Si4.8Nb4. This glass forming alloy is highly sensitive to the impurities, only pure elements were used to form this alloy. The addition of only 0.5 at.% Cu completely changes the thermal stability and structural evolution but it also improves the mechanical properties. In case of Ga addition up to 1.5 at.% the crystallization behavior remains unaltered and the thermal stability improves marginally. The addition of Ga improves the plastic deformability of the glass by forming soft zones, whose melting point is much lower compared to rest of the alloy. These soft zones are responsible for the plastic deformation of this glass. Thus addition of Ga is very beneficial in improving the mechanical properties of this Fe-based BMG.
In the second part, Fe74Mo4P10C7.5B2.5Si2 glass forming alloy is studied. Unlike the aforementioned alloy, this glass forming alloy is not very sensitive to the impurities, industrial grade alloy elements can also be used to form this alloy. In this alloy addition of Cu is beneficial only up to 0.5 at.%, beyond that Cu addition deteriorates GFA and magnetic properties. In case of Ga addition up to 2 at.% the crystallization behavior remains unaltered and the thermal stability improves marginally. Similar to the FeCoBSiNb glass, the addition of Ga in FeMoPCBSi glass also improves the plastic deformability of the glass by formation of soft zones.
Addition of small at.% Ga proved be an viable solution to improve the plastic deformability in the ferromagnetic Fe-based metallic glasses without compromising on thermal and magnetic properties of the glass.
In the final part we tried to cast the Fe74Mo4P10C7.5B2.5Si2 glass in a complex shape using an industrial high pressure die casting (HPDC) set up. The important issues were with the casting alloy temperature, casting speed and die material. The aim of our work was to optimize the die material suitable for casting the BMGs and then address the issues with casting temperature and casting speed. We have thus attempted to gain a basic knowledge in casting the Fe-based BMG in industrial scale. Our effort was tremendously successful, we were able to produce fully amorphous complex shaped samples with excellent surface finish. We have thus made a considerable advancement towards understanding the basics behind improving the room temperature plastic deformability in Fe36Co36B19.2Si4.8Nb4 and Fe74Mo4P10C7.5B2.5Si2 ferromagnetic BMGs. We have also made a considerable progress in industrialization of bulk ferromagnetic BMGs.
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Sabet-Sharghi, Riaz. "Composition dependence of mechanical properties in Al-rich metallic glasses." Thesis, McGill University, 1993. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=26134.
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The effect of composition on the mechanical properties of high Al content Al-Y-Ni metallic glasses has been studied. Nine samples in all were prepared with a composition of ${ rm Al sb{85}Y} sb{x}{ rm Ni} sb{15-x}({ rm x}=3, ...,11).$ The amorphous alloys were first tested using both XRD and DSC. The DSC runs revealed that the samples were made up of two different types: one showing no glass transition and a lower crystallization temperature, and the other showing a distinct glass transition with a higher crystallization temperature indicating that they are truly homogeneous glasses. The samples showed a Young's modulus that does not seem to reveal any distinct compositional dependence whereas, the tensile strengths showed a distinct decreasing trend with increasing Y content. Values of various mechanical properties and crystallization temperatures obtained in this study are compared to those reported by other groups. We find very high specific strengths in these glasses, which combined with their excellent ductility makes them ideal structural materials. The effect of annealing is also examined and it is found that the samples lose a large proportion of their tensile strength and ductility when annealed.
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Albertos, Fernando. "Study of the catalytic properties of iron based metallic glasses." Thesis, University of Cambridge, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.276851.
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Alper, Muersel. "Electrodeposited magnetic superlattices : (growth, characterization, magnetic and magnetotransport properties)." Thesis, University of Bristol, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.261317.
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Lambrick, David Brynne. "Magnetic properties of metallic fine particle systems." Thesis, Durham University, 1986. http://etheses.dur.ac.uk/7087/.
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A study of the magnetic properties of metallic fine particle systems in the form of magnetic fluids has been made. The fluids were prepared utilising the organometallic decomposition route (detailed separately by N. Mason, Ph.D. thesis, Durham University 1986) and single metal systems containing Fe, Co and Ni were prepared from new precursors. The properties of the first hydrocarbon based mixed metal particle systems are also reported. For systems prepared with Fe precursors it is thought that the fine particles are not in the α-Fe phase but may be amorphous and/or consist of iron carbides. Co and Ni systems result in particles with bulk-metal like structures although Co usually forms in the f.c.c. phase. The h.c.p. is also observed. The mixed metal systems were of FeCo and Ni(_3)Fe and a tendency to form the superlattice or ordered structures was observed. In both cases Fe has been lost to the particles and this is thought to be due to the formation of volatile iron compounds during preparation and/or surfactant complexes. Narrow size distributions have been obtained in all cases with mean particle diameters in the range 4-10 nm and standard deviations of between 0.8 and 1.9. The form of the size distribution has been found to be Gaussian. A study of the anisotropy of the particles using torque and magnetisation measurements has found uniaxial anisotropy with the first anisotropy constant of the order lO(^5)Jmֿ(^3).The values observed are too large to be ascribed solely to shape anisotropy. Low temperature magnetisation measurements have revealed the existence of a paramagnetic component in the fluids. Loss of magnetisation has occurred in all systems and is thought to be due to oxidation of the metal.
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Ul-Haq, I. "Magnetic and transport properties of canonical spin glasses." Thesis, University of Salford, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.381742.
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Duarte, Correa María Jazmín. "Characterization of the structure, stability, mechanical and electrochemical properties of metallic glasses." Doctoral thesis, Universitat Politècnica de Catalunya, 2013. http://hdl.handle.net/10803/117789.
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Metallic glasses are often referred as glassy or amorphous alloys. They lack long-range order and microstructural defects that are characteristics in crystals, such as grain and phase boundaries and dislocations. These new materials have demonstrated very interesting structural and mechanical properties derived from their homogeneity in composition and the absence of grain boundaries. Structural, mechanical or chemical properties, among others, may be even superior to those observed in conventional metallic alloys, and therefore attracted great scientific and technological interest.
In this thesis project three different families of metallic glasses were selected to achieve a better understanding of amorphous alloys. First, a Ce-based alloy has been used to analyze a polyamorphic transition upon application of pressure to a more densely packed structure. X-ray diffraction and inelastic x-ray scattering data show a polyamorphic transition in the 2-10 GPa range, and this transition presents a hysteresis cycle between both compression and decompression data. The effect of this transition on mechanical properties is then evaluated. Second, a family of Fe-based metallic glasses, or amorphous steels, was selected to study their mechanical and electrochemical properties as a function of the structure and composition. The composition of the base alloy was first modified by addition of Yttrium in different concentrations as microalloying element and the structure was changed by thermal annealing, forming intermediate crystal/amorphous composites, up to a complete crystallization state. Finally, an entirely new alloy for biocompatible purposes has been designed, synthesized, and characterized. The basic structural characterization of this new Zr-Ti based amorphous alloy shows that is possible to produce the amorphous state in an alloy that does not contain toxic or unhealthy elements.Los vidrios metálicos, comúnmente conocidos como aleaciones amorfas o vitrificadas, carecen de orden a largo alcance así como de defectos microestructurales comunes en los cristales, tales como dislocaciones o fronteras de grano y/o de fase. Esta nueva clase de materiales ha demostrado poseer propiedades muy interesantes derivadas de la ausencia de microestructura y la homogeneidad en su composición. Estas propiedades, estructurales, mecánicas y químicas, entre otras, pueden llegar a ser incluso superiores a las observadas en materiales convencionales, y por lo tanto los vidrios metálicos han atraído gran interés por parte de la comunidad científica así como de carácter tecnológico. En este proyecto de tesis se pretende obtener un mayor conocimiento sobre aleaciones metálicas amorfas, para lo cual se propusieron tres familias diferentes de vidrios metálicos. Primero, se utilizó una aleación de base Ce para analizar transiciones poliamórficas, entre un estado de baja densidad hacia una estructura densamente empaquetada, por efecto de la presión. Los resultados obtenidos por difracción de rayos X y dispersión inelástica de rayos X muestran una transición en un rango de presiones de 2 a 10 GPa presentando además histéresis con respecto a los datos obtenidos en compresión y descompresión. El efecto de dicha transición en las propiedades mecánicas de la aleación es también evaluado. En segundo lugar se eligió una familia de aleaciones de base Fe, conocidos también como aceros amorfos. Las propiedades mecánicas y electroquímicas en función de la estructura y la composición fueron evaluadas mediante la introducción de itrio como elemento microaleante y la modificación de la estructura por medio de tratamientos térmicos con la obtención de estructuras compuestas nanocristal-amorfo hasta una completa cristalización. Finalmente, se diseñó y sintetizó una aleación completamente nueva con el propósito de evaluar biocompatibilidad. La caracterización estructural básica de esta nueva aleación de base Zr-Ti sin elementos tóxicos y/o alergénicos muestra que es posible obtener aleaciones amorfas con las composiciones propuestas
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Im, Soohyun. "Correlating Structural Heterogeneity to Properties of Metallic Glasses Using 4-D STEM." The Ohio State University, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=osu1618865204994021.
