Dissertations / Theses on the topic 'Metallic glass, bulk metallic glass composites, mechanical properties'

In the past, it has been found that CuZr-based BMG composites containing B2 CuZr crystals in the glassy matrix display significant plasticity with obvious work hardening. In this work, it was tried to provide a strategy for pinpointing the formation of CuZr-based BMG composites, to modify the microstructures of these composites, and to clarify their yielding and deformation mechanisms. In order to pinpoint the formation of CuZr-based BMG composites, the phase formation and structural evolution of 11 kinds of CuZr-based alloy systems, altogether 36 different compositions, during heating and quenching processes were investigated. An endothermic event between the crystallization and melting peaks was found to be associated with a eutectoid transformation of the B2 CuZr phase. With the addition of elements to the CuZr-based alloys, this endothermic peak(s) shifts to lower or higher temperatures, implying that minor element additions can change the thermal stability of the B2 CuZr phase. By considering the thermal stability of the supercooled liquid, i.e. its resistance against crystallization, and the thermal stability of the B2 CuZr phase, a new strategy to select compositions, which form metastable CuZr-based composites consisting of an amorphous phase and B2 CuZr crystals, is proposed. It is characterized by a parameter, K = Tf /TL, where Tf and TL are the final temperature of the eutectoid transformation during heating and the liquidus temperature of the alloy, respectively. Based on this criterion, the present CuZr-based alloys are classified into three types. For Type I alloys with lower K values, it is difficult to obtain bulk metallic glass (BMG) composites. For Type III alloys with higher K values, BMG composites with larger dimensions are prone to be fabricated, whereas only moderate-sized BMG composites can be obtained for Type II possessing intermediate K values. Accordingly, CuZr-based BMG composites containing B2 CuZr phase in the glassy matrix for different alloy systems were successfully fabricated into different dimensions. For the sake of controlling the formation of the B2 CuZr phase in the glassy matrix and then changing the deformability of CuZr-based BMG composites, different methods were also used to fabricate these composites by: (1) introducing insoluable/high-melting particles; (2) appropriate re-melting treatments of master alloys; and (3) a new flash heating and quenching method. It was demonstrated that the volume fraction, size and distribution of the B2 phase in the glassy matrix can be controlled as well using the methods above. In order to clarify the excellent mechanical properties of CuZr-based BMG composites, the yielding and plastic deformation mechanisms of CuZr-based BMG composites were investigated based on SEM, XRD, and TEM observations. With the volume fraction of amorphous phase (famor) decreasing from 100 vol.% to 0 vol.%, a single-to-“double”-to-“triple”-double yielding transition was found. For the monolithic CuZr-based BMGs and their composites with the famor ³ 97.5 ± 0.5 vol.%, only one yielding at a strain of ~2% occurs, which is due to the formation of multiple shear bands in the glassy matrix, and the associative actions of the shear banding and the martensitic transformation (MT), respectively. When the famor is less than 97.5 ± 0.5 vol.%, a “yielding” occurs at a low strain of ~1%, which results from the yielding of B2 CuZr phase and the onset of the MT within B2 CuZr phase. When the famor is larger than 55 ± 3 vol.%, a “yielding” observed at strains >8% is ascribed from the operation of dislocations with a high density as well as partial de-twinning. It was also found that with the famor decreasing, the deformation mechanism gradually changes from a shear-banding dominated process, to a process being governed by the MT in the crystalline phase, resulting in different plastic strains. Owing to the importance of the MT and the shear banding to the deformation of CuZr-based BMG composites, the details of the MT and the shear banding process were investigated. On one hand, it was found that the MT temperatures of CuZr-based martensitic alloys have a clear relationship with the respective electronic structure and the lattice parameter of the equiatomic CuZr intermetallics. The MT temperatures of the studied alloys can be evaluated by the average concentration of valence electrons. Additional elements with larger atomic radius can affect the stacking fault energy and the