Dissertations / Theses on the topic 'Cu-based alloy'

The formation, structure and properties of bulk copper-based alloy glasses have been studied systematically. The production techniques employed included chill block melt produced as" cylindrical rods by casting into a stepped copper die having internal diameters raging between 0.5 and 4 mm and as conical bulk shapes, with a length of 50 mm and cone base diameters in the range 2-10 mm.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2012.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 39-40).
The Taylor method is a proven way to produce Cu-based shape memory microwires that aren't plagued by problems typical in polycrystalline copper SMAs produced by other methods. Here we set out to expand and refine this processing method to take the first critical steps toward large-scale continuous production. Using a semi-automated processing route, we draw continuous, uniform fibers up to 5 meters in length with diameters in the range 10 - 35 microns. Particular attention is paid to microwires made from a Cu-Sn shape memory alloy. In addition, because the properties of shape memory microwires depend on their diameter, processing parameters were varied to understand their impact on the diameters of the resulting wires.
by Eric Szablinski.
S.M.

The aim of this study is to synthesize and characterize new bulk amorphous alloys in the Ni- based systems. Theoretical studies on the basis of semi-empirical rules and the electronic theory of alloys in pseudopotential approximation has been provided in order to predict the impurity elements that will lead to an increase in the glass forming ability of Ni-based alloy systems. Glass forming ability of ten different compositions of alloys of Ni-Nb, Ni-Fe, Ni-B, Ni-Hf and Ni-Cr was simulated by using FORTRAN programs based on pseudopotential theory. In addition to the binary alloys, ternary alloys, which were formed by addition of 1 at% of third element to these systems, were also simulated. Since ordering energy is an indicator of glass forming ability, theoretical studies allowed to predict the effect of various third elements on the formation of amorphous phase. Furthermore, ordering energies were also used to calculate other parameters important for glass forming ability. In the second part of the study, on the basis of theoretical results, a series of casting experiments were done. Different compositions of Ni-Nb, Ni-Nb-Sn and Ni-Nb-Al alloys were cast in the centrifugal casting machine. Alloys were melted in alumina crucibles and cast into the copper moulds. Characterizations of cast alloys were done by the use of Metallography, SEM, XRD and DSC. Fully amorphous Ni52Nb41Al7 alloy was synthesized in bulk form with 0.8 mm thickness.

La conception des ouvrages économiques a suscité de nombreux progrès dans les domaines de la modélisation et de l’optimisation, permettant l’analyse de structures de plus en plus complexes. Cependant, les conceptions optimisées sans considérer les incertitudes des paramètres, peuvent ne pas respecter certains critères de fiabilité. Pour assurer le bon fonctionnement de la structure, il est important de prendre en considération l’incertitude dès la phase de conception. Il existe plusieurs théories dans la littérature pour traiter les incertitudes. La théorie de la fiabilité des structures consiste à définir la probabilité de défaillance d’une structure par la probabilité que les conditions de bon fonctionnement ne soient pas respectées. On appelle cette étude l’analyse de la fiabilité. L’intégration de l’analyse de fiabilité dans les problèmes d’optimisation constitue une nouvelle discipline introduisant des critères de fiabilité dans la recherche de la configuration optimale des structures, c’est le domaine de l’optimisation fiabiliste (RBDO). Cette méthodologie de RBDO vise donc à considérer la propagation des incertitudes dans les performances mécaniques en s’appuyant sur une modélisation probabiliste des fluctuations des paramètres d’entrée. Dans ce cadre, ce travail de thèse porte sur l’analyse robuste et l’optimisation fiabiliste des problèmes mécaniques complexes. Il est important de tenir compte des paramètres incertains du système pour assurer une conception robuste. L’objectif de la méthode RBDO est de concevoir une structure afin d’établir un bon compromis entre le coût et l’assurance de fiabilité. Par conséquent, plusieurs méthodes, telles que la méthode hybride et la méthode optimum safety factor, ont été développées pour atteindre cet objectif. Pour remédier à la complexité des problèmes mécaniques complexes comportant des paramètres incertains, des méthodologies spécifiques à cette problématique, tel que les méthodes de méta-modélisation, ont été développées afin de bâtir un modèle de substitution mécanique, qui satisfait en même temps l’efficacité et la précision du modèle
The design of economic system leads to many advances in the fields of modeling and optimization, allowing the analysis of structures more and more complex. However, optimized designs can suffer from uncertain parameters that may not meet certain reliability criteria. To ensure the proper functioning of the structure, it is important to consider uncertainty study is called the reliability analysis. The integration of reliability analysis in optimization problems is a new discipline introducing reliability criteria in the search for the optimal configuration of structures, this is the domain of reliability optimization (RBDO). This RBDO methodology aims to consider the propagation of uncertainties in the mechanical performance by relying on a probabilistic modeling of input parameter fluctuations. In this context, this thesis focuses on a robust analysis and a reliability optimization of complex mechanical problems. It is important to consider the uncertain parameters of the system to ensure a robust design. The objective of the RBDO method is to design a structure in order to establish a good compromise between the cost and the reliability assurance. As a result, several methods, such as the hybrid method and the optimum safety factor method, have been developed to achieve this goal. To address the complexity of complex mechanical problems with uncertain parameters, methodologies specific to this issue, such as meta-modeling methods, have been developed to build a mechanical substitution model, which at the same time satisfies the efficiency and the precision of the model

Cu-based alloys are widely applied in corrosive environments. The improvement of the alloys' corrosion resistance will significantly reduce energy consumption and overexploitation of resources. To increase the resistance of copper as less corrosion resistant alloy component, nine imidazole-based compounds with different functional groups were tested as potential corrosion inhibitors. Imidazole derivatives were chosen as a potential inhibitor for copper alloys due to its diverse performance on pure Cu. Besides, CuZn alloys, CuZr crystalline and amorphous alloys, and their pure metals were tested to explore the correlations between inhibition, structure and atomic species. The determination of the performance of corrosion inhibitors on metals is a complex problem due to the mixed influence of surface condition, inhibitor-surface interaction and environmental conditions. For CuZn alloys, the a-Cu phase Cu70Zn30 alloy and non-a-Cu phase Cu30Zn70 alloy were tested. CuZr alloys are the basis of a family of metallic glasses with large glass forming ability and remarkable mechanical properties. The corrosion response of as-produced crystalline and amorphous CuxZr(100-x )alloys (x = 40, 50, 64 at. %) was tested. All alloys were immersed in 3 wt.% NaCl aqueous solution without and with 1mM inhibitor concentration. Potentiodynamic polarization measurements, electrochemical impedance spectroscopy and long-term immersion tests followed by microscopy analysis and Raman spectroscopic analysis were carried out. Comparative analysis of pure Cu and Cu70Zn30 alloy shows that the same inhibitors are effective in both alloys. A similar behavior is found with pure Zn and Cu30Zn70 alloy. However, the inhibition power shows a different value, which should be attributed to the healing effect. Defects present in most of the polished samples accelerate the pitting on these locations. The healing effect will lead to a patch on those positions, which will slow down the local attacks. All the tested CuZr amorphous alloys exhibit a much better corrosion resistance than their crystalline counterparts in the presence and absence of inhibitors. The main factor controlling the corrosion resistance of the alloys appears to be the Zr-rich (or at least equiatomic) amorphous structure, the effect of the inhibitors being secondary. Results therefore show a complex relationship between inhibitor performance, microstructure and composition of CuZr alloys. SH-ImiH-4Ph shows potential to become a global a-Cu phase alloy inhibitor and SH-BimH-5NH2 shows potential for Zn-based and CuZr alloys. Electrochemical measurements, especially long-term measurements, display a significant correlation to immersion tests. The conducted research offers some understanding on the corrosion mechanism and resistance after inhibitor application. Previous surface oxidation, defects on the surface, and inhibitor functional group are found to be the most significant factors that influence inhibition. The healing effect is also responsible for the improved efficiency of some inhibitors.
Els aliatges de coure es fan servir freqüentment en entorns corrosius. La millora de la resistència a la corrosió reduiria notablement el consum d’energia i la sobreexplotació de recursos naturals. Nou derivats de l’imidazol amb diferents grups funcionals ha estat analitzats com a potencials inhibidors de la corrosió, per tal d’augmentar la resistència a la corrosió del Cu. S’escolliren derivats de l’imidazol a la vista de la seva resposta diferent com a inhibidors de la corrosió en Cu pur. Aquest inhibidors han estat aplicats sobre els metalls purs i sobre aliatges CuZn i CuZr cristal·lines i amorfes, per tal d’explorar les correlacions entre inhibició, estructura i espècies atòmiques. La determinació de l’eficiència d’inhibició en metalls és un problema complex a causa de la influència creuada entre les condicions a la superfície, la interacció inhibidor-superfície i les condicions ambientals. En aliatges CuZn s'han estudiat les composicions Cu70Zn30 (fase a-Cu) i Cu30Zn70 (fase no-a-Cu). Els aliatges CuZr són la base d'una família de vidres metàl·lics amb gran capacitat d’amortització i excel·lents propietats mecàniques. S'ha determinat la resistència a la corrosió d'aliatges cristal·lins i amorfs de composició CuxZr (100-x) (x = 40, 50, 64 at.%). Tots els aliatges van ser analitzades en dissolució aquosa contenint un 3% de NaCl en pes, sense i amb una concentració de 1mM de l'inhibidor. S'han efectuat mesures dinàmiques de polarització, espectroscòpia d'impedància electroquímica i immersió durant períodes prolongats seguida de microscòpia i espectroscòpia Raman. L'anàlisi comparativa mostra que els inhibidors efectius en Cu pur ho són també en Cu70Zn30. Un comportament similar apareix entre Zn i Cu30Zn70. No obstant això, el poder d'inhibició mostra un valor molt diferent, que s'atribueix a l'efecte de "cicatrització". Els defectes presents en la majoria de les mostres acceleren la corrosió localitzada (pitting) en aquests punts. L'efecte de cicatrització produeix "pegats" en les mateixes posicions, el que redueix la velocitat de l'atac localment. Els aliatges CuZr cristal·lins mostren una resistència a la corrosió molt més alta que els aliatges cristal·lins amb la mateixa composició, originalment i en presència d'inhibidors. El principal factor que controla la resistència a la corrosió dels aliatges és l'alta concentració de Zr (al menys equiatòmica) en l'estructura amorfa; l'efecte dels inhibidors resulta ser secundari. Els resultats mostren una relació complexa entre l'eficiència de l'inhibidor, la microestructura i la composició dels aliatges CuZr. SH-ImiH-4Ph mostra potencial per inhibir la corrosió en aliatges on la fase dominant és a-Cu, mentre que SH-BimH-5NH2 mostra potencial com a inhibidor en aliatges on el Zn és majoritari i en aliatges CuZr. Les mesures electroquímiques, especialment de llarga durada, mostren una bona correlació amb les anàlisis d'immersió. La recerca realitzada ofereix elements de comprensió del mecanisme de corrosió en presència d'inhibidors. L'oxidació pre-existent de la superfície, els defectes en la superfície i el grup funcional de l'inhibidor són els factors dominants en l'efectivitat dels inhibidors. L'efecte de cicatrització afecta també notablement el rendiment d'alguns inhibidors.

An aged high damping alloy 53Cu 45Mn-2Al was studied both microstructurally by transmission electron microscopy (TEM) and microstructurally with two different damping measurement methods. In-situ heating and cooling observations were made with TEM in order to define the recently discovered flickering phenomenon associated with it's tweed microstructure. TEM studies were also made of an aged 53.6Cu-46.4Mn binary alloy. Damping measurements were obtained by a normalized bandwidth method applied to data from a resonant bar. This was used to determine (i) the aging condition for optimum damping, (ii) the subsequent trend of damping at room temperature for each aging condition, and (iii) the effect of an 8 HR storage at 100C on damping capacity. Damping measurements utilizing a free decay technique to determine log decrement were also used and compared to results from the normalized bandwidth method. Theses. (JES)

Thesis (M.S. in Mechanical Engineering)--Naval Postgraduate School, June 1990.
Thesis Advisor(s): Perkins, Jeff. "June 1990." Description based on title screen as viewed on March 22, 2010. DTIC Identifier(s): Alloys, Spinodal Decomposition, Flickering, Damping. Author(s) subject terms: High Damping Alloys, Spinodal Decomposition, Cu-Mn alloys, Flickering. Includes bibliographical references (p. 85-92). Also available in print.

In the course of this PhD thesis metastable Cu50Zr50-xTix (0≤ x ≤ 10) and (Cu0.5Zr0.5)100-xAlx (5 ≤ x ≤ 8) alloys were prepared and characterised in terms of phase formation, thermal behaviour, crystallisation kinetics and most importantly in terms of mechanical properties. The addition of Al clearly enhances the glass-forming ability although it does not affect the phase formation. This means that the Cu-Zr-Al system follows the characteristics of the binary Cu-Zr phase diagram, at least for Al additions up to 8 at.%. Conversely, the presence of at least 6 at.% Ti changes the crystallisation sequence of Cu50Zr50-xTix metallic glasses and a metastable C15 CuZrTi Laves phase (Fd-3m) precipitates prior to the equilibrium phases, Cu10Zr7 and CuZr2. A structurally related phase, i.e. the “big cube” phase (Cu4(Zr,Ti)2O, Fd-3m), crystallises in a first step when a significant amount of oxygen, on the order of several thousands of mass-ppm (parts per million), is added. Both phases, the C15 Laves as well as the big cube phase, contain pronounced icosahedral coordination and their formation might be related to an icosahedral-like short-range order of the as-cast glass. However, when the metallic glasses obey the phase formation as established in the binary Cu-Zr phase diagram, the short-range order seems to more closely resemble the coordination of the high-temperature equilibrium phase, B2 CuZr. During the tensile deformation of (Cu0.5Zr0.5)100-xAlx bulk metallic glasses where B2 CuZr nanocrystals precipitate polymorphically in the bulk and some of them undergo twinning, which is due to the shape memory effect inherent in B2 CuZr. Qualitatively, this unique deformation process can be understood in the framework of the potential energy landscape (PEL) model. The shear stress, applied by mechanically loading the material, softens the shear modulus, thus biasing structural rearrangements towards the more stable, crystalline state. One major prerequisite in this process is believed to be a B2-like short-range order of the glass in the as-cast state, which could account for the polymorphic precipitation of the B2 nanocrystals at a comparatively small amount of shear. Diffraction experiments using high-energy X-rays suggest that there might be a correlation between the B2 phase and the glass structure on a length-scale less than 4 Å. Additional corroboration for this finding comes from the fact that the interatomic distances of a Cu50Zr47.5Ti2.5 metallic glass are reduced by cold-rolling. Instead of experiencing shear-induced dilation, the atoms become more closely packed, indicating that the metallic glass is driven towards the more densely packed state associated with the more stable, crystalline state. It is noteworthy, that two Cu-Zr intermetallic compounds were identified to be plastically deformable. Cubic B2 CuZr undergoes a deformation-induced martensitic phase transformation to monoclinic B19’and B33 structures, resulting in transformation-induced plasticity (TRIP effect). On the other hand, tetragonal CuZr2 can also be deformed in compression up to a strain of 15%, yet, exhibiting a dislocation-borne deformation mechanism. The shear-induced nanocrystallisation and twinning seem to be competitive phenomena regarding shear band generation and propagation, which is why very few shear offsets, due to shear banding, can be observed at the surface of the bulk metallic glasses tested in quasistatic tension. The average distance between the crystalline precipitates is on the order of the typical shear band thickness (10 - 50 nm) meaning that an efficient interaction between nanocrystals and shear bands becomes feasible. Macroscopically, these microscopic processes reflect as an appreciable plastic strain combined with work hardening. When the same CuZr-based BMGs are tested in tension at room temperature and at high strain rate (10-2 s-1) there seems to be a “strain rate sensitivity”, which could be related to a crossover of the experimental time-scale and the time-scale of the intrinsic deformation processes (nanocrystallisation, twinning, shear band generation and propagation). However, further work is required to investigate the reasons for the varying slope in the elastic regime. As B2 CuZr is the phase, that competes with vitrification, it precipitates in a glassy matrix if the cooling rate is not sufficient to freeze the structure of the liquid completely. The pronounced work hardening and the plasticity of the B2 phase, which are a result of the deformation-induced martensitic transformation, leave their footprints in the stress-strain curves of these bulk metallic glass matrix composites. The behaviour of the yield strength as a function of the crystalline volume fraction can be captured by the rule of mixtures at low crystalline volume fractions and by the load bearing model at high crystalline volume fractions. In between both of these regions there is a transition caused by percolation (impingement) of the B2 crystals. Furthermore, the fracture strain can be modelled as a function of the crystalline volume fraction by a three-microstructural-element body and the results imply that the interface between B2 crystals and glassy matrix determines the plastic strain of the composites. The combination of shape memory crystals and a glassy matrix leads to a material with a markedly high yield strength and an enhanced plastic strain. In the CuZr-based metastable alloys investigated, there is an intimate relationship between the microstructure and the mechanical properties. The insights gained here should prove useful regarding the optimisation of the mechanical properties of bulk metallic glasses and bulk metallic glass composites.