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Liao, Lexiang. "Formation, crystallization and magnetic properties of Nd-Fe-B glasses." Thesis, McGill University, 1988. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=61667.
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Fornell, Beringues Jordina. "Metallic glasses and derived composite materials: a correlation between microstructure and mechanical properties." Doctoral thesis, Universitat Autònoma de Barcelona, 2012. http://hdl.handle.net/10803/96381.
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Des de principis dels anys seixanta, els materials coneguts com a vidres metàl·lics han estat objecte d’un gran número d’investigacions centrades principalment en la comprensió de la seva estructura i de les propietats tèrmiques, magnètiques i mecàniques. Tal com el seu nom indica, sent vidres no presenten ordenament atòmic a llarg abast donant lloc a la seva estructura amorfa. Aquesta falta d’ordre els confereix propietats i comportaments considerablement diferents respecte als aliatges cristal·lins. En el camp de les propietats mecàniques, els vidres metàl·lics es caracteritzen per posseir un alt límit elàstic que, juntament amb la possibilitat d’obtenir-los en forma màssica, ha obert un nou camp d’interès en la utilització d’aquests com a materials estructurals. No obstant, la deformació plàstica a temperatura ambient succeeix de forma molt localitzada mitjançant la formació de bandes de cisalla. Com a conseqüència, els vidres metàl·lics, enlloc d’experimentar enduriment per deformació típica dels materials cristal·lins, s’ablaneixen impedint una deformació plàstica estable. Com a resultat, malgrat el seu alt límit de fluència, els vidres metàl·lics tendeixen a fracturar-se després d’una deformació macroscòpica limitada, restringint d’aquesta manera la seva utilització en molts camps d’aplicació. Així doncs, en els darrers temps, la millora de la plasticitat d’aquest tipus de materials s’ha convertit en l’objecte de molts treballs d’investigació. Apart d’alguns casos puntuals on s’han trobat vidres metàl·lics amb plasticitat intrínseca, el concepte més explorat per tal d’evitar tal ruptura catastròfica ha estat la precipitació d’una segona fase. Vàries rutes han estat provades per obtenir aliatges amb matriu amorfa amb més ductilitat: afegir directament una fase reforçant al material fos, dissenyar una composició adequada que resulti en un material compost al solidificar-lo o precipitar la segona fase durant un tractament tèrmic o de deformació. Seguint una d’aquestes rutes, un aliatge heterogeni format, ja sigui per una fase cristal·lina micro- o nano-mètrica, una fase quasicristal·lina o fins i tot una segona fase amorfa integrada dins una matriu amorfa ha estat fabricat.
L’estudi desenvolupat al llarg d’aquesta Tesi es centra bàsicament en la millora de les propietats mecàniques dels vidres metàl·lics, donant especial èmfasi a la millora de la plasticitat, mitjançant algunes de les tècniques esmentades anteriorment. Principalment, s’han estudiat els canvis estructurals induïts per deformació, tractament tèrmic i afegint un nou element en diferents famílies de vidres metàl·lics i l’efecte de tals en les propietats mecàniques resultants.
Els canvis estructurals han estat caracteritzats per tècniques de calorimetria, difracció de raig-X i per microscòpia electrònica. Tot seguit, la influència d’aquests en el comportament mecànic dels vidres s’ha portat a terme mitjançant principalment tests de compressió i nanoindentació.
Els canvis mecànics i estructurals ocasionats per tractaments tèrmics en dues famílies de vidres metàl·lics (basats en Ti i en Fe) han estat estudiats. D’aquesta secció podríem concloure que bé si s’ha observat una bona millora en les propietats mecàniques (mòdul de Young, duresa, resistència al desgast,etc) quan el tractament tèrmic s’ha dut a terme al voltant de la temperatura de transició vítria (microstructura formada per nanocristalls dispersos en una matriu amorfa) la plasticitat continua sent limitada. Tot seguit, hem estudiat els canvis ocasionats per l’addició d’un element, Nb, en una composició inicialment amorfa. Hem pogut observar, com a mesura que introduïm Nb a l’aliatge format per Ti, Zr, Cu i Pd la capacitat de formació vítria va disminuint fins que per un percentatge de Nb del 4 % atòmic ens trobem amb un aliatge pràcticament cristal·lí. No obstant, en les composicions amb el 2% i el 3% de Nb, on s’observa una microstructura formada per petits cristalls integrats en una matriu amorfa, s’ha observat un increment notable (al voltant del 10%) en la plasticitat de l’aliatge. Aquesta Tesi també engloba un estudi detallat de la resposta de materials inicialment amorfs al ser sotmesos a diferents nivells de deformació plàstica. Tot i ser sotmesos a les mateixes condicions de deformació, en l’aliatge basat en titani es detecta ablaniment, mentre que en l’aliatge format principalment per zirconi s’observa enduriment. Els possibles efectes d’aquest comportament dissimilar són explicats en termes de volum lliure, cristal·lització i canvis en l’ordre a curt abast.Metallic glasses have been the subject of widespread research since the 1960's with significant progress in the understanding of their behaviour. They are amorphous metallic alloys; as the name suggests, being glasses, they do not possess long range order because of their amorphous nature; formed by metals, they are not transparent to light. As a result, they exhibit unique chemical, physical, mechanical and magnetic properties compared to conventional crystalline metallic alloys. In particular, their high yield strength together with the possibility of casting them into bulk form has triggered the interest in using them as structural materials. However, plastic deformation at room temperature occurs in a highly localized manner by the formation of a few shear bands. Instead of work hardening, metallic glasses soften upon deformation, which prevents stable plastic elongation. Once yielding has set in, most metallic glasses tend to fracture in a brittle manner, with almost total lack of plasticity, restricting their use in many applications. As expected, in the last decade, many works were focused on the circumvention of this limited plasticity. Apart from some specific cases where intrinsic plasticity was observed, precipitation of a second phase was found to be the most effective way to promote multiple shear band formation and obtain both, high strength and enhanced plasticity. Many methods were developed to achieve such heterogeneous microstructure. For instance, the second phase can be physically added to the alloy prior to casting, precipitated directly from the melt or by thermal or mechanical treatments of the as-cast alloy. Following one of those procedures a microstructure composed of either a micro- or nano- sized crystalline, quasi-crystalline or non-crystalline phases embedded in an amorphous matrix can be synthesized. The structural and mechanical changes induced in metallic glasses by annealing, element addition and deformation form the main topic of the work presented in this Thesis. The microstructural changes have been characterized by calorimetry, X-ray diffraction and electron microscopy. The influence of these changes on the mechanical behaviour of these glasses has been mainly investigated through compression tests and nanoindentation tests. Structural and mechanical changes upon annealing have been studied in two families of metallic glasses: a Ti40Zr10Cu38Pd12 alloy and a Fe36Co36B19.2Si4.8Nb4 alloy. Annealing treatments of these alloys around Tg, when disperse nanacrystallites are embedded in an amorphous matrix, results in enhanced mechanical properties. However, the former is believed to deteriorate plasticity due to structural relaxation of the amorphous structure. On the other hand, the appearance of tiny nanocrystals embedded in an amorphous matrix is found to be the responsible of the increase above 10% of plastic strain when 3 % of Nb is added to the amorphous Ti40Zr10Cu38Pd12 alloy. However, a brittle behaviour is observed if the Nb content is exceedingly high (4%). The structural and mechanical changes experienced by metallic glasses upon deformation treatments have also been subject of study in this thesis. While strain softening in the Ti40Zr25Ni8Cu9Be18 metallic glass alloy takes place as deformation proceeds (by means of compression test as well as during nanoindentation), in the Zr62Cu18Ni10Al10 BMG the opposite effect, strain hardening, is observed. The possible reasons of the observed dissimilar behaviour have been explained in terms of free volume, crystallization and changes in the short range order.