electronic charge density redistribution, resulting in the difference of the electronic structures. On the other hand, the formation and multiplication of shear bands for CuZr-based BMG composites is associated with the storage and dissipation of the partial elastic energy during the plastic deformation. When microstructural inhomogeneities at different length scales are introduced into the glassy matrix, the elastic energy stored in the sample-machine system during the plastic deformation is redistributed, resulting in a transition of shear banding process from a chaotic behavior to a self-organized critical state. All in all, our studies and observations provide an understanding of the formation, deformation, and microstrcutural optimization of CuZr-based BMG composites and give guidance on how to improve the ductility/toughness of BMGs
In letzter Zeit zeigte sich, dass massive Cu-Zr-basierte metallische Glaskomposite, welche B2 CuZr-Kristallite in der amorphen Matrix enthalten, eine ausgeprägte Plastizität mit klarer Kaltverfestigung aufweisen. Im Rahmen dieser Arbeit wurde versucht, eine Strategie zur zielgenauen Einstellung der Phasenbildung und des dazugehörigen Gefüges von massiven CuZr-basierten Glas-Matrix-Kompositen bereitzustellen, sowie deren Fließ- und Verformungsmechanismen aufzuklären. Es wurden elf verschiedene CuZr-basierte Legierungssysteme, insgesamt 36 verschiedene Zusammensetzungen, während Heiz- und Abschreckprozessen untersucht, um die Phasenbildung samt Gefüge von massiven CuZr-basierten Glas-Matrix-Kompositen zielgenau einzustellen. Bei CuZr-basierten metallischen Gläsern kann eine endotherme Reaktion zwischen Kristallisation und Schmelzvorgang der eutektoiden Umwandlung von B2 CuZr zugeordnet werden. Mit Zugabe verschiedener Elemente zur CuZr-Basislegierung kann diese Umwandlung zu höheren bzw. niedrigeren Temperaturen verschoben werden. Bereits geringe Beimischungen beeinflussen die thermische Stabilität der B2 CuZr-Phase. Unter Berücksichtigung der thermischen Stabilität, sowie des Widerstands gegen Kristallisation der unterkühlten Schmelze und der B2 CuZr-Phase wurde eine neue Strategie zur Auswahl des Zusammensetzungsgebiets metastabiler CuZr-Legierungen verschiedener Durchmesser vorgeschlagen. Dieser Widerstand kann durch den Parameter K=Tf/TL beschrieben werden, wobei Tf die Endtemperatur der eutektoiden Umwandlung und TL die Liquidustemperatur sind. Basierend auf diesem Parameter können die untersuchten CuZr-basierten Legierungen in drei Klassen unterteilt werden. Für Legierungen vom Typ I mit niedrigeren K-Werten, ist es schwer massive metallische Glas-Komposite (BMG-Komposite) zu erhalten. Im Gegensatz dazu lassen sich für Legierungen vom Typ III, mit höheren K-Werten, BMG-Komposite mit größeren Probendurchmessern herstellen und Legierungen vom Typ II mit einem mittleren K-Wert mit moderaten Probendurchmessern erzeugt werden. Folglich wurden CuZr-basierte Glas-Matrix-Komposite verschiedener Legierungssysteme mit B2-Phase in der amorphen Matrix erfolgreich in unterschiedlichen Geometrien hergestellt. Zur Kontrolle der Ausbildung der B2-Phase in der amorphen Matrix wurden unterschiedliche Methoden verwendet, um duktile CuZr-basierte BMG-Komposite herzustellen: (1) Einbringen von unlöslichen, hochschmelzenden Partikeln; (2) geeignete Wiederaufschmelzbehandlungen der Vorlegierungen; (3) eine neue Schnellerhitzungs- und -Abschreckmethode. Es konnte gezeigt werden, dass der Volumenanteil, sowie die Größe und Verteilung der B2-Phase in der amorphen Matrix durch die oben genannten Methoden kontrolliert werden können. Um die mechanischen Eigenschaften hinsichtlich des Fließens und der plastischen Deformationsmechanismen von CuZr-basierten BMG-Kompositen aufzuklären, wurden diese näher mittels Rasterelektronenmikroskopie, Röntgenbeugung und Durchstrahlungs-elektronenmikroskopie untersucht. Mit sinkendem Volumenanteil der amorphen Phase (famor) von 100 vol.% auf 0 vol.% kann ein Übergang von einer über zwei zu drei Fließgrenzen beobachtet werden. Für monolithische CuZr-basierte BMGs und ihre Komposite mit einem Anteil famor ≥ 97.5 ± 0.5vol.% erfolgt das Fließen ab einer Stauchung von ~2% durch Ausbildung von mehreren Scherbänden in der amorphen Matrix bzw. dem Zusammenwirken des dazugehörigen Scherens und der Martensitumwandlung. Bei einem Anteil famor unter 97.5 ± 0.5 vol.% findet ein Fließen bei niedrigerer Stauchung von ~1% statt. Dies geschieht aufgrund des Fließens und der beginnenden martensitischen Umwandlungen der B2 CuZr-Phase. Bei einem Anteil famor größer als 55 ± 3 vol.