Die Motivation zur Untersuchung ternärer und quaternären CuZr-Legierungen bestand in der Annahme, dass die Zugabe von Kobalt den Stabilitätsbereich von B2 CuZr bis zur Raumtemperatur erweitert und Aluminium einen signifikanten Effekt auf die Glasbildungsfähigkeit des CuZr-Systems hat. Die vorliegende Dissertation befasst sich mit der Herstellung und Charakterisierung von Cu50-xCoxZr50 (0 ≤ x ≤ 20) und Cu50-xCoxZr45Al5- (x = 2, 5, 10 und 20) Legierungen. Hierbei wurden die Phasenbildung, die thermische Stabilität, die Mikrostruktur, die Martensitbildung und die mechanischen Eigenschaften der Legierungen untersucht. Die Abhängigkeit der Phasenbildung von der Erstarrungsrate und der thermodynamischen Stabilität von Cu-Co-Zr-Legierungen zeigte, dass die Zugabe von Kobalt die Glasbildungsfähigkeit von Cu-Co-Zr-Legierungen absenkt und die stabilen kristallinen Produkte des Systems von Cu10Zr7 + CuZr2 zu (Cu,Co)Zr Phase mit einer B2 Struktur verändert. Die Ergebnisse weisen darauf hin, dass bei den schmelzgesponnene Bänder mit wenigstens 5 Atom-% Co das Glas direkt in B2 (Cu,Co)Zr kristallisiert, während Massivproben mit Co-Gehalten zwischen 0 ≤ x < 5 die monokline (Cu,Co)Zr Phase und Cu10Zr7 sowie CuZr2 beinhalten, wobei für x ≥ 10 die B2 (Cu,Co)Zr Phase bei Raumtemperatur im Gleichgewicht ist. Des Weiteren werden mit steigendem Co-Gehalt die Martensitumwandlungstemperaturen zu niedrigeren Werten verschoben. Die Phasenbildung im ternären System wird im pseudo-binären (Cu,Co)Zr-Phasendiagramm zusammengefasst, welches die Entwicklung neuer Formgedächtnislegierungen sowie metallischer Glas-Komposite bei Zugabe des Glasbildungselementes Aluminium vereinfacht. In den Vierstofflegierungen erhöht Al die Glasübergangs- und Kristallisationstemperaturen und verbessert dadurch die Glasbildungsfähigkeit des Systems. Die röntgenographische Analyse zeigte, dass die Kristallisationsprodukte der schmelzgesponnenen Bänder variieren: von Cu10Zr7 + CuZr2 + AlCu2Zr zu (Cu,Co)Zr + AlCu2Zr, wenn Co ≤ 5 und Co ≥ 10. Die Herstellung von Massivproben mit unterschiedlichen Durchmessern führte zu einem vollständig amorphen Gefüge, einem metallischen Glas-Komposit oder einem vollständig kristallinen Gefüge. Für Co ≤ 5 tritt neben (Cu,Co)Zr und AlCu2Zr ebenfalls Cu10Zr7 auf. Mittels Rasterelektronen (REM)- und Transmissionselektronenmikroskopie (TEM) erfolgte die Analyse des Einflusses von Al- und Co-Zugaben auf die Mikrostruktur von CuZr-Legierungen. Für die Cu-Co-Zr-Al-Legierungen sowie Cu30Co20Zr45Al5 (ø = 4 mm) und Cu45Co5Zr45Al5 (ø = 2 mm) wurden mikrostrukturelle Untersuchungen mittels TEM durchgeführt. Nachfolgend wurde die Heterogenität der Mikrostruktur in der Cu40Co10Zr45Al5 (ø = 2 mm) untersucht. Der Einfluss von Co auf die mechanischen Eigenschaften von rascherstarrten Cu50-xCoxZr50 (x = 2, 5, 10 und 20 Atom-%) Legierungen zeigt, dass das Verformungsverhalten der Stäbe unter Druckbeanspruchung stark von der Mikrostruktur der (Cu,Co)Zr Phase und somit von der Legierungszusammensetzung abhängt. Kobalt beeinflusst die Bruchfestigkeit der Gussproben. Weiterhin zeigen Proben mit martensitischem Gefüge eine Kaltverfestigung. Neben der Kaltverfestigung zeigen die Legierungen mit hohem Co-Gehalt eine verformungsinduzierte Martensitumwandlung und weisen zwei Streckgrenzen auf. Für die Vierstofflegierungen wurde der Einfluss der Kühlrate und der chemischen Zusammensetzung auf die mechanischen Eigenschaften untersucht. Für Cu48Co2Zr45Al5 (ø = 1.5, 2, 3 und 4 mm) und Cu45Co5Zr45Al5 (ø = 3 mm) wurde der Einfluss der Kühlrate und der Heterogenität diskutiert. Die Ergebnisse zeigen, dass die mechanischen Eigenschaften der Cu50-xCoxZr45Al5-Legierungen stark von der Makrostruktur und dem Volumenanteil der amorphen und kristallinen Phase abhängen. Die verformungsinduzierte Martensitumwandlung in Cu40Co10Zr50- und Cu40Co10Zr45Al5-Gussstäben wurde mittels hochenergetischer Röntgenstrahlung durchgeführt. Die In-situ- Druckversuche erfolgten weg- und kraftkontrolliert. Das makroskopische und mikroskopische Spannung-Dehnungs-Verhalten sowie die Phasenumwandlungskinetik wurden dabei betrachtet. Die relativen Veränderungen der vollständig integrierten Intensität der ausgewählten B2- und Martensitreflexe, die auf die Veränderungen der Volumenanteile der entsprechenden Phasen unter Verformung hinweisen, wurden als Phasenumwandlungsvolumen M/M+B2 beschrieben
The fact that the presence of Co extends the stability range of B2 CuZr to room temperature, together with the significant effect of Al on improving the glass forming ability of the CuZr system was the motivation to investigate the ternary and quaternary CuZr alloys with the aim of synthesizing BMG composites containing B2 (Cu,Co)Zr crystals. This PhD thesis deals with preparation and characterization of Cu50-xCoxZr50 (0 ≤ x ≤ 20) and Cu50-xCoxZr45Al5 (x = 2, 5, 10 and 20) alloys. The phase formation, thermal stability, microstructure, martensitic transformation and mechanical properties of these alloys were investigated. The dependence of phase formation on solidification rate and the thermodynamically stability of Cu-Co-Zr alloys reveals that the addition of Co decreases the glass forming ability (GFA) of the Cu-Co-Zr alloys and changes the stable crystalline products of the system from Cu10Zr7 + CuZr2 to (Cu,Co)Zr phase with a B2 structure. The results indicate that for the melt-spun ribbons with at least 5 % Co, the glass crystallizes directly into B2 (Cu,Co)Zr, while in the case of bulk specimens, compositions with 0 ≤ x < 5 of Co contain the monoclinic (Cu,Co)Zr phase and Cu10Zr7 and CuZr2, whereas, for x ≥ 10, the B2 (Cu,Co)Zr phase is the equilibrium phase at room temperature. Furthermore, increasing the cobalt content decreases the martensitic transformation temperatures to lower temperatures. The phase formation in the ternary system is summarized in a pseudo-binary (Cu,Co)Zr phase diagram, that helps for designing new shape memory alloys, as well as bulk metallic glass composites with the addition of glass former elements. In the quaternary alloys, Al increases the glass transition and crystallization temperatures and hence improves the GFA of the system. The X-ray analysis illustrates that for the melt-spun ribbons, the crystallization products vary from Cu10Zr7 + CuZr2 + AlCu2Zr to (Cu,Co)Zr + AlCu2Zr when Co ≤ 5 and Co ≥ 10, respectively. Depending on the cooling rates, the bulk samples represent a fully amorphous structure or BMG composites or a fully crystalline structure. For Co ≤ 5, beside (Cu,Co)Zr and AlCu2Zr, Cu10Zr7 exists as well. Scanning (SEM) and transmission (TEM) electron microscopy investigations were done to investigate the effect of Al and Co addition to the microstructure of CuZr alloys. In the case of Cu-Co-Zr-Al alloys, Cu30Co20Zr45Al5 (ɸ = 4 mm) and Cu45Co5Zr45Al5 (ɸ = 2 mm) compositions were selected for the microstructure verification using TEM. Later, the heterogeneity of the microstructure in Cu40Co10Zr45Al5 (ɸ = 2 mm) alloy was considered. The effect of Co on the mechanical properties of rapidly solidified Cu50-xCoxZr50 (x = 2, 5, 10 and 20 at.%) alloys depict that the deformation behavior of the rods under compressive loading strongly depends on the microstructure, and as a results, on the alloy composition. Cobalt affects the fracture strength of the as-cast samples; and deformation is accompanied with two yield stresses for high Co-content alloys, which undergo deformation-induced martensitic transformation. Instead samples with a martensitic structure show a work-hardening behavior. For quaternary alloys, the effects of cooling rate and chemical composition on mechanical properties of the alloys were investigated. Cu48Co2Zr45Al5 (ɸ= 1.5, 2, 3 and 4 mm) and Cu45Co5Zr45Al5 (ɸ = 3 mm) compositions were selected to discuss the effect of cooling rate and heterogeneity, respectively. The results depict that the mechanical properties of Cu50-xCoxZr45Al5 alloys strongly depend on the microstructure and the volume fraction of the amorphous and crystalline phases. The deformation-induced martensitic transformation of Cu40Co10Zr50 and Cu40Co10Zr45Al5 as-cast rods, was studied by means of high-energy X-rays. The in situ compression measurements were performed in track control and load control modes. The macroscopic and microscopic stress-strain behavior, as well as the phase transformation kinetics were considered. The relative changes in the fully integrated intensity of the selected B2 and martensite peaks, which indicate the changes in volume fraction of the corresponding phases under deformation, was described as phase transformation volume, M/M+B2