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Dong, Yue [Verfasser]. "Structure, mechanical properties and post-processing of nano-structured metallic glasses / Yue Dong." Ulm : Universität Ulm, 2021. http://d-nb.info/1228985103/34.
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Garrison, Seth Thomas. "Catalytic Properties and Mechanical Behavior of Metallic Glass Powders." Thesis, University of North Texas, 2017. https://digital.library.unt.edu/ark:/67531/metadc984273/.
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Lack of crystalline order and microstructural features such as grain/grain-boundary in metallic glasses results in a suite of remarkable attributes including very high strength, close to theoretical elasticity, high corrosion and wear resistance, and soft magnetic properties. By altering the morphology and tuning of composition, MGs may be transformed into high-performance catalytic materials. In this study, the catalytic properties of metallic glass powders were demonstrated in dissociating toxic organic chemicals such as AZO dye. BMG powders showed superior performance compared to state of the art crystalline iron because of their high catalytic activity, durability, and reusability. To enhance the catalytic properties, high energy mechanical milling was performed to increase the surface area and defect density. Iron-based bulk metallic glass (BMG) of composition Fe48Cr15Mo14Y2C15B6 was used because of its low cost and ability to make large surface area by high energy ball milling. AZO dye was degraded in less than 20 minutes for the 9 hours milled Fe-BMG. However, subsequent increase in ball milling time resulted in devitrification and loss of catalytic activity as measured using UV-Visible spectroscopy. Aluminum-based bulk metallic glass (Al-BMG) powder of composition Al82Fe3Ni8Y7 was synthesized by arc-melting the constituent elements followed by gas-atomization. The particle size and morphology were similar to Fe-BMG with a fully amorphous structure. A small percentage of transition metal constituents (Fe and Ni) in a mostly aluminum alloy showed high catalytic activity, with no toxic by-products and no change in surface characteristics. Al-alloy particles, being light-weight, were easily dispersed in aqueous medium and accelerated the redox reactions. The mechanism of dye dissociation was studied using Raman and Infrared (IR) spectroscopy. Breaking of -C-H- and - C-N- bonds of AZO dye was found to be the primary mechanism. Mechanical behavior of individual BMG particles was evaluated by in situ pico-indentation in a scanning electron microscope (SEM) to understand the fracture mechanisms. Catastrophic shear banding was found to be the primary fracture mode, which supported the observation of flake formation during high energy ball milling.
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G??n, B??lent Materials Science & Engineering Faculty of Science UNSW. "Crystallization behaviour and rheological properties of a Mg-Cu-Y bulk metallic glass." Awarded by:University of New South Wales. Materials Science & Engineering, 2008. http://handle.unsw.edu.au/1959.4/43352.
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A repetitive low-pressure die casting technique has been developed for casting high quality Mg6SCU2SY10 bulk metallic glass (BMG) samples. Using these as-cast samples, the thermal and mechanical behaviour of the BMG in the supercooled liquid (SCL) region was investigated principally by uniaxial tensile testing, differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Using the die casting facility, charge temperature, injection pressure and injection velocity were found to be important parameters for controlling the length, porosity and degree of crystallinity in the as-cast samples. A processing map was generated which showed that a melt temperature and casting pressure in the range 560-580°C and 0.4-0.5 bar, respectively, generated the highest quality samples. The static crystallization behaviour of the as-cast BMG was investigated in detail. It was found that the kinetics of both anisothermal and isothermal crystallization were adequately represented by a number of transformation models. Using the Johnson-Mehl-Avrami-Kolmogorov (JMAK) relation in conjunction with isothermal DSC, the Avrami exponent was found to vary from 2.2 to 2.5 with increasing annealing temperature which implies that, at high annealing temperatures, nucleation occurs at a constant rate accompanied by diffusion-controlled growth of spherical grains. A comparable Avrami exponent of 2.34 was also calculated by anisothermal DSC using the Ozawa method. The tensile flow behaviour of the BMG was investigated over a range of strain rates (10.3to 10.1S•1) and deformation temperatures (150 to 170 QC) in the SCL region using standardized tensile test samples. It was found that, the flow stress increased rapidly to a maximum value followed by a decrease to a very low steady-state value. In the SCL region, the relationship between peak flow stress, strain rate and absolute deformation temperature was described adequately by the classic Sellars-Tegart constitutive relationship. There was also a good correlation between the Zener-Hollomon parameter, Z, and the flow characteristics of the BMG such as the transition from Newtonian to non-Newtonian flow at Z>1 031 S•1 and optimum superplasticity for Z-values in the range 5 x 1030 to 5 x 1031 S•1 where tensile elongations in excess of 1400% were achieved.
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Zamani, Atieh. "Metallic Amorphous Thin Films and Heterostructures with Tunable Magnetic Properties." Doctoral thesis, Uppsala universitet, Materialfysik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-239950.
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The primary focus of this thesis is to study the effect of doping on magnetic properties in amorphous Fe100−xZrx alloys. Samples with compositions of x = 7,11.6 and 12 at.% were implanted with different concentrations of H. Moreover, the samples with a composition of x = 7 at.% were also implanted with He, B, C and N. Magnetic measurements were performed, using SQUID magnetometry and MOKE, in order to compare the as-grown and the implanted films. The Curie temperature (Tc) increases and the coercivity (Hc) decreases, with increasing dopant volume. We also found that Hc increases with temperature for B and C doped samples. Magnetization curves at low temperature validate the presence of non-collinear spin configurations in the as-grown films, which is suppressed after doping, resulting in films with tunable soft magnetic properties. We have also studied the effect of interlayer mixing and finite size effects on FeZr in Fe92Zr8/AlZr multilayer films, and found an anomalous increase of Tc with decreasing thickness. Strain induced changes in the magnetization of an amorphous Co95Zr5 film at the orthorhombic phase transition of the BaTiO3 substrate, was also studied. The results show that structural modifications of the substrate increases the stress and hence changes the magnetic anisotropy in the amorphous Co95Zr5 layer. Finally, the magnetization reversal of Co and CoX heterostructures, with X being Cr, Fe, Ni, Pd, Pt and Ru, has been studied. For this purpose a synthetic antiferromagnet structure, FM/NM/FM, was used, where FM is a ferromagnetic Co or CoX layer and NM is a nonmagnetic Ru spacer layer. The FM layers are coupled antiferromagnetically across the NM layer. For a range of FM layer thicknesses, the exchange stiffness parameter Aex and the interlayer coupling (JRKKY ) of the Co or CoX layers were obtained. This is done by fitting M(H) curves, measured by SQUID magnetometry, to a micromagnetic model. The alloying in CoX resulted in a decreasing Aex and also a reduced MS. The experimental results are in a good agreement with DFT calculations.