% kann ein Fließen oberhalb einer Stauchung von 8% durch die Interaktion von Versetzungen bei hoher Versetzungsdichte sowie partiellem „Entzwillingen“, beobachtet werden. Es wurde herausgefunden, dass mit sinkendem famor der Verformungsmechanismus schrittweise von einem Scherband dominierten zu einem von der martensitischen Umwandlung dominierten Mechanismus übergeht. Dieser Übergang führt zu Unterschieden in der plastischen Verformung. Da für das Verformungsverhalten von CuZr-basierten BMG-Kompositen die deformationsinduzierte martensitische Umwandlung und die Entstehung sowie Ausbreitung von Scherbändern von herausragender Bedeutung sind, wurden sie näher untersucht. Einerseits wurde herausgefunden, dass die Umwandlungstemperatur der martensitischen Umwandlung von CuZr-basierten martensitischen Legierungen in klarer Beziehung zur entsprechenden Elektronenstruktur und der Gitterkonstanten der äquiatomaren intermetallischen CuZr-Phasen stehen. Die martensitischen Umwandlungstemperaturen der untersuchten Legierungen können über die mittlere Valenzelektronenkonzentration ausgewertet werden. Zusätzliche Elemente mit größerem Atomradius können die Stapelfehlerenergie und die Ladungsdichteverteilung ändern, was in unterschiedliche Elektronenstrukturen mündet. Andererseits ist die Entstehung und Vervielfachung von Scherbändern in CuZr-basierten BMG-Kompositen verbunden mit der Speicherung und Dissipation der partiellen elastischen Energie während der plastischen Verformung. Durch das Einbringen von Gefügeinhomogenitäten unterschiedlicher Größe in die Glasmatrix, wird die elastische Energie, die im System Probe-Maschine gespeichert ist, während der plastischen Deformation umverteilt. Dies führt zu einem Übergang des Schervorgangs von chaotischem Verhalten zu einem selbstorganisierten kritischen Zustand. Insgesamt stellen unsere Untersuchungen und Beobachtungen ein Verständnis der Ausbildung, Verfomung und Gefügeoptimierung von CuZr-basierten BMG-Kompositen bereit und sollen als Leitfaden zur Verbesserung der Duktilität bzw. Zähigkeit von BMGs dienen

The large elastic limit, the strength close to the theoretical limit, the excellent magnetic properties and good corrosion resistance of bulk metallic glasses (BMGs) make them promising for several applications such as micro-geared motor parts, pressure sensors, Coriolis flow meters, power inductors and coating materials. The main limitation of these materials is their reduced macroscopic ductility at room temperature, resulting from an inhomogeneous deformation concentrated in narrows shear bands. The poor ductility can be overcome by the incorporation of a ductile second phase in the glassy matrix to form composites, which exhibit a better balance between strength and ductility. Different types of BMG composites have been developed to date but considerable plastic strain during tensile or bending tests has been only obtained for composites with in-situ formation of the second phase during solidification. Among these in-situ formed composites, significant tensile ductility has been only observed for two types of alloys so far: TiZrBe-based and CuZr-based BMG composites. The former precipitate dendrites of the cubic β-(Ti,Zr) phase in the glass matrix, whereas the latter combine spherical precipitates of the cubic B2-CuZr shape memory phase within the glass. The CuZr-based BMG composites have certain advantages over the TiZrBe-based composites such as the absence of Be, which is a toxic element, and exhibit a strong work-hardening behaviour linked to the presence of the shape memory phase. This concept of “shape memory” BMG composites has been only applied to CuZr-based alloys so far. It is worth investigating if such a concept can be also used to enhance the plasticity of other BMGs. Additionally, the correlation between microstructure, phase formation and mechanical properties of these composites is still not fully understood, especially the role of the precipitates regarding shear band multiplication as well as the stress distribution in the glassy matrix, which should be significantly influenced by the precipitates. The aim of the present work is to develop a new family of shape memory bulk metallic glass composites in order to extend the concept initially developed for CuZr-based alloys. Their thermal and mechanical properties shall be correlated with the microstructure and phase formation in order to gain a deeper understanding of the fundamental deformation mechanisms and thermal behaviour. A candidate to form new shape memory BMG composites is the pseudo-binary TiCu-TiNi system because bulk glassy samples