[ES] Teniendo en cuenta el agotamiento de los combustibles fósiles y la creciente concentración de CO2 en la atmósfera, la hidrogenación de CO2 es una forma prometedora de convertir el CO2 en productos químicos y combustibles de carbono de alto valor añadido. Considerando la gran influencia del tamaño de partícula, la composición química, la naturaleza del soporte y las condiciones de operación sobre el comportamiento catalítico de los catalizadores, se han desarrollado una serie de catalizadores para la hidrogenación de CO2 basados en metales abundantes no nobles y polisacáridos naturales como precursores del grafeno. En la presente tesis doctoral, las especies metálicas soportadas sobre una matriz de carbono grafítico defectuosa, con diferentes tamaños de partículas, muestran diferente actividad catalítica y selectividad para la hidrogenación de CO2. Se prepararon, de forma controlada, nanopartículas de aleaciones de Co y Co-Fe soportadas en grafenos dopados con N defectuosos, con una amplia distribución de tamaño de nanopartículas, para la reacción de Sabatier, presentando una selectividad a metano superior al 90% con valores de conversión de CO2 superiores al 85%. En el caso de un solo metal, Co o Fe, y sus aleaciones en forma de "clusters" y pequeñas nanopartículas soportadas en el mismo material, la selectividad de la hidrogenación de CO2 cambia a CO, en lugar de metano, obteniéndose un valor del 98 % y alcanzando una conversión de CO2 del 56%. Conviene resaltar que, los catalizadores basados en "clusters" de aleaciones de metal con una carga de metal incluso por debajo del 0.2 % en peso, exhiben una mayor selectividad y rendimiento que los que tienen nanopartículas de aleaciones de Co-Fe más grandes que varían de 1 a 4 nm y una carga de metal más alta en una composición similar. Siguiendo la línea de investigación de hidrogenación de CO2, se desarrollaron una serie de nanopartículas de aleaciones de Co-Fe soportadas sobre grafenos dopados con N defectuosos con distribución de tamaño de nanopartículas controlada en el rango de 7-17 nm, obteniendo una selectividad hacia hidrocarburos C2+ alrededor del 45% y una conversión del CO2 cercana al 60%. Además, se realizó un estudio comparativo de la actividad catalítica de catalizadores similares basados en Co-Fe con promotores e inhibidores para la hidrogenación de CO2, observando su influencia en la conversión y selectividad de CO2. Finalmente, además de los catalizadores basados en Co-Fe, también se han preparado catalizadores basados en Cu-ZnO mediante un método de dos pasos. Estas nanopartículas de Cu-ZnO soportadas sobre grafeno defectuoso dopado con N exhiben una alta selectividad hacia la conversión de CO2 a metanol.
[CA] Tenint en compte l'esgotament dels combustibles fòssils i la creixent concentració de CO2 en l'atmosfera, la hidrogenació de CO2 és una forma prometedora de convertir el CO2 en productes químics i combustibles de carboni d'alt valor afegit. Considerant la gran influència de la grandària de partícula, la composició química, la naturalesa del suport i les condicions d'operació sobre el comportament catalític dels catalitzadors, s'han desenvolupat una sèrie de catalitzadors per a la hidrogenació de CO2 basats en metalls abundants no nobles i polisacàrids naturals com a precursors del grafé. En la present tesi doctoral, les espècies metàl·liques suportades sobre una matriu de carboni grafític defectuosa, amb diferents grandàries de partícules, mostren diferent activitat catalítica i selectivitat per a la hidrogenació de CO2. Es van preparar, de manera controlada, nanopartícules d'aliatges de Co i Co-Fe suportades en grafens dopats amb N defectuosos, amb una àmplia distribució de grandària de nanopartícules, per a la reacció de Sabatier, presentant una selectivitat a metà superior al 90% amb valors de conversió de CO2 superiors al 85%. En el cas d'un sol metall, Co o Fe, i els seus aliatges en forma de "clústers" i xicotetes nanopartícules suportades en el mateix material, la selectivitat de la hidrogenació de CO2 canvia a CO, en lloc de metà, obtenint-se un valor del 98% i aconseguint una conversió de CO2 del 56%. Convé ressaltar que, els catalitzadors basats en "clústers" d'aliatges de metall amb una càrrega de metall fins i tot per davall del 0.2% en pes, exhibeixen una major selectivitat i rendiment que els que tenen nanopartícules d'aliatges de Co-Fe més grans que varien d'1 a 4 nm i una càrrega de metall més alta en una composició similar. Seguint la línia d'investigació d'hidrogenació de CO2, es van desenvolupar una sèrie de nanopartícules d'aliatges de Co-Fe suportades sobre grafens dopats amb N defectuosos amb distribució de grandària de nanopartícules controlada en el rang de 7-17 nm, obtenint una selectivitat cap a hidrocarburs C2+ al voltant del 45% i una conversió del CO2 pròxima al 60%. A més, es va realitzar un estudi comparatiu de l'activitat catalítica de catalitzadors similars basats en Co-Fe amb promotors i inhibidors per a la hidrogenació de CO2, observant la seua influència en la conversió i selectivitat de CO2. Finalment, a més dels catalitzadors basats en Co-Fe, també s'han preparat catalitzadors basats en Cu-ZnO mitjançant un mètode de dos passos. Aquestes nanopartícules de Cu-ZnO suportades sobre grafé defectuós dopat amb N exhibeixen una alta selectivitat cap a la conversió de CO2 a metanol.
[EN] Considering the depletion of fossil fuels and the increasing atmospheric CO2 concentration, CO2 hydrogenation is a promising way to convert CO2 into value-added carbon-containing chemicals and fuels. Taking into account the significant influences of the particle size, chemical composition, nature of the support, and operation conditions on the catalytic performance of catalysts, a series of catalysts for CO2 hydrogenation have been developed based on the use of abundant non-noble metals and natural polysaccharides as graphene precursors. In the present PhD Thesis, metal species supported on defective graphitic carbon matrix with different particle sizes show different catalytic activity and selectivity for CO2 hydrogenation. Under effective control, Co and Co-Fe alloy nanoparticles wrapped on defective N-doped graphenes with a broad nanoparticle size distribution were prepared and performed for the Sabatier reaction, exhibiting a selectivity to methane over 90 % at CO2 conversion values over 85 %. In the case of single Co or Fe metal and their alloys in the form of clusters and small nanoparticles wrapped on the same support, the selectivity for CO2 hydrogenation shifts to CO, rather than methane, reaching a conversion of 56 % with 98 % CO selectivity. It is worth noting that the metal alloy clusters-based catalysts with the metal loading even below 0.2 wt.% exhibit a higher selectivity and better performance than the ones with larger Co-Fe alloy nanoparticles ranging from 1-4 nm and higher metal loading in a similar composition. Following the research line for CO2 hydrogenation, a series of Co-Fe alloy nanoparticles supported on defective N-doped graphenes with controlled nanoparticle size distribution in the range of 7-17 nm are developed, obtaining a selectivity towards C2+ hydrocarbons about 45% with a CO2 conversion close to 60%. In addition, a comparative catalytic activity of similar Co-Fe-based catalysts with promoters and poison has been studied for CO2 hydrogenation to observe their influence on CO2 conversion and selectivity. Finally, besides Co-Fe-based catalysts, Cu-ZnO-based catalysts have also been prepared by a two-step method. These Cu-ZnO nanoparticles supported on N-doped defective graphene exhibit a high selectivity for CO2 conversion to methanol.
Peng, L. (2021). Metal Nanoparticles Wrapped on Defective Nitrogen-doped Graphitic Carbons as Highly Selective Catalysts for C02 Hydrogenation [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/172329
TESIS

Au cours de la dernière décennie, les alliages de fonderie Al-Si ont été utilisés de plus en plus comme une alternative appropriée à la fonte dans la fabrication de composants de moteurs (par exemple les culasses). Les objectifs du projet étaient d'étudier l'effet des éléments tels que le cuivre, le magnésium et le fer sur les défauts de solidification, et sur l'évolution des phases poste-eutectiques les alliages de fonderie Al-Si. Tout d’abord, les travaux antérieurs sont soigneusement examinés afin de mieux comprendre les charges de fatigue thermomécanique, les caractéristiques, les exigences et les matériaux applicables dans les composantes du moteur. Par la suite, les défauts de solidification (tendance de fissuration à chaud (HTS) et microporosité) des alliages à base d’Al-Si ont été évalués. En augmentant la teneur en Cu et en Fe des alliages, la valeur de HTS et de microporosité ont été augmentées. Les indices théoriques de fissuration à chaud ont été simulés avec un modèle de microségrégation multiphasique avec rétrodiffusion dans la phase primaire «multiphase back diffusion model». La corrélation obtenue entre les résultats expérimentaux (HTS) et les résultats simulés est excellente. L’effet de la composition chimique (Cu, Mg et Fe contenu) dans les alliages Al-Si sur l'évolution de la microstructure ont donc été étudiées. Les microstructures à l'état de coulée et à l'état de traitement thermique de mise en solution (SHT) ont été évaluées par les microscopies optique/électronique. Deux intermétalliques contenant du Mg (Q-Al5Cu2Mg8Si6, π-Al8FeMg3Si6) qui apparaissent avec une couleur grise sous le microscope optique ont été discriminés par des attaques chimiques que nous avons développées. L’analyse calorimétrique différentielle à balayage (DSC) a été utilisée pour examiner les transformations de phase survenant au cours du processus de chauffage et de refroidissement. Les calculs thermodynamiques ont été effectués pour évaluer la formation de la phase à l'état d'équilibre et hors-équilibre. Les résultats ont démontré que la séquence de solidification et la stabilité des intermétalliques contenant du Cu/Mg ont été fortement influencée par la composition chimique des alliages. La phase Q-Al5Cu2Mg8Si6 a été solidifiée soit à la même température ou plus tôt que la phase θ-Al2Cu en fonction de la teneur en Cu de l'alliage. Par ailleurs, les phases Q-Al5Cu2Mg8Si6 et π-Al8FeMg3Si6 qui étaient solubles à 505℃ dans l'alliage Al-7Si-1.5Cu-0.4mg, sont restées presque intactes dans l'alliage Al-7Si-1.5Cu-0.8mg wt.-%. Bien que l’intermétallique-AlCuFe a été à peine observé dans la microstructure de coulée, la réaction entre la phase primiare α-Al avec la phase β-Al5FeSi a causé la formation de la phase N-Al7Cu2Fe au cours de la mise en solution. La transformation de phase à l'état solide de la phase β-Al5FeSi à la phase N-Al7Cu2Fe a également été étudiée.
Over the past decade, Al-Si based foundry alloys have increasingly been used as a suitable alternative for cast iron in the fabrication of engine components. This project was aimed to study the effect of Cu, Mg and Fe elements on solidification defects (hot rearing tendency and microporosity), and on evolution of post eutectic phases in the Al-7Si (wt.-%) based alloys. Initially, the previous works and the most pertinent literatures were thoroughly reviewed to elaborate the thermo-mechanical fatigue loads, characteristics, requirements and materials applicable in engine components (mainly cylinder-head). Subsequently, the solidification defects of the Al-Si based alloys were evaluated. By increasing Cu and Fe content of the alloys, the hot tearing sensitivity and the microporosity content of the alloys were both enhanced. Multiphase back diffusion model was utilized to simulate the theoretical hot tearing indices. A very good correlation was obtained between the experimental and the theoretical hot tearing indices. Effect of the chemistry (Cu, Mg and Fe content) on microstructure evolution of the Al-Si foundry alloys was consequently studied. As-cast and solution heat treated (SHT) microstructures of the alloys were evaluated by optical- and electron-microscopy. Two etchants were developed to discriminate the Mg-bearing intermetallics (Q-Al5Cu2Mg8Si6, π- Al8FeMg3Si6) under optical microscope. Differential scanning calorimetry (DSC) was utilized to examine the phase transformations occurring during heating/cooling process. Thermodynamic computations were carried out to assess the phase formation in the equilibrium/non-equilibrium conditions. According to the predicted/experimental results, the solidification sequence and the stability of Cu/Mg bearing intermetallics are strongly influenced by the chemistry of the alloys. Q-Al5Cu2Mg8Si6 phase was solidified either at the same temperature or earlier than θ-Al2Cu phase depending the Cu content of the alloy. Moreover, Q-Al5Cu2Mg8Si6 and π- Al8FeMg3Si6 which were soluble at 505℃ in the alloy Al-7Si-1.5Cu-0.4Mg, remained almost intact in the alloy Al-7Si-1.5Cu-0.8Mg wt.-%. Tough the AlCuFe- intermetallic was barely observed in the as-cast microstructure, the reaction of α-Al with the β-Al5FeSi phase caused the formation of the N-Al7Cu2Fe phase during SHT. The solid state phase transformation (precipitation temperature and mechanism) of β-Al5FeSi to the N-Al7Cu2Fe phase was also investigated.