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Dean, Colin. "Micromagnetic calculations of the magnetic properties of thin metallic films." Thesis, University of Central Lancashire, 1993. http://clok.uclan.ac.uk/19941/.
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A micromagnetic model has been developed to simulate the magnetisation in a metallic thin film. This is achieved by energy minimisation techniques. The energy of each grain in the medium includes Zeeman, anisotropy, magnetostatic and exchange. The magnetostatic energy is incorporated by considering each grain as a point dipole and its a magnitude was obtained in collaboration with J.J. Miles. The exchange coupling is incorporated by utilising the phenomenological expression introduced by Zhu and Bertram. The model consists of one thousand grains on a hexagonal lattice with periodic boundary conditions applied. The model was initially used to compute hysteresis loops and these agreed with loops produced by other micromagnetic models. AC Erased states were obtained by a technique we have developed based on simulated annealing. This produced erased states which were of low energy and well correlated. The erased state was found to consist of vortices, which increased in size as the exchange coupling increased. The difficulty of obtaining zero magnetisation was also found to increase as the exchange coupling increased - a problem also found experimentally. The Al plot was calculated from a comparison with the computed remanence curves. The Al plot undergoes a change from being negative in the purely magnetostatic case to positive in the presence of strong exchange coupling. This change in the form of Al agrees with experimental investigations. Furthermore, the magnitude of the magnetostatic interaction was varied. It was shown that by keeping the exchange coupling constant and varying the magnetostatic interactions, it was possible to change the form of Al. Thus, it is the detailed balance of the exchange and magnetostatic interaction which is of importance. The model was then extended to simulate magnetic force microscopy (MFM). The ac erased, dc demagnetised and recording medium consisting of two oppositely magnetised bits have been scanned to produce MFM images. The image of the recording medium agrees with the experimental image. It is anticipated that the images which we have produced will enhance the understanding of experimental images.
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Lefebvre, Josianne. "Superconductivity in metallic glasses (FexNi1-xZr2): from transport and magnetization properties to vortex dynamics." Thesis, McGill University, 2008. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=21908.
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Properties of the superconducting state of the series of pseudo-binary metallic glasses FexNi1−xZr2 have been studied from electrical transport and magnetization measurements performed using a nearby 2-dimensional electron gas (2DEG) as a magnetic flux detector. This series of alloys offers a variety of enviable qualities for the systematic study of superconducting properties amid which lies the alleged constant amorphous structure of alloys with different stoichiometry imparted by the similar atomic volume of the Fe and Ni atoms, which permits the determination of the dependence of superconducting parameters on chemical composition uniquely by eliminating structure-dependent contributions. Such a study aims at verifying how superconductivity is affected by the presence of iron which is known to induce pair-breaking spin fluctuations. The temperature dependence of Bc1 and Bc2, and the Tc dependence on the iron content x in the alloys are determined and found to decrease with increasing x as expected from the increase of spin fluctuations. Unexpected findings are also revealed: For instance, fluctuations in magnetization and anomalous hysteresis loops at the Bc2 transition in alloys containing a large amount of Fe challenge the veracity of the assumption that the amorphous structure of the alloys FexNi1−xZr2 remains constant with x. These results even bring the first evidence for the existence of a structural transition at some x value. The absence of long-range order in amorphous alloys confers them weak vortex pinning character and makes the vortex state in the FexNi1−xZr2 alloys ideal for the study of correlated systems since the density of vortices and the driving force can be tuned externally such as to measure their effects on correlations. For these reasons, dynamic vortex phases in these alloys were also studied. In particular, the transverse dynamics of vortex phases are investigated from Hall resistance measurements; large features are observed whiLes propriétés supraconductrices des verres métalliques pseudo-binaire FexNi1−xZr2 sont étudiées à partir de mesures de transport électrique, ainsi qu'à partir de mesures d'aimantation prises en utilisant un gaz d'électrons bidimensionnel comme détecteur de champ magnétique. Cette série d'alliages démontre une variété de qualités enviables pour l'étude systématique de propriétés supraconductrices parmi lesquelles figure la présomption que la structure amorphe des alliages constante pour différente stoechiométries conférée par le volume atomique similaire des atomes de Fe et de Ni, qui permet la définition de la dépendance des paramètres supraconducteurs sur la composition chimique uniquement et élimine les dépendances structurelles. Cette étude a donc pour but the vérifier comment la supraconductivité est affectée par la présence de fer dans le matériel, ce qui est reconnue pour causer des fluctuations de spin et tend à briser les paires de Cooper. La dépendance en température de Bc1 et Bc2, et la dépendance de Tc sur la quantité de fer x dans les alliages sont déterminées et montrent une régression avec la croissance de x comme prévue due à l'augmentation des fluctuations de spin. Des résultats non attendus sont aussi révélés: Par example, des fluctuations dans l'aimantation et des boucles d'hystérèse anormales à la transition Bc2 dans les alliages contenant une grande quantité de fer mettent en doute la véracité de la supposition que la structure amorphe des alliages FexNi1−xZr2 reste constante. Ces résultats constituent même la première preuve de l'existence d'une transition de phase structurelle pour une certaine valeur de x. L'absence d'ordre à longue portée confère aux supraconducteurs amorphes leurs faibles propriétés d'ancrages des vortex, ce qui rend l'état mixte des alliages de FexNi1−xZr2 idéal pour l'étude de systèmes corrélés puisque la densité de vortex ainsi que la force s
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Mridha, Sanghita. "Structure Evolution and Nano-Mechanical Behavior of Bulk Metallic Glasses and Multi-Principal Element Alloys." Thesis, University of North Texas, 2017. https://digital.library.unt.edu/ark:/67531/metadc984260/.
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Bulk metallic glasses and multi-principal element alloys represent relatively new classes of multi-component engineering materials designed for satisfying multiple functionalities simultaneously. Correlating the microstructure with mechanical behavior (at the microstructural length-scales) in these materials is key to understanding their performance. In this study, the structure evolution and nano-mechanical behavior of these two classes of materials was investigated with the objective of fundamental scientific understanding of their properties. The structure evolution, high temperature nano-mechanical behavior, and creep of two Zr-based alloys was studied: Zr41.2Ti13.8Cu12.5Ni10.0Be22 (Vitreloy1) and Zr52.5Ti5Cu17.9Ni14.6All0 (Vitreloy105). Devitrification was found to proceed via the formation of a metastable icosahedral phase with five-fold symmetry. The deformation mechanism changes from inhomogeneous or serrated flow to homogenous flow near 0.9Tg, where Tg is the glass transition temperature. The creep activation energy for Vitreloy1 and Vitreloy105 were 144 kJ/mol and 125 kJ/mol, respectively in the range of room temperature to 0.75Tg. The apparent activation energy increased drastically to 192 kJ/mol for Vitreloy1 and 215 kJ/mol for Vitreloy105 in the range of 0.9Tg to Tg, indicating a change in creep mechanism. Structure evolution in catalytic amorphous alloys, Pt57.5Cu14.7Ni5.3P22.5 and Pd43Cu27Ni10P20, was studied using 3D atom probe tomography and elemental segregation between different phases and the interface characteristics were identified.
The structure evolution of three multi-principal element alloys were investigated namely CoCrNi, CoCrFeMnNi, and Al0.1CoCrFeNi. All three alloys formed a single-phase FCC structure in as-cast, cold worked and recrystallized state. No secondary phases precipitated after prolonged heat treatment or mechanical working. The multi-principal element alloys showed less strain gradient plasticity compared to pure metals like Ni during nano-indentation. This was attributed to the highly distorted lattice which resulted in lesser density of geometrically necessary dislocations (GNDs). Dislocation nucleation was studied by low load indentation along with the evaluation of activation volume and activation energy. This was done using a statistical approach of analyzing the "pop-in" load marking incipient plasticity. The strain rate sensitivity of nanocrystalline Al0.1CoCrFeNi alloy was determined by in situ compression of nano-pillars in a Pico-indenter. The nanocrystalline alloy demonstrated a yield strength of ~ 2.4 GPa, ten times greater than its coarse grained counterpart. The nanocrystalline alloy exhibited high strain rate sensitivity index of 0.043 and activation volume of 5b3 suggesting grain boundary dislocation nucleation.