with a critical casting thickness of around 1 mm have been obtained in the compositional region where the cubic shape memory phase, B2-TiNi, precipitates. This phase undergoes a martensitic transformation to the orthorhombic B19-TiNi during cooling at around 325 K. The B2- and B19-TiNi exhibit an extensive deformation at room temperature up to 30% during tensile loading. Compositions in the Ti-Cu, Ti-Cu-Ni, Ti-Cu-Ni-Zr, Ti-Cu-Ni-Zr-(Si) and Ti-Cu-Ni-Co systems were selected based on literature data and on a recently proposed λ+Δh1/2 criterion, which considers the effect of atomic size mismatch between the elements and their electronic interaction. Samples were then produced by melt spinning (ribbons) and Cu-mould suction casting (rods and plates). The investigation started in the Ti-Cu system. A low glass-forming ability (GFA) was observed with formation of amorphous phase only in micrometer-thick ribbons and the results showed that the best glass former is located around Ti50Cu50. Considering that the GFA of the binary alloys can be further improved with additions of Ni, new Ti-Cu-Ni shape memory BMG composites were then developed in which the orthorhombic Ti(Ni,Cu) martensite precipitates in the glassy matrix. These alloys exhibit a high yield strength combined with large fracture strain and the precipitates show a reversible martensitic transformation from B19 to B2-type structure at a critical temperature around 320 K (during heating). The amorphous matrix stabilizes the high-temperature phase (B2 phase), which causes different transformation temperatures depending on whether the precipitates are partially or completely embedded in the glassy matrix. The deformation starts in the softer, crystalline phase, which generates a heterogeneous stress distribution in the glassy matrix and causes the formation of multiple shear bands. The precipitates also have the important function to block the fast movement of shear bands and hence retard fracture. However, the size of such composites is limited to 1 mm diameter rods because of their low GFA, which can be further improved by adding CuZr. New Ti-Cu-Ni-Zr composites with diameter ranging from 2 to 3 mm were developed, which consist mainly of spherical precipitates of the cubic B2-(Ti,Zr)(Cu,Ni) and the glassy phase. The interrelation between composite strength and volume fraction of B2 phase was analysed in detail, which follows the rule of mixture for values lower than 30 vol.% or the load-bearing model for higher values. The fracture strain is also affected by the volume fraction of the respective phases with a maximum observed around 30 vol.% of B2 phase, which agrees with the prediction given by the three-body element model. It was observed that the cubic B2 phase undergoes a martensitic transformation during deformation, resulting in a strong work hardening and a high fracture stress of these alloys. The GFA of the Ti-Cu -based alloys can be further increased by minor additions of Si. A maximum GFA is observed for additions of 1 and 0.5 at.% Si to binary Ti-Cu or quaternary Ti-Cu-Ni-Zr alloys, respectively. This optimum GFA results from the formation of a lower amount of highly stable Ti5Si3 precipitates, which act as nuclei for other crystalline phases, and the increased stability of the liquid and the supercooled liquid. The addition of Co has the opposite effect. It drastically decreases the GFA of Ti-Cu-Ni alloys and both the martensitic transformation temperature and their mechanical behaviour seem to correlate with the number and concentration of valence electrons of the B2 phase. The transformation temperature decreases by increasing the concentration of valence electrons. An excellent combination of high yield strength and large fracture strain occurs for Ti-Cu-Ni-Zr and Ti-Cu-Ni-Zr-Si alloys with a relatively low amount of CuZr, with a fracture strain in compression almost two times larger than the one usually observed for CuZr-based composites. For instance, the Ti45Cu39Ni11Zr5 alloy exhibit a yield strength of 1490±50 MPa combined with 23.7±0.5% of plastic strain. However, a reduced ductility was found for the CuZr-richer Ti-Cu-Ni-Zr compositions, which results from the precipitation of the brittle Cu2TiZr phase in the glassy matrix. The present study extends the concept of “shape memory BMG matrix composites” originally developed for CuZr-based alloys and delivers important insights into the correlation between phase formation and mechanical properties of this new family of high-strength TiCu-based alloys, which upon further optimization might be promising candidates for high-performance applications such as flow meters, sensors and micro- and mm-sized gears