Secondary Al-Si-Cu-Mg based foundry alloys are widely used in automotive industry to particularly produce powertrain cast components mainly due to their good ratio between weight and mechanical properties, and excellent casting characteristics. Presence of impurity elements, such as Fe, Mn, Cr, Ti, V and Zr, in secondary Al-Si alloys is one of the critical issues since these elements tend to reduce alloy mechanical properties. There is an ongoing effort to control the formation of intermetallic phases containing transition metals, during alloy solidification. Although phases formation involving these transition metal impurities in non-grain-refined Al-Si alloys is well documented in the literature, the role of grain refinement in microstructural evolution of secondary Al-Si-Cu-Mg alloys needs further experimental investigations since chemical grain refinement is one of the critical melt treatment operations in foundries. The primary aim of this PhD work is thus defined to characterize the formation of intermetallic phases containing transition metals in secondary Al-7Si-3Cu-0.3Mg alloy before and after grain refinement by different master alloys and contribute to the understanding of the mechanisms underlying the microstructural changes occurring with the addition of grain refiner. Another critical issue related to Al-Si-Cu-Mg alloys is their limited thermal stability at temperatures above 200 oC. The operating temperature in engine combustion chamber is reported to often exceed 200 oC during service. Moreover, a further increase of operating temperature is anticipated due to the expected engine power enhancement in near future, which indicates the necessity for the development of a new creep-resistant Al alloys. Deliberate addition of transition metals is believed to yield a new heat-resistant alloy by promoting the formation of thermally stable dispersoids inside α-Al grains. This study thus also attempted to investigate the effect of adding transition metals Zr, V and Ni on the solidification processing, microstructural evolution and room/high-temperature tensile properties of secondary Al-7Si-3Cu-0.3Mg alloy, one of the most used alloys in automotive engine manufacturing. The influence of transition metal impurities on microstructural evolution of secondary Al-7Si-3Cu-0.3Mg alloy was investigated before and after chemical treatment with different master alloys: Al-10Sr, Al-5Ti-1B, Al-10Ti and Al-5B. The Al-10Zr, Al-10V and Al-25Ni master alloys were used for the experimental investigations of the effects of deliberate additions of transition metals on the solidification path, microstructure and mechanical properties of secondary Al-7Si-3Cu-0.3Mg alloy. Solidification path of the alloys was characterized by the traditional thermal analysis technique and differential scanning calorimetry (DSC). Optical microscope (OM), scanning electron microscope (SEM) equipped with energy-dispersive (EDS), wavelength-dispersive spectrometers (WDS) and electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM) equipped with EDS were used to characterize the type, morphology and distribution of the phases precipitated during solidification and heat treatment of the studied alloys. The static tensile properties of the alloys were characterized at room (20 oC) and high temperatures (200 and 300 ºC). Experimental findings indicate that the Sr-modification and grain refinement of secondary Al-7Si-3Cu-0.3Mg alloy with Al-Ti-B can be enough effective despite the presence of transition metal impurities in the material and the variation of pouring temperature. However, the V and Zr (~100 ppm each) available in secondary Al-7Si-3Cu-0.3Mg alloy tended to promote the precipitation of harmful, primary AlSiTi intermetallics during solidification of grain-refined alloy. This implies that more effective optimization of grain refiner addition level in secondary Al foundry alloys can be achieved by considering the role of transition metal impurities, Ti, V and Zr, since the formation of primary AlSiTi particles causes (1) the depletion of Ti needed for effective α-Al grains growth restriction and (2) the formation of casting defects, such as shrinkage, due to their flaky morphology. Iron available in secondary Al-7Si-3Cu-0.3Mg alloy as impurity only formed more desirable α-Al15(FeMn)3Si2 phase in non-grain refined state. After grain refinement by Al-5Ti-1B, Fe was also involved in the formation of more deleterious β-Al5FeSi phase. The TiB2 particles acted as nucleation site for β-Al5FeSi phase. Both higher cooling rate and higher Al-5Ti-1B addition levels tended to promote the formation of deleterious β-Al5FeSi at the expense of α-Al15(FeMn)3Si2 in the alloy refined by Al-5Ti-1B. This implies that rather than the ratio between Mn and Fe, the nucleation kinetics of Fe-rich intermetallics play a decisive role in the selection of competing α-Al15(FeMn)3Si2 and β-Al5FeSi intermetallic phases for the precipitation during alloy solidification. Moreover, grain refinement of secondary Al-7Si-3Cu-0.3Mg alloy by Al-5B showed comparable performance to that of Al-5Ti-1B master alloy, however, without any deleterious influence on the precipitation sequence of Fe-rich phases, i.e. deleterious β-Al5FeSi reaction remained unfavourable during alloy solidification. Experimental findings from the investigations of the effect of deliberate Zr and V addition revealed that Zr and V addition can induce the grain refinement of secondary Al-7Si-3Cu-0.3Mg alloy. While Zr addition yielded the formation of pro-peritectic Zr-rich particles, which are found to nucleate primary α-Al at low undercooling, the effect of adding V can be characterized by the enhancement of the degree of constitutional undercooling. Combined Zr and V addition showed more effective grain refinement level than their individual additions. Majority of both Zr and V added to the alloy were retained inside α-Al matrix during solidification. As a result, limited amounts of Zr and V were rejected to the interdendritic liquid by the growing α-Al dendrites, then forming small-sized and rarely distributed intermetallics. Owing to its low solid solubility in α-Al, nickel available as impurity (~ 200 ppm) or after deliberate addition (0.25 wt.%) in secondary Al-7Si-3Cu-0.3Mg alloy was mainly bound to interdendritic, insoluble intermetallics, such as Al6Cu3Ni and Al9(FeCu)Ni phases. The presence of ~ 200 ppm Ni was sufficient to diminish to a certain extent the precipitation hardening effect of Cu. Interdendritic Zr/V/Ni-rich phases remained undissolved into the α-Al matrix during solution heat treatment. Therefore, the supersaturated transition metals in α-Al solid solution obtained during solidification was only involved in the solid-state precipitation occurring during heat treatment. Unlike Cu/Mg-rich strengthening precipitates that commonly form during aging, the Zr/V-rich precipitates tended to form during solution heat treatment. Other transition metals, such as Mn, Fe, Cr and Ti, which were present as impurities in secondary Al-7Si-3Cu-0.3Mg alloy significantly promoted the formation of nano-sized Zr/V-rich precipitates inside α-Al grains. These thermally more stable precipitates, including novel α-Al(MnVFe)Si, were credited for the enhanced high-temperature strength properties of Al-7Si-3Cu-0.3Mg alloy by ~ 20 %.
Secondary Al-Si-Cu-Mg based foundry alloys are widely used in automotive industry to particularly produce powertrain cast components mainly due to their good ratio between weight and mechanical properties, and excellent casting characteristics. Presence of impurity elements, such as Fe, Mn, Cr, Ti, V and Zr, in secondary Al-Si alloys is one of the critical issues since these elements tend to reduce alloy mechanical properties. There is an ongoing effort to control the formation of intermetallic phases containing transition metals, during alloy solidification. Although phases formation involving these transition metal impurities in non-grain-refined Al-Si alloys is well documented in the literature, the role of grain refinement in microstructural evolution of secondary Al-Si-Cu-Mg alloys needs further experimental investigations since chemical grain refinement is one of the critical melt treatment operations in foundries. The primary aim of this PhD work is thus defined to characterize the formation of intermetallic phases containing transition metals in secondary Al-7Si-3Cu-0.3Mg alloy before and after grain refinement by different master alloys and contribute to the understanding of the mechanisms underlying the microstructural changes occurring with the addition of grain refiner. Another critical issue related to Al-Si-Cu-Mg alloys is their limited thermal stability at temperatures above 200 oC. The operating temperature in engine combustion chamber is reported to often exceed 200 oC during service. Moreover, a further increase of operating temperature is anticipated due to the expected engine power enhancement in near future, which indicates the necessity for the development of a new creep-resistant Al alloys. Deliberate addition of transition metals is believed to yield a new heat-resistant alloy by promoting the formation of thermally stable dispersoids inside α-Al grains. This study thus also attempted to investigate the effect of adding transition metals Zr, V and Ni on the solidification processing, microstructural evolution and room/high-temperature tensile properties of secondary Al-7Si-3Cu-0.3Mg alloy, one of the most used alloys in automotive engine manufacturing. The influence of transition metal impurities on microstructural evolution of secondary Al-7Si-3Cu-0.3Mg alloy was investigated before and after chemical treatment with different master alloys: Al-10Sr, Al-5Ti-1B, Al-10Ti and Al-5B. The Al-10Zr, Al-10V and Al-25Ni master alloys were used for the experimental investigations of the effects of deliberate additions of transition metals on the solidification path, microstructure and mechanical properties of secondary Al-7Si-3Cu-0.3Mg alloy. Solidification path of the alloys was characterized by the traditional thermal analysis technique and differential scanning calorimetry (DSC). Optical microscope (OM), scanning electron microscope (SEM) equipped with energy-dispersive (EDS), wavelength-dispersive spectrometers (WDS) and electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM) equipped with EDS were used to characterize the type, morphology and distribution of the phases precipitated during solidification and heat treatment of the studied alloys. The static tensile properties of the alloys were characterized at room (20 oC) and high temperatures (200 and 300 ºC). Experimental findings indicate that the Sr-modification and grain refinement of secondary Al-7Si-3Cu-0.3Mg alloy with Al-Ti-B can be enough effective despite the presence of transition metal impurities in the material and the variation of pouring temperature. However, the V and Zr (~100 ppm each) available in secondary Al-7Si-3Cu-0.3Mg alloy tended to promote the precipitation of harmful, primary AlSiTi intermetallics during solidification of grain-refined alloy. This implies that more effective optimization of grain refiner addition level in secondary Al foundry alloys can be achieved by considering the role of transition metal impurities, Ti, V and Zr, since the formation of primary AlSiTi particles causes (1) the depletion of Ti needed for effective α-Al grains growth restriction and (2) the formation of casting defects, such as shrinkage, due to their flaky morphology. Iron available in secondary Al-7Si-3Cu-0.3Mg alloy as impurity only formed more desirable α-Al15(FeMn)3Si2 phase in non-grain refined state. After grain refinement by Al-5Ti-1B, Fe was also involved in the formation of more deleterious β-Al5FeSi phase. The TiB2 particles acted as nucleation site for β-Al5FeSi phase. Both higher cooling rate and higher Al-5Ti-1B addition levels tended to promote the formation of deleterious β-Al5FeSi at the expense of α-Al15(FeMn)3Si2 in the alloy refined by Al-5Ti-1B. This implies that rather than the ratio between Mn and Fe, the nucleation kinetics of Fe-rich intermetallics play a decisive role in the selection of competing α-Al15(FeMn)3Si2 and β-Al5FeSi intermetallic phases for the precipitation during alloy solidification. Moreover, grain refinement of secondary Al-7Si-3Cu-0.3Mg alloy by Al-5B showed comparable performance to that of Al-5Ti-1B master alloy, however, without any deleterious influence on the precipitation sequence of Fe-rich phases, i.e. deleterious β-Al5FeSi reaction remained unfavourable during alloy solidification. Experimental findings from the investigations of the effect of deliberate Zr and V addition revealed that Zr and V addition can induce the grain refinement of secondary Al-7Si-3Cu-0.3Mg alloy. While Zr addition yielded the formation of pro-peritectic Zr-rich particles, which are found to nucleate primary α-Al at low undercooling, the effect of adding V can be characterized by the enhancement of the degree of constitutional undercooling. Combined Zr and V addition showed more effective grain refinement level than their individual additions. Majority of both Zr and V added to the alloy were retained inside α-Al matrix during solidification. As a result, limited amounts of Zr and V were rejected to the interdendritic liquid by the growing α-Al dendrites, then forming small-sized and rarely distributed intermetallics. Owing to its low solid solubility in α-Al, nickel available as impurity (~ 200 ppm) or after deliberate addition (0.25 wt.%) in secondary Al-7Si-3Cu-0.3Mg alloy was mainly bound to interdendritic, insoluble intermetallics, such as Al6Cu3Ni and Al9(FeCu)Ni phases. The presence of ~ 200 ppm Ni was sufficient to diminish to a certain extent the precipitation hardening effect of Cu. Interdendritic Zr/V/Ni-rich phases remained undissolved into the α-Al matrix during solution heat treatment. Therefore, the supersaturated transition metals in α-Al solid solution obtained during solidification was only involved in the solid-state precipitation occurring during heat treatment. Unlike Cu/Mg-rich strengthening precipitates that commonly form during aging, the Zr/V-rich precipitates tended to form during solution heat treatment. Other transition metals, such as Mn, Fe, Cr and Ti, which were present as impurities in secondary Al-7Si-3Cu-0.3Mg alloy significantly promoted the formation of nano-sized Zr/V-rich precipitates inside α-Al grains. These thermally more stable precipitates, including novel α-Al(MnVFe)Si, were credited for the enhanced high-temperature strength properties of Al-7Si-3Cu-0.3Mg alloy by ~ 20 %.

The processing window is important for the semisolid processability of alloys. Applications of semi-solid metal (SSM) processing, especially aluminium alloys have been expanding for their excellent mechanical properties. However, the alloys well suited and commercially used for SSM processing today are limited in types. The main purpose of this Ph.D. project is to understand what makes an alloy suitable for SSM processing on both aspects of thermodynamics and kinetics. This research started with a fundamental study of binary alloys based on Al-Si, Al-Cu and Al-Mg systems (wt%): Al-1Si, Al-5Si, Al-12Si and Al-17Si; Al-1Cu, Al-2Cu and Al-5Cu; Al-0.5Mg, Al-3Mg and Al-5.5Mg. These are representative of Si, Cu and Mg contents in commercial alloys used for SSM processing. The Single-Pan Scanning Calorimeter (SPSC) and Differential Scanning Calorimeter (DSC) were used to investigate the liquid fraction changes during heating and cooling of these binary alloys. Thermo-Calc and DICTRA (DIffusion-Controlled TRAnsformations) software have been used to predict the fraction liquid versus temperature taking into account both thermodynamics and kinetics. Comparison of the predictions with experimental data revealed that the simulation results show the same pattern with experimental results in the fraction liquid-temperature relationship. However, the SPSC results are closer to the prediction than DSC curves are, even with the relatively large sample size associated with SPSC. This is potentially a significant result as predicting the liquid fraction versus temperature for the heating of a billet for semi-solid processing remains one of the challenges. The results also suggest that the fraction liquid sensitivity to time should be identified as a critical parameter of the process window for semi-solid processing in addition to the fraction liquid sensitivity to temperature. For microstructure investigation, microanalysis techniques, including Scanning Electron Microscopy (SEM) and micro-indentation testing, have been used on polished sections, and compared to theoretical predictions. In addition, some parts of this project are in cooperation with General Research Institute for Nonferrous Metals (GRINM), which aims to design and develop high performance semi-solid alloys. Thermodynamic analysis (both predictions and experiments) were carried out on thixoformed 319s (2.95Cu, 6.10Si, 0.37Mg, wt%) and 201 (4.80Cu, 0.7Ag, wt%) aluminium alloys. SEM techniques and Transmission Electron Microscopy (TEM) were used for the microstructural characterisation. The results showed that the DSC curves were sensitive to microsegregation in SSM alloys and resulted in a lower liquid fraction than the cast alloys calculated through the integration method from the DSC results. Al2Cu phase in SSM alloys 319s and 201 can be dissolved into matrix up to 0.4 % before melting temperature under 3K/min heating rate when compared with 10K/min heating rate. The DSC scan rate should be carefully selected as higher heating rate can inhibit dissolution of the intermetallic phases during heating leading to less accurate liquid fractions predictions.

Fundamental understanding of atmospheric corrosion mechanisms requires an in-depth understanding on the dynamic interaction between corrosive constituents and metal/alloy surfaces. This doctoral study comprises field and laboratory investigations that assess atmospheric corrosion and metal release processes for two different groups of alloys exposed in chloride-rich environments. These groups comprise two commercial Zn-Al alloy coatings on steel, Galfan™ (Zn5Al) and Galvalume™ (Zn55Al), and four copper-based alloys (Cu4Sn, Cu15Zn, Cu40Zn and Cu5Zn5Al). In-depth laboratory investigations were conducted to assess the role of chloride deposition and alloy microstructure on the initial corrosion mechanisms and subsequent corrosion product formation. Comparisons were made with long-term field exposures at unsheltered marine conditions in Brest, France. A multitude of surface sensitive and non-destructive analytical methods were adopted for detailed in-situ and ex-situ analysis to assess corrosion product evolution scenarios for the Zn-Al and the Cu-based alloys. Scanning electron microscopy and energy dispersive spectroscopy (SEM/EDS) were employed for morphological investigations and scanning Kelvin probe force microscopy (SKPFM) for nobility distribution measurements and to gain microstructural information. SEM/EDS, infrared reflection-absorption spectroscopy (IRAS), confocal Raman micro-spectroscopy (CRM) and grazing incidence x-ray diffraction (GIXRD) were utilized to gain information on corrosion product formation and possibly their lateral distribution upon field and laboratory exposures. The multi-analytical approach enabled the exploration of the interplay between the microstructure and corrosion initiation and corrosion product evolution. A clear influence of the microstructure on the initial corrosion product formation was preferentially observed in the zinc-rich phase for both the Zn-Al and the Cu-Zn alloys, processes being triggered by microgalvanic effects. Similar corrosion products were identified upon laboratory exposures with chlorides for both the Zn-Al and the Cu-based alloys as observed after short and long term marine exposures at field conditions. For the Zn-Al alloys the sequence includes the initial formation of ZnO, ZnAl2O4 and/or Al2O3 and subsequent formation of Zn6Al2(OH)16CO3·4H2O, and Zn2Al(OH)6Cl·2H2O and/or Zn5(OH)8Cl2·H2O. The patina of Cu sheet consists of two main layers with Cu2O predominating in the inner layer and Cu2(OH)3Cl in the outer layer, and with a discontinuous presence of CuCl in-between. Additional patina constituents of the Cu-based alloys include SnO2, Zn5(OH)6(CO3)2, Zn6Al2(OH)16CO3·4H2O and Al2O3. General scenarios for the evolution of corrosion products are proposed as well as a corrosion product flaking mechanism for some of the Cu-based alloys upon exposure in chloride-rich atmospheres. The tendency for corrosion product flaking was considerably more pronounced on Cu sheet and Cu4Sn compared with Cu15Zn and Cu5Al5Zn. This difference is explained by the initial formation of zinc- and zinc-aluminum hydroxycarbonates Zn5(OH)6(CO3)2 and Zn6Al2(OH)16CO3·4H2O on Cu15Zn and Cu5Al5Zn, corrosion products that delay the formation of CuCl, a precursor of Cu2(OH)3Cl. As a result, the observed volume expansion during transformation of CuCl to Cu2(OH)3Cl, and the concomitant flaking process of corrosion products, was less severe on Cu15Zn and Cu5Al5Zn compared with Cu and Cu4Sn in chloride-rich environments. The results confirm the barrier effect of poorly soluble zinc and zinc-aluminum hydroxycarbonates Zn5(OH)6(CO3)2 and Zn6Al2(OH)16CO3·4H2O, which results in a reduced interaction between chlorides and surfaces of Cu-based alloys, and thereby reduced formation rates of easily flaked off corrosion products. From this process also follows reduced metal release rates from the Zn-Al alloys.
Bättre molekylär förståelse för metallers atmosfäriska korrosion kräver en fördjupad kunskap i det dynamiska samspelet mellan atmosfärens korrosiva beståndsdelar och metallytan. Denna doktorsavhandling omfattar laboratorie- och fältundersökningar av korrosions- och metallfrigöringsprocesser av två grupper av legeringar som exponerats i kloridrika atmosfärsmiljöer: två kommersiella Zn-Al beläggningar på stål, Galfan™ (Zn med 5% Al, förkortat Zn5Al) och Galvalume™ (Zn55Al), samt fyra kopparbaserade legeringar (Cu4Sn, Cu15Zn, Cu40Zn och Cu5Zn5Al). Undersökningar har genomförts i renodlade laboratorie-miljöer med för-deponerade NaCl-partiklar i en atmosfär av varierande relativ fuktighet. Syftet har varit att utvärdera betydelsen av kloriders deposition och legeringarnas mikrostruktur på korrosionsmekanismen samt bildandet av korrosionsprodukter. Jämförelser av korrosionsmekanismer har även gjorts efter flerårsexponeringar av samma legeringar i en marin fältmiljö i Brest, Frankrike. Undersökningarna har baserats på ett brett spektrum av analysmetoder för detaljerade studier dels under pågående atmosfärisk korrosion (in-situ), och dels efter avslutad korrosion (ex-situ). Legeringarnas mikrostruktur och tillhörande variation i ädelhet hos olika faser har undersökts med svepelektronmikroskopi och energidispersiv röntgenmikroanalys (SEM/EDS) samt med en variant av atomkraftsmikroskopi (engelska: scanning Kelvin probe force microscopy, SKPFM). Korrosionsprodukternas tillväxt har analyserats in-situ med infraröd reflektions-absorptionsspektroskopi (IRAS), samt morfologi och sammansättning av bildade korrosionsprodukter ex-situ med SEM/EDS, konfokal Raman mikro-spektroskopi (CRM) samt röntgendiffraktion vid strykande ifall (GIXRD). Det multi-analytiska tillvägagångssättet har medfört att det komplexa samspelet mellan de skilda legeringarnas mikrostruktur, korrosionsinitiering och bildandet av korrosionsprodukter kunnat studeras i detalj. En tydlig påverkan av mikrostruktur på det initiala korrosionsförloppet har kunnat påvisas. Korrosionsinitieringen sker företrädesvis i mer zinkrika faser för såväl Zn-Al- som Cu-Zn-legeringar och orsakas av mikro-galvaniska effekter mellan de mer zinkrika, mindre ädla, faserna och omgivande faser. Deponerade NaCl-partiklar påskyndar den lokala korrosionen oberoende av mikrostruktur. Snarlika sekvenser av korrosionsprodukter har kunnat påvisas såväl efter laboratorie- som fältexponeringar. För Zn-Al-legeringar bildas först ZnO, ZnAl2O4 och/eller Al2O3, därefter Zn6Al2(OH)16CO3·4H2O och Zn2Al(OH)6Cl·2H2O och/eller Zn5(OH)8Cl2·H2O. På ren koppar bildas ett inre skikt dominerat av Cu2O, ett mellanskikt av CuCl och ett yttre skikt med i huvudsak Cu2(OH)3Cl. Beroende på legeringstillsats har även SnO2 och Zn5(OH)6(CO3)2 kunnat identifieras. En mekanism för flagning av korrosionsprodukter på kopparbaserade legeringar i kloridrika atmosfärer har utvecklats. Tendensen för flagning har visat sig vara mycket mer uttalad på ren Cu och Cu4Sn än på Cu15Zn och Cu5Al5Zn. Skillnaden kan förklaras med hjälp av det tidiga bildandet av Zn5(OH)6(CO3)2 och Zn6Al2(OH)16CO3·4H2O på Cu15Zn och Cu5Al5Zn som fördröjer bildandet av CuCl, en föregångare till Cu2(OH)3Cl. Därigenom hämmas även den observerade volymexpansionen som sker när CuCl omvandlas till Cu2(OH)3Cl, en process som visar sig vara den egentliga orsaken till att korrosionsprodukterna flagar. Resultaten bekräftar barriäreffekten hos de mer svårlösliga faserna Zn5(OH)6(CO3)2 och Zn6Al2(OH)16CO3·4H2O, vilken dels resulterar i en minskad växelverkan mellan klorider och de legeringsytor där dessa faser kan bildas, och dels i en reducerad metallfrigöringshastighet.