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Mac, Mahon Colm. "Magnetic and magnetoelastic properties of cerium substituted rare earth transition metal glasses." Thesis, University of Hull, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.395506.
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Asano, H., N. Koduka, K. Imaeda, M. Sugiyama, and M. Matsui. "Magnetic and junction properties of half-metallic double-perovskite thin films." IEEE, 2005. http://hdl.handle.net/2237/6775.
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Parmar, Baljit Singh. "The preparation and properties of nanocrystalline soft magnetic materials." Thesis, University of Sheffield, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.284381.
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Hussin, Rosli Bin. "Nuclear magnetic resonance studies of some germanate and phosphate based glasses." Thesis, University of Warwick, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.310014.
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Laosiritaworn, Yongyut. "Modelling the magnetic properties of thin metallic films using Monte-Carlo simulation." Thesis, University of Warwick, 2002. http://wrap.warwick.ac.uk/73508/.
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In this thesis, Monte Carlo studies of the static critical behaviour of metallic magnetic thin-films are presented. The studies make use of a finite size scaling method designed for anisotropic shaped structures. This finite size scaling method is based on an assumption that a single correlation length is required to describe a thin-film close to its critical temperature and has lead to the derivation of formulae from which thin-film critical temperatures and exponents can be extracted. Monte Carlo simulations for Ising thin-films are carried out in order to verify the validity of the assumption and hence the formulae. Various algorithms and seed numbers for a random number generator are tested to minimise statistical errors. These studies also show the evolution from 2D to 3D-like behaviours as the films' thicknesses are increased. Critical temperatures and exponents are investigated for simple cubic (SC), body centred cubic (BCC) and face centred cubic (FCC) thin-films. Our Ising 2D and 3D results are also shown to give good agreement with previous Monte Carlo work. We then move on to study in a more realistic model of a magnetic thin-film in which the 'exchange parameters' and anisotropic constants are extracted from 'first principles' electronic structure calculations, and used in Monte Carlo simulations of a classical Heisenberg model. We model thin-films of Fe grown on a W(OOl) substrate which have been subjected to extensive experimental investigation. In line with the Mermin-Wagner theorem, we find a slow convergence for the magnetisation with the system size L in 2D which is consistent with expected absence of finite magnetisation in the finite temperatures in the thermodynamic limit. From the thin-film results in finite size systems, the magnetisation in the surface layers is weaker than those in the inner layers and a similar trend is found for the susceptibility. Slow magnetisation convergence with size is also observed for all thin-films (thickness varying from 2 to 8 layers). Because of this and the sensitivity to statistical errors, only critical temperatures and 'susceptibility critical exponents' can be extracted from the susceptibility functions. The results again show a crossover from 2D towards 3D-like behaviour. The critical temperatures are lower than those calculated from mean-field approximations and are in good agreement with experimental values where available. The differences in results between isotropic and anisotropic systems in which the anisotropic constants are very small in comparison to 'exchange interactions' are not significant.
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Stoica, Mihai [Verfasser]. "Casting and characterization of Fe-(Cr,Mo,Ga)-(P,C,B) soft magnetic bulk metallic glasses / Mihai Stoica." Aachen : Shaker, 2005. http://d-nb.info/1186588829/34.
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Wikberg, Magnus. "Fundamental Properties of Functional Magnetic Materials." Doctoral thesis, Uppsala universitet, Teknisk-naturvetenskapliga fakulteten, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-133257.
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Magnetic properties of powders, thin films and single crystals have been investigated using magnetometry methods. This thesis provides analysis and conclusions that are supported by the results obtained from spectroscopic and diffraction measurements as well as from theoretical calculations. First, the magnetic behavior of transition metal (TM) doped ZnO with respect to doping, growth conditions and post annealing has been studied. Our findings indicate that the magnetic behavior stems from small clusters or precipitates of the dopant, with ferromagnetic or antiferromagnetic interactions. At the lowest dopant concentrations, the estimated cluster sizes are too small for high resolution imaging. Still, the clusters may be sufficiently large to generate a finite spontaneous magnetization even at room temperature and could easily be misinterpreted as an intrinsic ferromagnetic state of the TM:ZnO compound. Second, influence of lattice strain on both magnetic moment and anisotropy has been investigated for epitaxial MnAs thin films grown on GaAs substrates. The obtained magnetic moments and anisotropy values are higher than for bulk MnAs. The enhanced values are caused by highly strained local areas that have a stronger dependence on the in-plane axis strain than out-of plane axis strain. Finally, spin glass behavior in Li-layered oxides, used for battery applications, and a double perovskite material has been investigated. For both Li(NiCoMn)O2 and (Sr,La)MnWO6, a mixed-valence of one of the transition metal ions creates competing ferromagnetic and antiferromagnetic interactions resulting in a low temperature three-dimensional (3D) spin glass state. Additionally, Li(NiCoMn)O2 with large cationic mixing exhibits a percolating ferrimagnetic spin order in the high temperature region and coexists with a two-dimensional (2D) frustrated spin state in the mid temperature region. This is one of the rare observations where a dimensional crossover from 2D to 3D spin frustration appears in a reentrant material.Felaktigt tryckt som Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 720
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Dawson, Samantha J. "Magnetic studies at low and intermediate temperatures." Thesis, University of Oxford, 1993. http://ora.ox.ac.uk/objects/uuid:7e78e494-1ed8-4020-9e59-44988ebf715b.
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This thesis contains three major areas of work. Chapter 1 describes the various film deposition techniques available for the growth of thin films. These different growth methods, substrate preparation and vacuum techniques, are discussed in the context of the effect of the growth process and deposition environment on film structure and quality. Chapter 2 describes the two film growth chambers. Chapter 3 describes the origin of giant magnetoresistance (GMR) in magnetic multilayered structures, and investigates the magnetoresistive properties of ion-beam sputtered CoCu multilayered thin films. Different film structures and deposition conditions have been investigated in order to maximise the size of negative magnetoresistance seen. Chapter 4 investigates the magnetic and giant magnetoresistive properties of sputtered CoCu and CoAg heterogenous alloys. The magnitude of the GMR effect is found to depend on the Co concentration and Co particle size. Chapter 5 describes an investigation of molecular beam epitaxy (m.b.e.) grown Dy/Y multilayer structures. The temperature dependences of helical magnetic structure in the Dy layers is investigated in two samples of different multilayer structures. Chapter 6 describes an acoustic interferometer which has been used to measure velocity and attenuation changes in an ultrasonic signal at frequencies of order IGHz. Also described is the production of the thin film piezoelectric transducers used in this technique, which are grown directly onto a single crystal of the material under investigation. The acoustic interferometer is used to investigate the dynamics of of a relaxation process between two time-reversed antiferromagnetic states in DyAlG, and a model for domain growth in this system is postulated. Chapter 7 investigates the phase diagram of DyPO4 using the acoustic interferometry technique. The observations of hysteresis effects are used to define a mixed phase region below the tricritical point.
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Abdi, Somayeh. "Investigation of new Ti-based metallic glasses with improved mechanical properties and corrosion resistance for implant applications." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-161213.
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The glass-forming Ti75Zr10Si15 alloy is regarded as a potential new material for implant applications due to its composition of non-toxic, biocompatible elements and many interesting mechanical properties. The effects of partial substitution of 15 at.-% Ti by Nb on the microstructure and mechanical behavior of the alloy have been investigated. The limited glass-forming ability (GFA) of the Ti75Zr10Si15 alloy results for melt-spun ribbons mainly in nanocomposite structures with β-type nanocrystals being embedded in a glassy matrix. Addition of Nb increases the glass-forming ability. Raising the overheating temperature of the melt prior to melt-spinning from 1923 K to 2053 K yields a higher amorphous phase fraction for both alloys. A decrease of hardness (H), ultimate stress and reduced Young’s modulus (Er) is observed for Ti60Zr10Nb15Si15 rods as compared to Ti75Zr10Si15 ones. This is attributed to an increase of the fraction of the β-type phase. The melt-spun ribbons show an interesting combination of very high hardness values (H) and moderate reduced elastic modulus values (Er). This results in comparatively very high H/Er ratios of >0.075 which suggests these new materials for applications demanding high wear resistance. The corrosion and passivation behavior of these alloys in their homogenized melt-spun states have been investigated in Ringer solution at 37°C in comparison to their cast multiphase crystalline counterparts and to cp-Ti and β-type Ti-40Nb. All tested materials showed very low corrosion rates. Electrochemical and surface analytical studies revealed a high stability of their passive states in a wide potential range. The addition of Nb does not only improve the glass-forming ability and the mechanical properties but also supports a high pitting resistance even at extreme anodic polarization. With regard to the corrosion properties, the Nb-containing nearly single-phase glassy alloy can compete with the β-type Ti-40Nb alloy. In addition, it has been demonstrated that thermal oxidation could be well applied to Ti75Zr10Si15 and Ti60Zr10Nb15Si15 melt-spun ribbons. Thermal oxidation treatment is one of the simple and cost-effective surface modification methods to improve the surface characteristics of these alloys. In the first tests, ribbon samples of the ternary and the quaternary alloy which were oxidized at 550°C in synthetic air showed suitable fundamental properties for implant applications, i.e. high hardness, good wettability and hydroxyapatite-forming ability after 10 days. All these properties recommend the new glass-forming alloys for application as wear- and corrosion-resistant coating materials for implantsDie glasbildende Legierung Ti75Zr10Si15 wird wegen ihrer biokompatiblen Zusammensetzung ohne toxische Elemente und auf Grund interessanter mechanischer Eigenschaften als potentielles neues Implantatmaterial betrachtet. Es wurden 15 at.-% Ti durch Nb partiell substituiert und die Effekte auf die Mikrostruktur und die mechanischen Eigenschaften der Legierung untersucht. Auf Grund der eingeschränkten Glasbildungsfähigkeit von Ti75Zr10Si15 bestehen die schmelzgeschleuderten Bänder dieser Legierung hauptsächlich aus Nanokomposit-Strukturen mit β-phasigen Nanokristallen in einer glasartigen Matrix. Die Zugabe von Nb steigert die Glasbildungsfähigkeit. Das Anheben der Überhitzungstemperatur der Schmelze vor dem Schmelzschleudern von 1923 auf 2053 K führt für beide Legierungen zu einem höheren Anteil amorpher Phase. Es wird bei der Legierung Ti60Zr10Nb15Si15 im Vergleich zur Ti75Zr10Si15-Legierung eine Abnahme der Härte (H), Bruchfestigkeit und ein reduzierter E-Modul (Er) beobachtet. Dies wird mit dem Anstieg des beta-Phasenanteils erklärt. Die schmelzgeschleuderten Bänder zeigen eine interessante Kombination aus sehr hoher Härte und moderaten E-Modul Werten (Er). Dies führt zu vergleichsweise sehr hohen H/Er-Verhältnissen von >0,075, wodurch diese Materialien für Anwendungen mit hohen Verschleißanforderungen geeignet sind. Das Korrosions- und Passivierungsverhalten dieser Legierungen in ihrem homogenisierten schmelzgeschleuderten Zustand wurde in Ringer-Lösung bei 37°C untersucht und mit dem gegossenen vielphasigen kristallinen Zustand dieser Legierungen sowie mit cpTi und beta-Typ Ti-40Nb verglichen. Alle untersuchten Materialien zeigten sehr niedrige Korrosionsraten. Elektrochemische Studien und Oberflächenanalysen belegen eine hohe Stabilität der Passivfilme in einem weiten Potentialbereich. Die Zugabe von Niob verbessert nicht nur die Glasbildungsfähigkeit und die mechanischen Eigenschaften, sondern erhöht weiterhin die Lochfraßbeständigkeit, selbst bei stark anodischer Polarisation. Bezüglich der Korrosionseigenschaften konkurriert die Nb-haltige fast einphasige glasartige Legierung mit β-phasigem Ti-40Nb. Weiterhin wurde gezeigt, dass an schmelzgeschleuderten Bändern der Legierung Ti75Zr10Si15 und Ti60Zr10Nb15Si15 eine thermische Oxidation erfolgreich durchgeführt werden konnte. Die thermische Oxidation ist eine der einfachsten und kosteneffektivsten Möglichkeiten der Oberflächenmodifikation um die Eigenschaften der Oberflächen dieser Legierungen zu verbessern. In den ersten Tests zeigten die Bänder-Proben der ternären und der quaternären Legierung, die bei 550°C in synthetischer Luft oxidiert wurden, entsprechende Eigenschaften für Implantat-Anwendungen, d.h. hohe Härte, gute Benetzbarkeit und die Fähigkeit nach 10 Tagen Hydroxylapatit auf der Oberfläche zu bilden. Alle zuvor genannten Eigenschaften machen diese neuen glasbildenden Legierungen zu geeigneten Materialien für die Anwendung als verschleiß- und korrosionsbeständige Beschichtung für Implantate
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Aykol, Muratahan. "Nano-scale Phase Separation And Glass Forming Ability Of Iron-boron Based Metallic Glasses." Master's thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/12609825/index.pdf.
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This study is pertinent to setting a connection between glass forming ability (GFA) and topology of Fe-B based metallic glasses by combining intimate investigations on spatial atomic arrangements conducted via solid computer simulations with experimentations on high GFA bulk metallic glasses. In order to construct a theoretical framework, the nano-scale phase separation encountered in metallic glasses is investigated for amorphous Fe80B20 and Fe83B17 alloys via Monte Carlo equilibration and reverse Monte Carlo simulation. The phenomenon is identified regarding three topological aspects: 1) Pure Fe-clusters as large as ~0.9 nm and Fe-contours with ~0.72 nm thickness, 2) Fe-rich highly deformed body centered cubic regions, 3) B-centered prismatic units with polytetrahedral order forming distinct regions of high and low coordinations are found. All topological aspects are compiled into a new model called Two-Dimensional Projection Model for predicting contributions to short and medium range order (MRO) and corresponding spacing relations. The outcome geometrically involves proportions approximating golden ratio. After successfully producing soft magnetic Fe-Co-Nb-B-Si based bulk metallic glass and bulk nanocrystalline alloys with a totally conventional route, influences of alloying elements on structural units and crystallization modes are identified by the developed model and radial distributions. While Co atoms substitute for Fe atoms, Nb and Si atoms deform trigonal prismatic units to provide local compactions at the outset of MRO. Cu atoms alter the type of MRO which resembles crystalline counterparts and accompanying nanocrystals that precipitate. The GFA can be described by a new parameter quantifying the MRO compaction, cited as Φ
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Lind, Mary Laura Johnson W. L. "Ultrasonic investigation of the elastic properties and liquid fragility of bulk metallic glasses in the supercooled liquid region /." Diss., Pasadena, Calif. : California Institute of Technology, 2008. http://resolver.caltech.edu/CaltechETD:etd-10262007-104725.
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Duman, Nagehan. "Magnetic Monitoring Approach To Kinetics Of Phase Transformations In Multicomponent Alloy Systems." Phd thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12614251/index.pdf.