QC 20140915

Autocorr, RFSR-CT-2009-00015 Corrosion of heterogeneous metal-metal assemblies in the automotive industry
Atmospheric corrosion and environmental metal dispersion from outdoor construction materials

碩士
國立臺灣科技大學
材料科學與工程系
99
Despite numerous studies on the research and development for high-temperature lead free solders, high-lead solder are still in used because high-temperature lead free solders also has been facing several serious problems during these years. Establishing high-temperature lead-free solder is an urgent priority. This study investigates the development of high-temperature lead-free solders and their properties by improve its wettability and oxidation resitivity after addition of Ni and Ge in Zn-Sn-Al-Cu based alloy. The solders are examined for microstructure, thermal properties, mechanical properties and investigate the interfacial reaction between Zn-Sn-Al-Cu based alloy with Cu and Ni/Cu at 300 and 350oC for 1, 2 and 4 hours. The experimental results indicate that the liquilidus temperature of Zn-Sn-Al-Cu based alloys is between 275oC to 375oC with Zn content. As Zn contents increase the (Zn) and CuZn5 increase, therefore resulting in the increase of micro-hardness and ultimate tensile strength and the addition of Al improve mechanical properties. Three or four intermetallic compounds (IMCs) are formed at the interface in the Cu/alloy diffusion couple. The reaction phases are identified as CuZn5, Al4Cu3Zn, ??nphase and CuZn is formed facing to the Cu substrate. The ??nphase is formed or not that is related to Al/Zn ratio. The IMCs are indentified as CuZn5, Al4Cu3Zn, (Zn), (Al) and?n??Sn phase in the alloys near the Ni/Cu substrate after reflow.

碩士
國立交通大學
照明與能源光電研究所
102
This paper mainly aims to study the differences in photoelectrical characteristics between reflective metal pads (APC/Cr/Au and Ag/Cr/Au) on a GaN-based light emitting diode device and the application of a chromium metal adhesion layer. Reflective metal pads with Cr/APC/Cr/Au are expected to have high reflectance than those with Cr/Ag/Cr/Au,these reflective metal pads with Cr/APC/Cr/Au also have high light output power when used on a GaN-based light emitting diode device. The reflective metal pads with Cr/APC/Cr/Au further have lower specific contact resistance when they are used on N-GaN and ITO/P-GaN, respectively. Therefore, their applications in a GaN-based light emitting diode device can more effectively reduce the series resistance of the entire device, thereby causing the overall device to have lower forward voltage. First, the measured reflectance reveals that the reflectance of Cr/APC/Cr(10Å/600Å/500Å), Cr/APC/Cr(20Å/600Å/500Å),Cr/Ag/Cr(10Å/600Å/500Å), and Cr/Ag/Cr(20Å/600Å/500Å) in the 450 nm wavelength are 89.9%, 75.0%, 92.2%, and 81.9%, respectively. They have higher reflectance by comparing with the reflectance of Cr/Au(500Å/800Å), i.e., 38.9%. Second, this paper studies the ohmic contact properties of reflective metal pads (Cr/APC/Cr/Au and Cr/Ag/Cr/Au) on N-GaN and ITO/P-GaN, respectively. Under the conditions of Cr/APC/Cr/Au(10Å/600Å/500Å/800Å), Cr/APC/Cr/Au (20Å/600Å/500Å/800Å),Cr/Ag/Cr/Au(10Å/600Å/500Å/800Å),and Cr/Ag/Cr/Au(20Å/600Å/500Å/800Å), their specific contact resistances on N-GaN and ITO/P-GaN are 5.49 × 10-4, 6.55 × 10-5, 9.61 × 10-4, 8.91 × 10-5 and 6.58 × 10-2, 5.96 × 10-2, 8.69 × 10-2, and 7.82 × 10-2 Ω-cm2, respectively. This finding shows that the reflective metal pads with Cr/APC/Cr/Au can more effectively reduce the higher specific contact resistances with Cr/Ag/Cr/Au on N-GaN and ITO/P-GaN. Third and last, this paper probes the photoelectric properties of reflective metal pads(Cr/APC/Cr/Au and Cr/Ag/Cr/Au) on a GaN-based light emitting diode device. Using a 20mA injection current, the corresponding series resistances are 23.2, 20.5, 33.6, and 26.2Ω, whereas the corresponding forward voltages are 3.25, 3.14, 3.58, and 3.41 V, respectively, under the conditions of Cr/APC/Cr/Au(10Å/600Å/500Å/800Å), Cr/APC/Cr/Au(20Å/600Å/500Å/800Å), Cr/Ag/Cr/Au(10Å/600Å/500Å/800Å), Cr/Ag/Cr/Au(20Å/600Å/500Å/800Å). Moreover, the corresponding light output powers are 23.2, 21.7, 23.6, and 22.0 mW, whereas the corresponding wall plug efficiencies are 42.3%, 39.5%, 43.1%, and 40.1%, respectively. Compared with conventional Cr/Au pad (500 Å/800 Å), their light output powers increase by 17.2%, 9.6%, 19.21%, and 11.0%, whereas their corresponding wall plug efficiencies increase by 11.6%, 8.1%, 3.1%, 0.9%, respectively. To sum up, reflective metal pads with Cr/APC/Cr/Au can more effectively reduce higher series resistances and forward voltages than those with Cr/Ag/Cr/Au on a GaN-based light emitting diode device. These reflective metal pads with Cr/APC/Cr/Au can also more effectively increase the low wall plug efficiency than those with Cr/Ag/Cr/Au on a GaN-based light emitting diode device and have high light output power.

碩士
國立高雄應用科技大學
機械與精密工程研究所
103
The work output density of shape memory alloys (SMA) are well recognized for their shape memory effect (SME) and pseudo-elastic(PE). Because of that, these alloys have attracted much attention to be used in micro/nano electromechanical systems(MEMS/ NEMS). The SMA thin films are confirmed that the shape memory properties with narrow hysteresis and a wide range of martensitic transformation temperature (Ms) of copper-based alloys thin films, towards applications for micro-actuators. Several aspects have been considered, such as fabrication procedures, characterization of the microstructure and shape memory properties. In the past, the arc-melted has to be in the majority. In this work the fabrication procedures are both of arc-melted and electron beam-melted for Cu-Al-Ni alloy bulks. Furthermore, The microstructures and the crystal structures of the Cu-Al-Ni SMA were studied by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and differential scanning calorimetry (DSC). In this experimental procedure show that the precipitate and the second phase due to influence of fabrication procedures and Composition, in which the both of two kinds of martensites, i.e. 2H and 18R , coexisting adjacent to each other in the specimen were observed. The change between the 18R and 2H stacking sequences was investigated by diffraction technique. Further experiments revealed that the β1´ martensite structure is actually of the M18R type (modified 18R) monoclinic one with its β angle very close to 90°. There is results showed the emergence of precipitates, indicating precipitation phenomenon form from metastable phase by electron beam energy of TEM. In the SMA, these precipitates affect the transformation temperatures (Ms, Mf, As, Af) and deteriorate the shape memory recoveries of these specimens. Therefore, this study investigate the processing-property and microstructure evolution of the SMA alloys. The purpose of this work is evaluating to the effectiveness of e-beam evaporation deposition for SMA thin films and comparative study composition of different on copper-based SMA. Theoretical analysis of the optimal fabrication procedures of Cu-based SMA and the nature by the method in this work can be obtained. This results will have some contribution of our study on the development of micro-electromechanical systems.

碩士
中華大學
機械與航太工程研究所
87
Brazeability of Ti-6Al-4V alloy brazed with Ag-Cu based active filler metal in vacuum environment has been investigated. Brazing processes were carried out in a vacuum of 5×10-5torr at 850℃,875℃,900℃,925℃,and 950℃for 10 minutes.The microstructure of the brazed interface was observed by using optical microscopy(OM) and scanning electron microscopy (SEM). In order to evaluate the bond joints quality, the tensile test and corrosion test were conducted as well. The Ti-6Al-4V/Ag-Cu based filler/Ti-6Al-4V brazements brazed at 875℃ for 10 minutes, the bonding strength was 601±42Mpa, which is 60% of Ti-6Al-4V base alloy’s tensile strength. The microstructures at the joints are silver solid solution and lamellar Ti-Cu-Ag and Ti-Cu-Al intermetallic compounds.Corrosion tests found these brazements failed at the brazed joint for the intermetallic compounds,which formed at its joint clearance.When the brazing system brazed at 950℃ for 10 minutes,the main microstructure at joint clearance of brazements is Ti-Cu dendritic structure and its bonding strength was only 304±36MPa.

碩士
國立臺北科技大學
材料及資源工程系研究所
98
Graphene is a two-dimensional crystal of carbon atoms arranged in a honeycomb lattice, it has high mechanical strength, high thermal conductivity, high specific surface area, and high electron mobility. Graphene is the ideal material for many dream applications, such as single electron transistors, transparent electrodes, UV light emitting diodes, gas sensors, super capacitor and biochips. This study is based on the mechanism of transition metal catalyzed graphite to diamond transition under high pressure and temperature. Copper and nickel transition metal powders are adopted to react with graphite powders in high temperature vacuum sintering furnace. After melting, the graphite flakes can be catalytically mended together by the transition metal alloy. This process is self assembling and self healing, so graphite layers can be formed on the surface of the ingot. With optimal alloy/graphite ratios and holding time, large area graphite film can be successfully prepared. The experiment consists of three parts: (1) Ratio - The ratios of C : Cu-Ni(30-70)=1 wt% : 99 wt%, and C : Cu-Ni(50-50)=0.5 wt% : 99.5 wt% are optimal. Besides, in view of the graphite film forming mechanism, graphite powder is first precipitated and separated by melting alloy then assembled as flakes in the melting alloy. After that, graphite flakes are transformed into graphite film on the surface of alloy ingot as a result of catalytic conversion process and density difference. (2) Various holding time – We observed the best character of graphite films under the condition of five-hour holding time. (3) Heat treatment – The best heat treatment temperature is 500℃ and hold for 1hr .

碩士
國立中央大學
機械工程研究所
99
We proposed with the Zr-based and Zr-Cu based metallic glass thin film (MGTF) as promising coating for aluminum alloy fatigue property enhancement. According to the four-point-bending fatigue results, 7075-T6 aluminum alloy with a 200-nm-thick Zr-based MGTF improved its fatigue life cycle 22 times at a stress level of 250 MPa than the bare one. And the other fatigue life cycle of Zr-Cu based MGTF is further improved 44 times which ups to 107 cycles. The improvements of MGTF coating samples in fatigue limit were 235 MPa (56.7 % increase) and 250 MPa (66.7 % increase) for Zr-based and Zr-Cu based glass-forming film, respectively, and 150 MPa for uncoated sample. The films actually restrict the surface offsets and cracks propagating during the fatigue test. Zr-Cu based glass-forming film have better fatigue resistance than Zr-based MGTF, the fatigue life had improved by more than 2 times under a stress of 250 MPa, due to higher hardness and strength, better plasticity, thus it exhibits better improvement in fatigue property. A 50-nm-thick Titanium buffer layer between the film and the substrate was reported adhesion enhancement. The superior mechanical properties of MGTF, such as high strength and good bending ductility, coupled with good adhesion between the film and the substrate as well as the reduced surface roughness, and high compressive residual stress of the metallic film yield the fatigue property improvement of aluminum alloy. Thus demonstrating MGTF as promising coating materials for improving the fatigue properties of materials, and further applied to aerospace, automobile industry and bicycle manufacturing etc.