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It is of great importance for a materials scientist both from fundamental and applicability aspects to have better understanding of solid-state phase transformations and its kinetics responsible for micro-/nano-structure development in alloys and corresponding physical and mechanical properties. Transformation kinetics can be analyzed by various experimental techniques such as thermal analysis, laborious electron microscopy combined with extensive image analysis or by measuring changes in electrical resistivity, specimen volume and relative intensities of diffraction lines caused by the phase transformation. Beyond these conventional techniques, this dissertation provides a novel magnetic monitoring approach to study the isothermal kinetics of phase transformations in multicomponent alloy systems involving measurable changes in overall magnetic moment as the transformation proceeds.
This dissertation focuses on understanding the microstructural evolution, macro- and micro-alloying behavior, magnetic properties, thermal characteristics, mechanical properties and kinetics of solid-state transformations, i.e. nanoscale precipitation and nanocrystallization, in nickel aluminides and Fe-based bulk amorphous alloys. Microstructural characterization of alloys was done by X-ray diffraction, scanning electron microscopy and transmission electron microcopy techniques. Magnetic properties were analyzed by vibrating sample magnetometry whereas thermal characteristics were evaluated by differential scanning calorimetry. Mechanical properties of alloys were determined by microhardness measurements and compression tests.
The influence of Fe macroalloying and 3d transition metal microalloying on the microstructure and properties of Ni-Al-Fe alloys were studied for as-cast and annealed states and it is shown that desired microstructure and related properties can be obtained by proper selection of the type and concentration of macro- or micro-alloying elements together with an appropriate annealing procedure. Thermomagnetic characterization reveals the nanoscale precipitation of a ferromagnetic second phase with annealing. In conjunction with saturation magnetization dependence on annealing, an optimum temperature is identified where nanoscale precipitates impart the highest extent of precipitation strengthening. The isothermal kinetics of ferromagnetic second phase precipitation reveals invariant Avrami exponents close to unity, indicating that nanoscale precipitation is governed by a diffusion-controlled growth process with decreasing growth rate, which closely resembles continuous precipitation kinetics.
Appropriate annealing of the Fe-based bulk amorphous alloy precursor produced by suction casting demonstrated extremely fine microstructures containing uniformly distributed and densely dispersed nanocrystals inside a residual amorphous matrix. In order to have better understanding of nanocrystallization mechanisms, kinetic parameters were determined via isothermal magnetic monitoring and non-isothermal differential scanning calorimetry where excellent agreement was obtained in Avrami exponent and activation energy. Analyzing the local kinetics, the nanocrystalline phase was found to evolve through distinct transformation regimes during annealing which were discussed on the basis of transformation kinetics theory and microscopical investigations on each characteristic transformation regime.
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Liao, Hao-Hsiang. "Thermal and thermoelectric properties of nanostructured materials and interfaces." Diss., Virginia Tech, 2012. http://hdl.handle.net/10919/19198.
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Many modern technologies are enabled by the use of thin films and/or nanostructured composite materials. For example, many thermoelectric devices, solar cells, power electronics, thermal barrier coatings, and hard disk drives contain nanostructured materials where the thermal conductivity of the material is a critical parameter for the device performance. At the nanoscale, the mean free path and wavelength of heat carriers may become comparable to or smaller than the size of a nanostructured material and/or device. For nanostructured materials made from semiconductors and insulators, the additional phonon scattering mechanisms associated with the high density of interfaces and boundaries introduces additional resistances that can significantly change the thermal conductivity of the material as compared to a macroscale counterpart. Thus, better understanding and control of nanoscale heat conduction in solids is important scientifically and for the engineering applications mentioned above.
In this dissertation, I discuss my work in two areas dealing with nanoscale thermal transport: (1) I describe my development and advancement of important thermal characterization tools for measurements of thermal and thermoelectric properties of a variety of materials from thin films to nanostructured bulk systems, and (2) I discuss my measurements on several materials systems done with these characterization tools.
First, I describe the development, assembly, and modification of a time-domain thermoreflectance (TDTR) system that we use to measure the thermal conductivity and the interface thermal conductance of a variety of samples including nanocrystalline alloys of Ni-Fe and Co-P, bulk metallic glasses, and other thin films. Next, a unique thermoelectric measurement system was designed and assembled for measurements of electrical resistivity and thermopower of thermoelectric materials in the temperature range of 20 to 350 °C. Finally, a commercial Anter Flashline 3000 thermal diffusivity measurement system is used to measure the thermal diffusivitiy and heat capacity of bulk materials at high temperatures. With regards to the specific experiments, I examine the thermal conductivity and interface thermal conductance of two different types of nanocrystalline metallic alloys of nickel-iron and cobalt-phosphorus. I find that the thermal conductivity of the nanocrystalline alloys is reduced by a factor of approximately two from the thermal conductivity measured on metallic alloys with larger grain sizes. With subsequent molecular dynamics simulations performed by a collaborator, and my own electrical conductivity measurements, we determine that this strong reduction in thermal conductivity is the result of increased electron scattering at the grain boundaries, and that the phonon component of the thermal conductivity is largely unchanged by the grain boundaries.
We also examine four complex bulk metallic glass (BMG) materials with compositions of Zr₅₀Cu₄₀Al₁₀, Cu46.25Zr44.25Al7.5Er₂, Fe₄₈Cr₁₅Mo₁₄C₁₅B₆Er₂, and Ti41.5Zr2.5Hf₅Cu42.5Ni7.5Si₁. From these measurements, I find that the addition of even a small percentage of heavy atoms (i.e. Hf and Er) into complex disordered BMG structures can create a significant reduction in the phonon thermal conductivity of these materials. This work also indicates that the addition of these heavy atoms does not disrupt electron transport to the degree with which thermal transport is reduced.Ph. D.
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Arvan, Behnaz [Verfasser], and Michael [Akademischer Betreuer] Farle. "Investigating magnetic and optical properties of hybrid magnetic-noble metallic nanowires synthesized by electrodeposition / Behnaz Arvan ; Betreuer: Michael Farle." Duisburg, 2017. http://d-nb.info/1133478867/34.
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Ramasamy, Parthiban [Verfasser], Jürgen [Akademischer Betreuer] Eckert, Jürgen [Gutachter] Eckert, and Livio [Gutachter] Battezzati. "Soft Ferromagnetic Bulk Metallic Glasses with Enhanced Mechanical Properties / Parthiban Ramasamy ; Gutachter: Jürgen Eckert, Livio Battezzati ; Betreuer: Jürgen Eckert." Dresden : Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2018. http://d-nb.info/1151127736/34.
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Evertz, Simon [Verfasser], Jochen M. [Akademischer Betreuer] Schneider, and Gerhard [Akademischer Betreuer] Dehm. "Quantum mechanically guided design of mechanical properties and topology of metallic glasses / Simon Evertz ; Jochen M. Schneider, Gerhard Dehm." Aachen : Universitätsbibliothek der RWTH Aachen, 2020. http://d-nb.info/1227992092/34.
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Jantan, Jaafar. "Magnetic phase transitions in Gd-rich metallic glasses." 1985. http://hdl.handle.net/2097/27461.
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Wang, Yu-Lin, and 王毓麟. "The Glass Forming Ability and Magnetic Properties of Fe–Nb–B–Ta Metallic Glasses." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/sy93j4.