碩士
大同大學
材料工程研究所
93
This study examined the amorphization behavior of Cu-Ti-Ni based alloy powders synthesized by mechanical alloying technique. The microstructural evolution during mechanical alloying of the mixed powders was investigated by both X-ray diffraction and scanning electron microscopy (SEM) . The phase stabilities of the as-milled powders were analysed by the differential scanning calorimeter. Several amorphous powders were found to exhibits a wide supercooled liquid region before crystallization. The temperature interval of the supercooled liquid region defined by the difference between Tg and Tx, ie ΔT(ΔT=Tx-Tg), is 75K for Cu40Ti40Ni20 , 83K for Cu40Ti40Ni17Sn3 ,99K for Cu40Ti40Ni16Sn4, 95K for (Cu40Ti40Ni20)96Sn4, and 82K for Cu40Ti40Ni15Si5 .As the results demonstrated, small addition of Sn and Si significantly improved the glass forming ability (GFA) of the Cu-Ti-Ni amorphous alloy.

碩士
國立清華大學
材料科學工程學系
95
The purpose of this study was to explore binary and ternary Cu-based bulk metallic glasses (BMG), which were divided into three systems: Cu-Hf-Al, Cu-Y-(M), Cu-Ti-M alloys, where M is an additive element. First, high Cu-content binary Cu-Hf BMG modified with Al, (Cu65Hf35)100-xAlx (x= 1, 2, 3, 4, 6) were studied. With only x= 2, the glass-forming ability (GFA) is greatly improved to form bulk glassy rod up to at least 3 mm in diameter. The microstructure consists of inhomogeneous amorphous phases. The Cu-Y binary system was chosen to study the GFA on compositions around the eutectic points and their modification. The microstructure of as-cast Cu-Y rods contained amorphous and crystalline mixture phases. According to the XRD results the best glass forming alloy is Cu78Y22. The further addition of Ag improves the GFA. The composition (Cu78Y22)97Ag3 was very close to form fully 1 mm BMG rod. Finally, we tried to develop the ternary BMGs based on high Cu content Cu-Ti BMG. The best result is the Cu50Ti40Zr10 glassy rod with the diameter at least 1 mm. The Cu-Y-M ternary alloys are brittle and poor electrochemical resistance due to their structure that contained amorphous and crystalline phases. Fully amorphous Cu-Hf-Al system showed the best mechanical properties with a compressive fracture strength up to 2340 MPa and a plastic strain up to about 1 % due to the inhomogeneous amorphous phases. Cu50Ti40Zr10 alloy performed low corrosion current density, 10-5 A/cm2, in 1 N H2SO4 + 0.01 N NaCl solution showed excellent electrochemical property, and its compressive fracture strength is up to about 2000 MPa.

碩士
大同大學
材料工程研究所
91
This study examined the amorphization behavior of Cu-based alloy powders synthesized by mechanical alloying technique. The microstructural evolution during mechanical alloying of the mixed powders was investigated by both X-ray diffraction and scanning electron microscopy（SEM）. The phase stabilities of the as-milled powders were studied by the DSC measurement. According to the results, after 5 hours of milling, the mechanically alloyed powders were amorphous at Cu-based alloys with B and Si. The thermal stability of the Cu-based amorphous powders was also investigated by differential scanning calorimeter (DSC). As the results demonstrated, the amorphous powders were found to exhibit a wide supercooled liquid region before crystallization. The temperature interval of the supercooled liquid region defined by the difference between Tg and Tx, i.e. ΔT （ΔT=Tg-Tx）, are: Cu50Zr27Ti20B3（72K）、Cu50Zr25Ti20B5（77K）、Cu50Zr24Ti20B5Si1（85K）、Cu50Zr20Ti20B5Si5（89K）. Finally, small additions of B and Si significantly improved the glass forming ability（GFA） of the Cu-based amorphous alloys.

碩士
國立臺北科技大學
製造科技研究所
92
In this study, four kinds of Cu-Mn based brazing alloys were developed with the active element Si addition. The compositions of the brazing alloys were identified according to their microstructure phase diagrams. Besides, the melting points of these developed brazing alloys were evaluated through the DSC analysis. The brazing temperatures were identified in accordance with the compositions and melting points mentioned above. Two brazing experiments were then performed: First, braze diamond grits onto 304 stainless steel substrate using the developed brazing alloys as filler metals. Second, place the brazing alloys on top of CVD diamond films and heat them to the brazing temperatures. Then, by means of chemical etching technique, the researcher removed the diamond grits from the matrix. The surface of the diamond grits removed was then analyzed by scanning electron microscopy and X-ray diffractometry. In addition, the performances of the brazing alloys on top of diamond films were evaluated via wettability observation, scanning electron microscopy（SEM）, X-ray diffractometry（XRD）, Raman analysis, and microhardness tests. The results of the study show that the M3 brazing alloy has the lowest melting point（834°C）, smallest wetting angle and best spreading ability. It is also observed that silicon and manganese both diffused to the vicinity of diamond. The intermetallic layer was formed between diamond grits and brazing alloys. The intermetallic layer was identified as Mn7C3 for M0, M1 alloys and Mn5SiC for M2, M3, M4 alloys. The findings will hopefully contribute to the manufacture of diamond tools.

碩士
大同大學
材料工程學系(所)
101
This study is examined the amorphization behavior of the Cu-Ti-Zr-based alloy powders with 10 at% Zr (99.0 at% purity) synthesized by mechanical alloying technique. The compositions of the alloys were near the eutectic compositions in the Cu-Ti-Zr ternary phase diagram by CALPHAD technique. As the results demonstrated , the ternary Cu-Ti-Zr alloys of compositions ranging from Cu-50-80 at% , Ti-10-40 at% and 10 at% Zr were not found to exhibit a glass transition temperature(Tg). By addition of silicon to the Cu60Ti30Zr10 system , some amorphous powders were found to exhibit a wide supercooled liquid region before crystallization. The temperature interval of the supercooled liquid region (ΔTx) and the activation energy of crystallization (Ec) are 76K , 221.7 kJ/mole for （Cu60Ti30Zr10）99Si1 and 84.7K , 237.8 kJ/mole for （Cu60Ti30Zr10）97Si3 , respectively . Finally , small additions of Si significantly improved the glass forming ability of the Cu-Ti-Zr-based amorphous alloys.

碩士
義守大學
材料科學與工程學系
106
Amorphous alloys have excellent mechanical properties, but it lack of ability of plastic deformation and dutility at room temperature. In order to improve these disadvantage, there are many methods that can improve the properties have been developed. For example, thermal treatments, adding of elements, rolling and so on. Zr53Cu30Ni9Al8, this bulk metallic glasses has good glass forming ability, its γm is about 0.739 and wide supercooled liquid region, its ΔTx is about 80K. In this study, for research the working ability of bulk metallic glasses at room temperature, the Cu sheets have been chosen to place at the upside and downside of Zr53Cu30Ni9Al8 bulk metallic glasses to carry out the roll bonding to disperse stress distribution and achieve the goal of average deformation, make bulk metallic glasses and Cu sheet become a composite material. The thin metal coating slows down shear band dynamics and retards its attainment to a critical unstable state. It not only is beneficial to working of bulk metallic glasses but also can keep the thermal properties of bulk metallic glasses, that is different from warm rolling. This study also through Zr53Cu30Ni9Al8 bulk metallic glasses roll bonding with Cu sheet to investigate how the process of roll bonding influence the effet of roll bonding, like surface treatments, the rolling direct of roll bonding, the reduction rate of roll bonding and the thickness of bulk metallic glasses.

碩士
大同大學
材料工程學系(所)
96
This study examined the amorphization behavior of Cu-Ti based alloy powders synthesized by mechanical alloying technique and investigation of consolidation by vacuum hot pressing and vacuum hot extrusion. The phase stabilities of as-milled powders were studied by DSC measurement at 5K/min heating rate. The amorphous powders were found to exhibit a wide supercooled liquid region before crystallization. The temperature interval of the supercooled liquid region (ΔTx) is 114K for Cu40Ti40Ni15Sn5, 59K for Cu40Ti40Ni15Si5, 78K for Cu50Ti40Sn5B5, 88K for Cu50Ti40Ni5B5 respectively. Surface oxidation of powders in milling and consolidation processes led to larger amount of porosity and extruding failure. In addition, the hardness of the bulk amorphous alloys is 658.6HV for Cu40Ti40Ni15Sn5, 624.5HV for Cu40Ti40Ni15Si5, 617.6HV for Cu50Ti40Sn5B5, and 604.5HV for Cu50Ti40Ni5B5. It leads to better wear resistance for less weight loss as hardness increasing. Furthermore, Cu40Ti40Ni15Sn5 and Cu40Ti40Ni15Si5 amorphous alloys were found to exhibit a better corrosion resistance evaluated by potentiodynamic polarization measurements in 3.5wt% NaCl solution.

Die Motivation zur Untersuchung ternärer und quaternären CuZr-Legierungen bestand in der Annahme, dass die Zugabe von Kobalt den Stabilitätsbereich von B2 CuZr bis zur Raumtemperatur erweitert und Aluminium einen signifikanten Effekt auf die Glasbildungsfähigkeit des CuZr-Systems hat. Die vorliegende Dissertation befasst sich mit der Herstellung und Charakterisierung von Cu50-xCoxZr50 (0 ≤ x ≤ 20) und Cu50-xCoxZr45Al5- (x = 2, 5, 10 und 20) Legierungen. Hierbei wurden die Phasenbildung, die thermische Stabilität, die Mikrostruktur, die Martensitbildung und die mechanischen Eigenschaften der Legierungen untersucht. Die Abhängigkeit der Phasenbildung von der Erstarrungsrate und der thermodynamischen Stabilität von Cu-Co-Zr-Legierungen zeigte, dass die Zugabe von Kobalt die Glasbildungsfähigkeit von Cu-Co-Zr-Legierungen absenkt und die stabilen kristallinen Produkte des Systems von Cu10Zr7 + CuZr2 zu (Cu,Co)Zr Phase mit einer B2 Struktur verändert. Die Ergebnisse weisen darauf hin, dass bei den schmelzgesponnene Bänder mit wenigstens 5 Atom-% Co das Glas direkt in B2 (Cu,Co)Zr kristallisiert, während Massivproben mit Co-Gehalten zwischen 0 ≤ x < 5 die monokline (Cu,Co)Zr Phase und Cu10Zr7 sowie CuZr2 beinhalten, wobei für x ≥ 10 die B2 (Cu,Co)Zr Phase bei Raumtemperatur im Gleichgewicht ist. Des Weiteren werden mit steigendem Co-Gehalt die Martensitumwandlungstemperaturen zu niedrigeren Werten verschoben. Die Phasenbildung im ternären System wird im pseudo-binären (Cu,Co)Zr-Phasendiagramm zusammengefasst, welches die Entwicklung neuer Formgedächtnislegierungen sowie metallischer Glas-Komposite bei Zugabe des Glasbildungselementes Aluminium vereinfacht. In den Vierstofflegierungen erhöht Al die Glasübergangs- und Kristallisationstemperaturen und verbessert dadurch die Glasbildungsfähigkeit des Systems. Die röntgenographische Analyse zeigte, dass die Kristallisationsprodukte der schmelzgesponnenen Bänder variieren: von Cu10Zr7 + CuZr2 + AlCu2Zr zu (Cu,Co)Zr + AlCu2Zr, wenn Co ≤ 5 und Co ≥ 10. Die Herstellung von Massivproben mit unterschiedlichen Durchmessern führte zu einem vollständig amorphen Gefüge, einem metallischen Glas-Komposit oder einem vollständig kristallinen Gefüge. Für Co ≤ 5 tritt neben (Cu,Co)Zr und AlCu2Zr ebenfalls Cu10Zr7 auf. Mittels Rasterelektronen (REM)- und Transmissionselektronenmikroskopie (TEM) erfolgte die Analyse des Einflusses von Al- und Co-Zugaben auf die Mikrostruktur von CuZr-Legierungen. Für die Cu-Co-Zr-Al-Legierungen sowie Cu30Co20Zr45Al5 (ø = 4 mm) und Cu45Co5Zr45Al5 (ø = 2 mm) wurden mikrostrukturelle Untersuchungen mittels TEM durchgeführt. Nachfolgend wurde die Heterogenität der Mikrostruktur in der Cu40Co10Zr45Al5 (ø = 2 mm) untersucht. Der Einfluss von Co auf die mechanischen Eigenschaften von rascherstarrten Cu50-xCoxZr50 (x = 2, 5, 10 und 20 Atom-%) Legierungen zeigt, dass das Verformungsverhalten der Stäbe unter Druckbeanspruchung stark von der Mikrostruktur der (Cu,Co)Zr Phase und somit von der Legierungszusammensetzung abhängt. Kobalt beeinflusst die Bruchfestigkeit der Gussproben. Weiterhin zeigen Proben mit martensitischem Gefüge eine Kaltverfestigung. Neben der Kaltverfestigung zeigen die Legierungen mit hohem Co-Gehalt eine verformungsinduzierte Martensitumwandlung und weisen zwei Streckgrenzen auf. Für die Vierstofflegierungen wurde der Einfluss der Kühlrate und der chemischen Zusammensetzung auf die mechanischen Eigenschaften untersucht. Für Cu48Co2Zr45Al5 (ø = 1.5, 2, 3 und 4 mm) und Cu45Co5Zr45Al5 (ø = 3 mm) wurde der Einfluss der Kühlrate und der Heterogenität diskutiert. Die Ergebnisse zeigen, dass die mechanischen Eigenschaften der Cu50-xCoxZr45Al5-Legierungen stark von der Makrostruktur und dem Volumenanteil der amorphen und kristallinen Phase abhängen. Die verformungsinduzierte Martensitumwandlung in Cu40Co10Zr50- und Cu40Co10Zr45Al5-Gussstäben wurde mittels hochenergetischer Röntgenstrahlung durchgeführt. Die In-situ- Druckversuche erfolgten weg- und kraftkontrolliert. Das makroskopische und mikroskopische Spannung-Dehnungs-Verhalten sowie die Phasenumwandlungskinetik wurden dabei betrachtet. Die relativen Veränderungen der vollständig integrierten Intensität der ausgewählten B2- und Martensitreflexe, die auf die Veränderungen der Volumenanteile der entsprechenden Phasen unter Verformung hinweisen, wurden als Phasenumwandlungsvolumen M/M+B2 beschrieben.
The fact that the presence of Co extends the stability range of B2 CuZr to room temperature, together with the significant effect of Al on improving the glass forming ability of the CuZr system was the motivation to investigate the ternary and quaternary CuZr alloys with the aim of synthesizing BMG composites containing B2 (Cu,Co)Zr crystals. This PhD thesis deals with preparation and characterization of Cu50-xCoxZr50 (0 ≤ x ≤ 20) and Cu50-xCoxZr45Al5 (x = 2, 5, 10 and 20) alloys. The phase formation, thermal stability, microstructure, martensitic transformation and mechanical properties of these alloys were investigated. The dependence of phase formation on solidification rate and the thermodynamically stability of Cu-Co-Zr alloys reveals that the addition of Co decreases the glass forming ability (GFA) of the Cu-Co-Zr alloys and changes the stable crystalline products of the system from Cu10Zr7 + CuZr2 to (Cu,Co)Zr phase with a B2 structure. The results indicate that for the melt-spun ribbons with at least 5 % Co, the glass crystallizes directly into B2 (Cu,Co)Zr, while in the case of bulk specimens, compositions with 0 ≤ x < 5 of Co contain the monoclinic (Cu,Co)Zr phase and Cu10Zr7 and CuZr2, whereas, for x ≥ 10, the B2 (Cu,Co)Zr phase is the equilibrium phase at room temperature. Furthermore, increasing the cobalt content decreases the martensitic transformation temperatures to lower temperatures. The phase formation in the ternary system is summarized in a pseudo-binary (Cu,Co)Zr phase diagram, that helps for designing new shape memory alloys, as well as bulk metallic glass composites with the addition of glass former elements. In the quaternary alloys, Al increases the glass transition and crystallization temperatures and hence improves the GFA of the system. The X-ray analysis illustrates that for the melt-spun ribbons, the crystallization products vary from Cu10Zr7 + CuZr2 + AlCu2Zr to (Cu,Co)Zr + AlCu2Zr when Co ≤ 5 and Co ≥ 10, respectively. Depending on the cooling rates, the bulk samples represent a fully amorphous structure or BMG composites or a fully crystalline structure. For Co ≤ 5, beside (Cu,Co)Zr and AlCu2Zr, Cu10Zr7 exists as well. Scanning (SEM) and transmission (TEM) electron microscopy investigations were done to investigate the effect of Al and Co addition to the microstructure of CuZr alloys. In the case of Cu-Co-Zr-Al alloys, Cu30Co20Zr45Al5 (ɸ = 4 mm) and Cu45Co5Zr45Al5 (ɸ = 2 mm) compositions were selected for the microstructure verification using TEM. Later, the heterogeneity of the microstructure in Cu40Co10Zr45Al5 (ɸ = 2 mm) alloy was considered. The effect of Co on the mechanical properties of rapidly solidified Cu50-xCoxZr50 (x = 2, 5, 10 and 20 at.%) alloys depict that the deformation behavior of the rods under compressive loading strongly depends on the microstructure, and as a results, on the alloy composition. Cobalt affects the fracture strength of the as-cast samples; and deformation is accompanied with two yield stresses for high Co-content alloys, which undergo deformation-induced martensitic transformation. Instead samples with a martensitic structure show a work-hardening behavior. For quaternary alloys, the effects of cooling rate and chemical composition on mechanical properties of the alloys were investigated. Cu48Co2Zr45Al5 (ɸ= 1.5, 2, 3 and 4 mm) and Cu45Co5Zr45Al5 (ɸ = 3 mm) compositions were selected to discuss the effect of cooling rate and heterogeneity, respectively. The results depict that the mechanical properties of Cu50-xCoxZr45Al5 alloys strongly depend on the microstructure and the volume fraction of the amorphous and crystalline phases. The deformation-induced martensitic transformation of Cu40Co10Zr50 and Cu40Co10Zr45Al5 as-cast rods, was studied by means of high-energy X-rays. The in situ compression measurements were performed in track control and load control modes. The macroscopic and microscopic stress-strain behavior, as well as the phase transformation kinetics were considered. The relative changes in the fully integrated intensity of the selected B2 and martensite peaks, which indicate the changes in volume fraction of the corresponding phases under deformation, was described as phase transformation volume, M/M+B2.

Glass forming ability (GFA) in the Pr-rich Pr-(Cu, Ni)-Al alloys at or near the eutectic points was systematically studied. It was found that the GFA in the pseudo-ternary alloys of Pr-(Cu, Ni)-Al is higher than that of the ternary alloys of Pr-Cu-Al. Two eutectic compositions in Pr-(Cu, Ni)-Al alloys were found by DSC, namely, Pr₆₈(Cu₀.₅Ni₀.₅)₂₅Al₇ and Pr₅₂(Cu₀.₅Ni₀.₅)₂₅Al₂₃ (at %). The later one shows better GFA than the first one. However, the best GFA was obtained at an off-eutectic composition of Pr₅₄(Cu₀.₅Ni₀.₅)₃₀Al₁₆, which can be formed in fully amorphous rod with diameter of 1.5 mm by copper mould casting. The deviation of the best GFA composition from the eutectic point [Pr₆₈(Cu₀.₅Ni₀.₅)₂₅Al₇] was explained in terms of the asymmetric coupled eutectic zone and the higher glass transition temperature Tg on the hypereutectic side.
Singapore-MIT Alliance (SMA)

碩士
國立高雄應用科技大學
機械與精密工程研究所
94
This research chooses the Cu54Zr22Ti18Ni6-xSix alloys to study, and uses the vacuum melting furnace to melt alloys under the argon atmosphere. The additions of silicon replace with nickel to mix the Cu-based alloys. The Cu-based bulk amorphous alloys prepared by arc melting and copper mold casting. The sample uses DSC for analysis of thermal property, uses micro-sclerometer for analysis of the mechanical property, uses XRD for the analysis of phase, and uses TEM for the analysis of microstructure. The Cu-based bulk amorphous alloys carry on the clotting time assay and valuate the hemocompatibility. The research exhibited the glass transition temperature（Tg）of the Cu-based bulk amorphous alloys at about 725K. And the Cu54Zr22Ti18Ni4Si2 amorphous alloys have the highest ΔTx at 64K. The Cu-based bulk amorphous alloys have the highest hardness at Hv 708±12 than those have the hardness at Hv 543±8 of Cu-based crystalline alloys. The Cu-based bulk amorphous alloys also have good hemocompatibility.

碩士
大同大學
材料工程學系(所)
94
This study examined the amorphization feasibility of Mg-Cu-based alloy powders synthesized by mechanical alloying technique with a high energy SPEX 8000-D ball mixer. The microstructural evolution and phase stabilities during mechanical alloying of the mixed powders were investigated by X-ray diffraction and scanning electron microscopy and differential scanning calorimeter. Several amorphous powders were found to exhibit a wide supercooled liquid region , ie ΔT(ΔT=Tx-Tg), is 55K for Mg40Cu40Ti20, 53K for Mg40Cu35Ti25, 51K for Mg40Cu35Ti23B2, 62K for Mg40Cu35Ti21Sn4, and 74K for Mg40Cu35Ti21Ni5. As the results demonstrated, small addition of Sn and Ni significantly improved the glass forming ability (GFA) of the Mg-Cu-Ti amorphous alloy.

碩士
大同大學
材料工程研究所
94
This study examined the amorphization feasibility of Mg-Cu-based alloy powders synthesized by mechanical alloying technique with a high energy SPEX 8000-D ball mixer. The microstructural evolution and phase stabilities during mechanical alloying of the mixed powders were investigated by X-ray diffraction and scanning electron microscopy and differential scanning calorimeter. Several amorphous powders were found to exhibit a wide supercooled liquid region , ie ΔT(ΔT=Tx-Tg), is 55K for Mg40Cu40Ti20, 53K for Mg40Cu35Ti25, 51K for Mg40Cu35Ti23B2, 62K for Mg40Cu35Ti21Sn4, and 74K for Mg40Cu35Ti21Ni5. As the results demonstrated, small addition of Sn and Ni significantly improved the glass forming ability (GFA) of the Mg-Cu-Ti amorphous alloy.

碩士
大同大學
材料工程學系(所)
94
This study examined the amorphization behavior of Cu-based alloy powders synthesized by mechanical alloying technique. The microstructural evolution during mechanical alloying of the mixed powders was investigated by both X-ray diffraction（XRD）and scanning electron microscopy（SEM）. The phase stabilities of the as-milled powders were analysed by the differential scanning calorimeter. Several amorphous powders were found to exhibit a wide supercooled liquid region before crystallization. The temperature interval of the supercooled liquid region defined by the difference between the glass transition temperature（Tg）and the crystalline temperature（Tx）, ie DT（DT＝Tx－Tg）, is 117.95 K for Cu50Ti40Fe10, 77.62 K for Cu50Ti35B15, 73.99 K for Cu60Ti40Mg10, 91.82 K for Cu55Ti40Sn5, 95.02 K for Cu50Ti40Sn10, 81.13 K for Cu60Ti35Sn5, 102.3 K for Cu50Ti45Sn5, 103.25 K for Cu50Ti40Sn9B1, 95.86 K for Cu50Ti40Sn7B3, and 110.88 K for Cu50Ti40Sn5B5. As the results demonstrated, small addition of B significantly improved the glass forming ability（GFA）of the Cu-Ti-Sn amorphous alloy.

The microstructure, and phase selections of La₆₆Al₁₄(Cu, Ni)₂₀ alloy were studied by Bridgman solidifications, and composite materials of dendrites in amorphous matrix or micro- and nano- sized eutectic matrix were formed with different cooling rates. The volume fraction of the dendrite phase reaches a maximum at the cooling rate of about 15 K/s, the secondary dendrite arm spacing λ₂ decreases from 4.3 µm to 0.6 µm with the increasing of cooling rate R, and obeys the equation of λ₂R⁰.⁵⁷=1.74µm(K/s)R⁰.⁵⁷. The compression strength, as well as the elastic strain limit of the dendrite/amorphous matrix composite are 600 MPa, and 2.3%, respectively. Improved ductility was observed for the dendrite amorphous matrix composites with more dendrite phase by slow cooling rate.
Singapore-MIT Alliance (SMA)

碩士
國立臺北科技大學
車輛工程系所
104
This study focuses on the thermoelectric generating properties of an alloy, fabricated by mixing P-type (Bi2Te3)x(Sb2Te2)x ternary alloy powder with copper and through a cold-pressed sintering manufacturing process. The characteristics of these alloys were studied using X-ray diffraction, energy dispersive spectroscopy, and scanning electron microscopy. Moreover, these thermoelectric chips were analyzed with respect to their thermoelectric properties such as thermal conductivity, electric conductivity, Seebeck coefficient, thermoelectric merits. The electric power was measured on motorcycle exhaust at temperature difference. Three types of thermoelectric ternary alloy were fabricated in this study, namely P-type (Bi2Te3)x(Sb2Te2)x, N-type Bi2Te3-xSex, and P-type blended with 3% copper. The maximum Dimensionless figure of Merit(ZT) of the P-type corresponds to a temperature of 381.2 K, with a maximum value of 0.259216, a coefficient of thermal conductivity of 1.15 W/mK, an conductivity of 138 S/m, and a Seebeck coefficient of 237.3 μV/K. For the N-type powder, these values were 381 K, 0.0762, 1.08 W/mK, 107 S/m, and -141.9 μV/K, respectively. For the P-type blended with copper, these were 400.8 K, 0.28056, 2.12 W/mK, 786 S/m, and 137.2 μV/K, respectively. The calculated ZT of the P-type with copper was 9% higher than that of the P-type without copper. Thermoelectric generator fabricated with copper foil using unprocessed P-type and N-type powders had their highest power values at 382.32 pW when the temperature difference was 109 K. Thermoelectric generator fabricated with pure copper via sputtering process using unprocessed P-type or N-type powders had their highest power (247.296 pW) at a temperature difference of 114.5 K. Thermoelectric generator made of P-type powder with copper and thermoelectric generator made of unprocessed N-type powder with copper foil had the highest power at a temperature difference of 109.5 K, corresponding to a maximum power value of 469.268 pW. These results show that the Dimensionless figure of Merit of the P-type thermoelectric alloy blended with copper is 0.28056, highest at 400.8 K temperature. The Dimensionless figure of Merit value is greater than that of the P-type thermoelectric alloy without copper, which is 0.2574. Due to the increase of electric conductivity of 470%, much higher than the increase of thermal conductivity of 84%, the overall Dimensionless figure of Merit increase is 9% when we input the data into the Dimensionless figure of Merit calculation formula. The result demonstrates that the excellent conductivity of copper can enhance the Dimensionless figure of Merit value. The Dimensionless figure of Merit value can increase by 9% when adding 3% copper to the alloy.

The present study focuses on the effect of alloying elements, namely, strontium (Sr), titanium (Ti), zirconium (Zr), scandium (Sc) and silver(Ag) individually or in combination, on the performance of a newly developed Al-2%Cu based alloy. A total of thirteen alloy compositions were used in the study. Tensile test bar castings were prepared employing the low pressure die casting (LPDC) technique. The test bars were solution heat treated at 495°C for 8 hours, followed by quenching in warm water, and then subjected to different isochronal aging treatments using an aging time of 5 hours and aging temperatures of 155°C, 180°C, 200°C, 240°C and 300°C. Tensile testing of as-cast and heat-treated test bars was carried out at room temperature using a strain rate of 4 x 10-4s-1. Five test bars were used per alloy composition/condition. Hardness measurements were also carried out on these alloys using a Brinell hardness tester. The microstructures of selected samples were examined using optical microscopy and electron probe microanalysis (EPMA). The results showed that adding Ti in the amount of 0.15 wt% in the form of Al-5%Ti-1%B master alloy is sufficient to refine the grains in the cast structure in the presence of 200 ppm Sr (0.02 wt%). Addition of Zr and Sc did not contribute further to the grain refining effect. The main role of addition of these two elements appeared in the formation of complex compounds with Al and Ti. Their presence resulted in extending the aging temperature range before the onset of softening. Mathematical analysis of the hardness and tensile data was carried out using the Minitab statistical software program. It was determined that the alloy containing (0.5wt% Zr + 0.15wt% Ti) is the most effective in maximizing the alloy tensile strength over the range of aging temperatures, from 155°C to 300°C. Addition of Ag is beneficial at high aging temperatures, in the range of 240°C-300°C. However, it is less effective compared to the (Zr + Ti)-containing alloy. Addition of Sc does not appear to improve the alloy performance beyond what is achieved by the addition of Zr. From a plot of ultimate tensile strength (UTS) versus percent elongation (%El) values, the following equation was obtained to represent the strength-ductility relationship: UTS (MPa) = -32 %El + 393 with a fit of R2 = 0.83. Cette étude se concentre sur l’effet les éléments d’alliage, à savoir, le strontium (Sr), le titane (Ti), le zirconium (Zr), le scandium (Sc) et l'argent (Ag), individuellement ou en combinaison, sur la performance d’un nouvel alliage Al-2%Cu développé récemment. Treize compositions d'alliages sont utilisées dans l'étude. Des éprouvettes d’essai ont été préparées en utilisant la technologie de coulée à basse pression (LPDC). Les éprouvettes ont été mises dans une solution à 495 ° C pendant 8 heures suivi d'une trempe à l'eau tiède, puis soumis à différents traitements de vieillissement isochrones durant 5 heures, à différentes températures 155°C, 180°C, 200°C, 240°C et 300°C. Les essais en traction des échantillons ainsi traités, ont été effectués, à température ambiante en utilisant une vitesse de déformation de 4 x 10-4s-1. Cinq éprouvettes ont été utilisées par composition d’alliage / température de vieillissement. Des mesures de dureté ont également été effectuées sur ces alliages à l'aide d'un testeur de dureté Brinell. Les microstructures des échantillons sélectionnés ont été examinées par microscopie optique et microanalyse à sonde électronique (EPMA). Les résultats montrent que l'ajout de Ti en une proportion de 0,15% en poids sous forme d’alliage Al-5% Ti-1% B est suffisant pour affiner les grains de la structure de coulée en présence de 200 ppm de Sr (0,02% en poids). L’ajout de Zr et de Sc ne contribue pas davantage à l'effet d'affinage du grain. Le rôle principal de l'addition de ces deux éléments est apparu dans la formation de composés complexes avec Al et Ti. Leur présence a donné lieu à l'extension de la plage de températures de vieillissement avant le début de ramollissement. L'analyse mathématique des données de dureté et de traction a été réalisée en utilisant le logiciel de statistique Minitab. Il a été déterminé que l'alliage contenant 0,5% en poids de Zr + 0,15% en poids de Ti est le plus efficace pour maximiser la résistance à la traction de l'alliage dans la plage de températures de vieillissement de 155 ° C jusqu’à 300 ° C. L'addition d’Ag est bénéfique à haute température de vieillissement dans la plage de 240 ° C-300 ° C. Cependant, il est moins efficace par rapport à l’alliage contenant l' Zr + Ti. L'addition de Sc ne semble pas améliorer les performances de l'alliage au-delà de ce qui est réalisé par l'addition de Zr. A partir d’une courbe de la résistance à la traction (UTS) versus les valeurs du pourcentage d'allongement (% El), nous avons obtenu l'équation suivante représentant la relation force-ductilité: UTS (MPa) = -32 % El + 393 avec un ajustement de R2 = 0.83.