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碩士國立臺北科技大學
材料科學與工程研究所
98
The effects of Ta addition on glass forming ability and soft magnetic properties of Fe-Nb-B metallic glass were investigated. The (Fe72Nb4B24)100-xTax (x = 0,1,2,3,4,5 and 6 at.%) ingots were arc-melted under argon atmosphere. A single roller melt-spinning method was employed to produce the alloy ribbons, and the copper mold injection casting was used to prepare 2mm alloy rods. The microstructures of alloy ribbons were shown to be amorphous when Ta additions ranged 0 and 4 at.%. Their ΔTx (= Tx-Tg) increased from 54.5 K (x = 0 at.%) to 70.7 K (x = 3 at.%) and subsequently decreased to 55.9 K (x = 5 at.%). Therefore, the values of ΔTx (= Tx-Tg), Trg (= Tg/Tm or Tg/Tl), γ, Rc, Zc, and Dmax was optimal with 3 at.% of Ta addition. The large ΔTx indicated that the Fe-Nb-B-Ta metallic glass had high glass forming ability and good thermal stability. The saturation magnetization (Ms) of Fe-Nb-B-Ta alloy ribbons decreased from 1.14 T to 0.64 T with increasing Ta from 0 at.% to 6 at.%, and the coercive force (Hc) decreased from 62.5 A/m to 13.2 A/m (x = 1 at.%) and then increased to 65.6 A/m (x=6 at.%). For alloy rods, the Ms decreased from 1.3 T to 0.9 T. Hc decreased from 3118 A/m to 2677 A/m (x = 1 at.%) and then increased to 5962 A/m (x = 6 at.%). Among the alloys investigated, (Fe72Nb4B24)99Ta1 demonstrated a combination of good glass forming ability and optimal soft magnetic properties in either ribbon or rod forms.
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Othman, Fauziah. "Random magnetic anisotropy effects in glasses based on Gd₆₅Co₃₅." 1985. http://hdl.handle.net/2097/27515.
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"Preparation of bulky ferromagnetic Fe₈₀P₁₃C₇ amorphous alloy." 2000. http://library.cuhk.edu.hk/record=b5890327.
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Chan Fu-wai = 非晶態鐵磁性鐵-磷-碳合金的製作 / 陳輔偉.Thesis (M.Phil.)--Chinese University of Hong Kong, 2000.
Includes bibliographical references.
Text in English; abstracts in English and Chinese.
Chan Fu-wai = Fei jing tai tie ci xing tie-lin-tan he jin de zhi zuo / Chen Fuwei.
Acknowledgments --- p.i
Abstract --- p.ii
Table of Content --- p.iv
Chapter Chapter 1: --- Introduction --- p.1
Chapter 1.1 --- Nucleation --- p.1
Chapter 1.1.1 --- Homogenous nucleation --- p.1
Chapter 1.1.2 --- Heterogeneous nucleation --- p.4
Chapter 1.2 --- The crystal growth --- p.5
Chapter 1.2.1 --- The solid-liquid interface --- p.5
Chapter 1.2.2 --- Lateral growth --- p.6
Chapter 1.2.3 --- Continuous growth --- p.6
Chapter 1.3 --- Non-equilibrium process --- p.8
Chapter 1.3.1 --- Reduction of impurities --- p.8
Chapter 1.3.2 --- Suppression of crystal growth --- p.8
Chapter 1.4 --- The change in metallurgy --- p.9
Chapter 1.4.1 --- The metallic glass --- p.9
Chapter 1.4.2 --- The properties of glass --- p.10
Chapter 1.4.3 --- The development of amorphous alloy --- p.11
Chapter 1.5 --- Preparation methods of amorphous alloy --- p.12
Chapter 1.6 --- The criterion of glass formation --- p.14
Chapter 1.7 --- The study of this project --- p.15
Reference --- p.16
Figure --- p.19
Chapter Chapter 2: --- Experiment --- p.36
Chapter 2.1 --- Preparation --- p.36
Chapter 2.2 --- Experimental procedure --- p.37
Chapter 2.3 --- Sample analysis --- p.38
Reference --- p.41
Figure --- p.42
Chapter Chapter 3: --- The formation of bulk ferromagnetic Fe-P-C amorphous alloy --- p.45
Abstract --- p.45
Introduction --- p.46
Experiment --- p.47
Result --- p.48
Reference --- p.49
Figure --- p.52
Chapter Chapter 4: --- Compaction of bulk ferromagnetic Fe-P-C amorphous alloy --- p.57
Abstract --- p.57
Introduction --- p.58
Experiment --- p.58
Result --- p.60
Reference --- p.61
Figure --- p.62
Chapter Chapter 5: --- Conclusion --- p.65
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Liu, Ming-Tsung, and 劉明聰. "Correlation between magnetic properties and the electronic structures of soft magnetic ternary Fe78-xYxB22 (x= 4-9) bulk metallic glasses." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/44746224478894499476.
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碩士淡江大學
物理學系碩士班
98
Fe and Y K-edge extended x-ray absorption fine structure (EXAFS), Fe (Y) L3,2-edge (L3-edge) x-ray absorption near-edge structure (XANES) and valence-band photoemission spectroscopy (VB-PES) measurements have been carried out to study soft magnetic ternary Fe78-xYxB22 bulk metallic glasses (BMGs). The combined XANES and VB-PES results do not show broadening of the Fe 3d band to support previous interpretation of the reduction of the magnetic moment in BMGs by Y-induced decrease of exchange splitting of Fe 3d orbitals. Instead, the density of delocalized/itinerant Fe 3d states in the vicinity of the Fermi level is found to be reduced by Y substitution, which reduces the strength of itinerant-states mediated ferromagnetic coupling between local spins on the Fe ions and the total magnetic moment of the Fe-based BMGs.
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Fang-WeiLin and 林芳緯. "Effect of B and Nb Elements on Magnetic and Heating Properties of Fe-based Bulk Metallic Glass." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/86995937645894700834.
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碩士國立成功大學
材料科學及工程學系碩博士班
101
Electromagnetic thermoablation is a new kind therapy for tumor. Soft magnetic bulk metallic glass is considered as a potential material for thermotherapy needle in electromagnetic thermoablation due to its high saturation magnetization (Ms), low coercivity (Hc) and high unusual eddy current loss. In this study Fe-B-Y-Nb alloys are selected as experimental materials of soft magnetic bulk metallic glass. The effect of Boron and Niobium content is investigated on the glass forming ability (GFA), magnetic property and heating ability in quaternary Fe-B-Y-Nb system. Fe-B-Y-Nb metallic glass was formed by Arc Melting. It was a function of B content in Fe68.4B28-XY4.6Nb4 (X=0, 1, 2, 3, 4) and Nb content in Fe66.5+YB25Y4.5Nb4-Y (Y=0, 0.5, 1, 1.5) alloys. The glass forming ability and thermal property were studied by differential scanning calorimetry (DSC). The phase and microstructure were characterized by X-ray diffractometer (XRD) ,SEM-BE imgage and electron backscatter diffraction (EBSD), respectively. In addition, the magnetic property were measured by Vibrating Sample Magnetometer (VSM). The experiment for heating ability was all under the condition with 5cm distance away from coil which applied alterative magnetic field. It is observed that Fe66.5B25Y4.5Nb4 alloy exhibits better GFA than other B content alloys with supercooled liquid region (Tx) 95. In Nb series alloys, Fe67B25Y4.5Nb3.5 alloy shows the best GFA in the study with Tx 97. According to hysteresis loop, Ms and Hc is 90.7 emu/g, 5.4 A/m for Fe66.5B25Y4.5Nb4 alloy, and 96.3 emu/g ,10.7 A/m for Fe67B25Y4.5Nb3.5 alloy. Owing to high Ms and low Hc, the heating ability can reach high temperature as Fe66.5B25Y4.5Nb4 alloy can reach 117oC and Fe67B25Y4.5Nb3.5 alloy can reach 132 oC. In the B series alloys, less NbBFe causes high Ms and narrow Hc. Therefore, B25 alloy exhibites better heating ability. In the Nb series alloys, NbBFe is suppressed to enhance Ms, but Y2O3 grew to broaden Hc by reducing Nb content. Due to ebb and rise of soft magnetic property with precipitation, Fe67B25Y4.5Nb3.5 exhibited the greatest heating ability in the study.
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Bracchi, Alberto. "Structural and Magnetic Properties of the Glass-Forming Alloy Nd60Fe30Al10." Doctoral thesis, 2004. http://hdl.handle.net/11858/00-1735-0000-000D-F262-0.
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