碩士
國立臺灣大學
機械工程學研究所
98
Microstructural evolution and bonding strength of infrared brazed Fe3Al and stainless steels(SS) using Au-based and CuMn-based fillers, respectively, are studied. Firstly the wetting experiments using these braze alloys are conducted to make sure the suitable brazing temperature. Al2FeNi, Fe3Al and AlAu2 intermetallics are found in the joint of AuPdNi (Au-8wt.%Pd-22wt.%Ni) braze alloy brazed at 980℃ and all specimens are fractured in brittle. For AuCu(Au-20wt.%Cu) braze alloy, the brazed joint is fractured along the central β-phase in which the fracture exhibits ductile/brittle mode(s) with different brazing conditions. The highest shear strength for AuCu filler is 327MPa for specimen brazed at 880℃×300s. Raising the brazing time or temperature will deteriorate the strength due to the fracture mode transfers to brittleness. For infrared brazed 304, 422 and 440C stainless steels using Cu-33.7%Mn filler, a continuous interfacial (γFe,γMn) phase is found in between the braze and SS which is not well bonded with (Cu,γMn) primary phase in the brazed joint. Thus some cracks are observed in between (γFe,γMn) and (Cu,γMn) due to the thermal expansion mismatch of these two phases. In addition, solidification shrinkage voids or impurities are also observed in the central region of the joint and the fracture mode along this central voids/impurities is ductile with the shear strength of 280MPa for brazing 304 and 422 SS brazed at 875oC×180s. Cu-33.7%Mn filler alloyed with Ni can improve the joint properties, but increase slightly the fillers’ melting points. The Ni alloyed CuMn fillers can effectively wet all SS at appropriate temperatures and the interfacial cracks in between (γFe,γMn) and (Cu,γMn) phase are greatly reduced with increasing the Ni addition.

This PhD thesis presents an innovative poly(vinyl)alcohol-based film forming system, specifically devised to obtain a controllable and selective cleaning of ancient copper-based artifacts. Traditional cleaning procedures of metallic artifacts are commonly performed by mechanical and/or chemical methods. Unfortunately, both these methods present some limits, mainly related to poor selectivity, high invasiveness and scarce control over the cleaning procedures. The main advantage of the cleaning system presented here, consists in the simultaneous chemical and mechanical action, guaranteed respectively by the presence of a confined complexing agent specific for Cu(II) ions (EDTA, Rochelle salt, polyamines) and by the removal of the final film through a peeling action. The physico-chemical characterization of the cleaning system was carried out through different methods (gravimetry, thermal analysis, rheology and ATR-FTIR spectroscopy) in order to study the kinetics of films formation and their mechanical properties. Finally, cleaning tests were firstly performed on different artificially aged samples, then on real cases of study. Questa tesi di dottorato presenta un innovativo sistema filmante a base di polivinilalcol, sviluppato specificamente per ottenere una pulitura controllabile e selettiva su manufatti antichi in lega base-rame. Le tradizionali procedure di pulitura di manufatti metallici sono comunemente eseguite tramite metodi chimici e/o meccanici. Sfortunatamente, entrambi questi metodi, presentano alcuni limiti legati principalmente a scarsa selettività, elevata invasività e assenza di controllo sulle procedure di pulitura. Il principale vantaggio del sistema pulente qui presentato consiste nella simultanea azione chimica e meccanica, garantita rispettivamente dalla presenza di un agente complessante confinato, specifico per gli ioni Cu(II) (EDTA, sale di Rochelle, poliammine) e dalla rimozione del film finale tramite un'azione di peeling. La caratterizzazione chimico-fisica del sistema pulente è stata eseguita tramite diversi metodi (gravimetria, termoanalisi, reologia, spettroscopia ATR-FTIR) in modo da studiare le cinetiche di formazione dei film e le loro proprietà meccaniche. Infine, test di pulitura sono stati eseguiti inizialmente su provini invecchiati artificialmente e poi su casi studio reali.

Le développement de nouveaux alliages, caractérisés par un rapport résistance-poids élevé et par un faible coût de production est un des objectifs majeurs de l'industrie de l'automobile afin de réduire les émissions de CO2 en réduisant le poids des pièces tout en conservant les propriétés mécaniques à haute température. L'alliage Al-2%Cu contenant 2%Cu, l%Si, 0.4%Mg, 0,42%Fe, 0.7%Mn et 0.02%Ti est l'un de ces alliages. Sa faible teneur en Cu et Si associé à un niveau acceptable de la résistance à la traction, permet à ce dernier de remplacer un certain nombre d'alliages comme le 319 pour des applications similaires telles que la coulée de culasses et de bases de moteur. En tant que nouvel alliage, il nécessite une enquête approfondie afin d'optimiser différentes caractéristiques telle la coulabilité, la microstructure et les propriétés mécaniques. Cette étude a été entreprise afin d'étudier les effets des additifs chimiques comme le zirconium et le scandium sur la microstructure, les propriétés de traction et la susceptibilité à la déchirure à chaud. Cette enquête a été réalisée à partir de 31 compositions d'alliage (Al-2%Cu) qui ont été divisés en trois catégories d'alliages principaux liés à la microstructure, les propriétés de traction et les enquêtes sur la déchirure à chaud. À titre comparatif, sept compositions de l'alliage 206 (Al-4%Cu) ont également été employées. Dans la première catégorie, dix alliages ont été coulés utilisent comme principaux additifs le Zr et le Se en combinaison avec le Ti-B, le Sr et l'Ag sous des conditions de refroidissement lent d'environ 0,3°C/s et à des concentrations relativement élevées de 0,5%Zr et 0,5%Sc. Un certain nombre d'intermétalliques primaires de Zr, Se et Zr-Sc ont été observés dans les alliages étudiés, à savoir la phase étoilée Al3(Sci-xZrx), les phases AI3SC, V-AISC2S12, A^Zr, en plus de deux autres composés intermétalliques de Zr. Il a été observé que les cristaux A^Zr servent de noyaux pour les phases étoilées qui croient par la précipitation des couches d'A^Sc, avec la substitution progressive des atomes Se par les atomes Zr. Également, la phase en étoile continue de croître à l'état solide par l'absorption de Se pour ainsi former la phase AI3SC, observée sous la forme de spirale sur les bords de la particule. Des composés intermétalliques inconnus ternaires AlZrSi et quaternaires AlZrTiSi ont également été détectés. Il a été constaté que les additions combinées de Zr et Se ont grandement modifiées la taille et la morphologie des grains de l'alliage de base. La taille des grains diminue proportionnellement avec l'augmentation de la fraction volumique des intermétaîliques résultants de l'ajout combiné de Zr et de Se qui, à son tour, conduit à la formation à profusion de la phase étoilée. Les effets bénéfiques des éléments de transition Zr, Se, Ti à affiner la taille des grains a-Al et à transformer la morphologie d'un précipité dendritique à tm non-dendritique mène, indirectement, à une réduction sensible de la taille des composés intermétalliques tels que les phases a - Fe et AfcCu. Dans la seconde catégorie, dix-sept alliages différents ont été préparés en utilisant différentes additions de Zr, Se, Ti-B, Sr, Ag et Si. Ces alliages ont été divisés en quatre11 sous-groupes, comme suit: Zr-Ti, Zr-Srs Zr-Sc et les alliages de silicium. Les barreaux pour les essais de traction (Vitesse de refroidissement 7°C/s) coulés de ces alliages ont été mis en solution pour une période de 8 heures à 490°C, puis durci par vieillissement à des temps de 2, 4, 6, 10, 16, 24 et 48h à 180°C et 0.5, 1, 1.5, 2, 4, 6, 10, 16, 24 et 48h à 220°C. Il a été signalé que les additions combinées de Zr-Ti, Zr-Sr, Zr-Sc réduit considérablement la taille des grains de l'alliage de base de 219 microns à 104-46 um étant donné que ces éléments forment des intermétalliques trialuminide primaire y compris Al3(Sci-xZrx), Al3(Scj.x. yZrxTiy), et AlsZr qui agissent comme sites de nucléation pour les grains a-Al, produisant ainsi une structure fine non dendritique. La morphologie raffinée non-dendritique produite par les additions combinées de Zr-Ti, Zr-Sr, Zr-Sc a entraîné une réduction d'environ 65% dans la fraction de surface de la phase Ai-2%Cu dans l'alliage de base, et à une réduction de la porosité d'environ 50%. Une augmentation de 2%Si a également produit les mêmes résultats, provoquée par l'augmentation de la teneur en Al-Si eutectique. Le durcissement maximal est atteint après des vieillissements de ÎOh et 24h à 180°C et de lh et 2h à 220°C. Les groupes d'alliage Zr-Sr et Zr-Ti ont fournis la meilleure amélioration des propriétés de mécaniques de l'alliage de base Al-2%Cu alors que les groupes Zr-Sc et Si occupent le troisième et quatrième niveau, respectivement. L'alliage contenant 0.02%Sr-0.7%Zr a fourni la plus grande limite à la rupture et des valeurs de résistance de 383 MPa et 326 MPa, respectivement, après 4h de vieillissement à 180°C. La résistance de l'alliage augmente dans le groupe d'alliage Zr-Ti en raison de l'augmentation de la teneur en Zr de 0,15% à 0,7% après un vieillissement de IOh à 180°C. Cette augmentation peut être attribuée aux dispersoïdes A^Zr et Als(Zri xTix) agissant en tant que sites de nucléation hétérogène pour les phases durcies par vieillissement, à l'action modifiante du Zr sur la phase AfeCuMg et à Faction du Zr-Ti à produire une structure de grains raffinés non- dendritiques. Les additions combinées de Zr-Sr et Sr-Ti produisent les meilleurs niveaux d'allongement de tous les alliages étudiés, comme en témoignent les alliages contenant 0.02%Sr-0.15%Ti et 0.02%Sr-0.7%Zr. Ces niveaux améliorés sont le résultat des effets de la modification du Sr sur les particules ot-Fe, ainsi que le rôle du Zr et du Ti à produire une structure non dendritique QJ-AI. L'alliage contenant 0.02%Sr-0.15%Ti a montré le plus haut niveau de résistance au ramollissement au cours du vieillissement à 220°C en raison des effets respectifs de la modification et du raffinage du Sr et du Ti sur la microstructure. La troisième catégorie d'alliage comprend six alliages sélectionnés dans la seconde catégorie afin d'étudier les effets de la composition chimique et des paramètres du moule sur la susceptibilité à ia déchirure à chaud (HTS) du nouvel alliage Al-2%Cu. Les résultats HTS ont été comparés avec l'alliage 206. Généralement F alliage de base Al-2%Cu a donné une plus grade résistance à la déchirure à chaud que l'alliage 206. Une température du moule élevée est bénéfique dans la réduction de la susceptibilité à la déchirure à chaud des alliages Al-2%Cu et 206 par une baisse de la valeur HTS de 21 à 3 et 9, respectivement. La température du moule est passée de 250°C à 450°C. Le raffinement de la structure des grains obtenus avec les additions de Zr-Ti ou Ti a diminué la gravité de la déchirure à chaud suite à l'augmentation du nombre de film inter granulaire liquide par unité de volume et a retardé l'atteinte du point de cohérence. L'augmentation de la teneur en silicium réduit considérablement la vulnérabilité à la déchirure à chaud de l'alliage Al-2%Cu; cette réduction est attnbuable à une augmentation de la fraction volumique de l'eut ectique, et une diminution du point de fusion de l'alliage. L'ajout du Sr a détérioré la résistance à la déchirure à chaud en raison de la formation d'oxydes de Sr et à l'extension de l'échelle de congélation de l'alliage. Il a été signalé que les particules os-Fe peuvent gêner la propagation de la fissure lors de la déchirure à chaud.

碩士
國立臺灣大學
材料科學與工程學研究所
97
Microstructural evolution and bonding strength of infrared brazed Fe3Al using Ag, Cu, and BAg-8 braze alloys have been studied. The joint of the Ag-brazed specimen only contains Ag-rich phase alloyed with Al. The shear strength isn’t affected by the brazing time and reaches 127MPa for specimens brazed at 980oC×300s with the ductile fracture of Ag-rich phase. The microstructure and shear strength of infrared brazed Fe3Al using pure Cu at 1100oC are strongly dependent upon the brazing time in which the brazed joint changes from Cu-rich phase into β1’ (N18R) martensite phase, and causes different fracture mechanism and bonding strength. The highest shear strength reachs 291MPa for the specimen brazed at 1100℃×300s with the mixture of brittle and ductile phases in the joint. The microstructure of the Fe3Al joint brazed by BAg-8 contains Ag-rich and Cu-rich phases eutectic for all brazing conditions. The shear strength increases slightly with increasing the brazing time because the Al is alloyed in the Cu-rich matrix. The highest shear strength of 181MPa is acquired from the 800℃×600s brazed specimen. The analyses of dynamic wetting angles and microstructures of Ag-based braze alloys on 304, 422 and 440C substrates are performed. Experimental results shows that Sn added into Ag-Cu braze alloy can reduce its melting point effectively but can not improve its wettability for stainless steel. The Ag-Cu-Sn braze alloy with adding Mn can reduce the wetting angle on stainless steel. The more the Mn content , the better the wettability it has. The best wettability is the Ag-Cu-Sn-10wt.%Mn alloy and its microstructure after wetting tests consistsd of Ag-rich and copper-rich phases. Meanwhile, increasing the Mn content results in the copper-rich phases in the braze changing from complex phases (Cu3Sn, Cu4MnSn, Cu-rich phases) into single Cu-rich phase with many Ag-rich precipitates.