Auf Grund der hohen Elastizitätsgrenze, Festigkeiten, die nahe an der theoretischen Grenze liegen, sehr guten magnetischen Eigenschaften, sowie einer guten Korrosionsbeständigkeit erscheint der Einsatz massiver metallischer Gläser (BMG) vielversprechend in zahlreichen Gebieten, wie z.B. in Mikro-Getriebemotorteilen, Coriolis-Massendurchflussmessern, Drucksensoren, Speicherdrosseln und als Beschichtungsmaterialien. Der Einsatz dieser Materialien wird jedoch hauptsächlich durch ihre begrenzte makroskopische Duktilität bei Raumtemperatur eingeschränkt. Diese resultiert aus einer inhomogenen Verformung, die in schmalen Scherbändern konzentriert ist. Die unzureichende Duktilität kann durch das Einbringen einer zweiten, duktilen Phase in die Glas-Matrix verbessert werden, so dass Komposite gebildet werden. Diese Komposite weisen in der Regel immer noch hohe Festigkeiten auf, lassen sich aber gleichzeitig deutlich besser plastisch verformen. Es wurden bereits verschiedene Arten von massiven metallischen Glas-Matrix-Kompositen entwickelt. Jedoch konnte die plastische Verformbarkeit in Zug- oder Biegeversuchen nur in den Materialien erhöht werden, in denen sich die zweite Phase bei der Erstarrung ausscheidet. Unter diesen in-situ Kompositen konnte eine signifikante Duktilität lediglich für zwei Legierungstypen beobachtet werden: massive metallische Gläser auf TiZrBe- und auf CuZr-Basis. Die Ausscheidungen der kubischen β-(Ti,Zr) Phase wachsen dendritenartig in die Glas-Matrix, wohingegen sich in letzterem Legierungstypen sphärische Ausscheidungen der Formgedächtnislegierung, B2-CuZr, im Glas bilden. CuZr-Basislegierungen haben dabei den großen Vorteil, dass sie kein Be enthalten, welches toxisch ist. Außerdem weisen diese Komposite auch dank der Formgedächtnisphase eine starke Kaltverfestigung auf. Das Konzept, massive metallische Formgedächtnis-Glas-Matrix-Komposite herzustellen, um die mechanischen Eigenschaften zu optimieren, wurde bisher nur auf CuZr-Basislegierungen angewandt. Es soll mittels dieser Arbeit nun erforscht werden, ob dieses Konzept auf andere massive metallische Gläser übertragbar ist. Des Weiteren ist der Zusammenhang zwischen Gefüge, Phasenbildung und mechanischen Eigenschaften der Komposite noch nicht vollständig verstanden, insbesondere die Rolle der Ausscheidungen in Bezug auf die Scherbandbildung und die Spannungsverteilung in der Glas-Matrix. Das Ziel der vorliegenden Arbeit ist die Entwicklung einer neuen Klasse massiver, metallischer Formgedächtnis-Glas-Matrix Komposite um das Konzept, welches ursprünglich für CuZr-Basislegierungen entwickelt wurde, zu erweitern. Die thermischen und mechanischen Eigenschaften sollen mit dem Gefüge und der Phasenbildung in Beziehung gesetzt werden, um so die fundamentalen Verformungsmechanismen und ihre Ursachen besser zu verstehen. Der Ausgangspunkt bei der Herstellung neuer massiver metallischer Formgedächtnis-Glas-Matrix Komposite ist das pseudobinäre TiCu-TiNi-System. In diesem System konnten massive Glasproben mit einem kritischen Gießdurchmesser von circa 1 mm hergestellt werden und zwar in dem Zusammensezungsbereich, in dem die kubische Formgedächtnisphase, B2-TiNi, gebildet wird. Während der Abkühlung findet in diesen Kompositen bei etwa 325 K eine martensitische Umwandlung der B2-Phase zur orthorhombischen B19-TiNi Phase statt. B2- und B19-TiNi weisen eine gute Verformbarkeit von bis zu 30% bei Raumtemperatur unter Zugbelastung auf. Die hier erzeugten Ti-Cu, Ti-Cu-Ni, Ti-Cu-Ni-Zr, Ti-Cu-Ni-Zr-(Si) und Ti-Cu-Ni-Co-Legierungen basieren auf Literaturangaben und Vorhersagen bezüglich der Glasbildungsfähigkeit in diesen Systemen mittels λ+Δh1/2-Kriterium, welches die Auswirkungen der Atomgrößenunterschiede der Elemente und deren elektronische Wechselwirkung einbezieht. Die Proben wurden im Schmelzspinnverfahren (Bänder) und mittels Saugguss in einer Cu-Kokille (Stäbe und Bleche) hergestellt. Die Weiter- und Neuentwicklung von Legierungen, beginnt mit dem Ti-Cu-System. Die Glasbildungsfähigkeit in diesem binären System ist nur gering, so dass lediglich mikrometerdicke amorphe Bänder hergestellt werden können. Die Ergebnisse zeigen, dass der beste Glasbildner eine Zusammensetzung von etwa Ti50Cu50 hat. Die Glasbildungsfähigkeit von binären Legierungen kann durch die Zugabe von Ni weiter verbessert werden. Dies führte innerhalb dieser Arbeit zur Entwicklung neuer Ti-Cu-Ni Formgedächtnis-Glas-Matrix Komposite, in welchen die orthorhombische Martensitphase in der Glas-Matrix ausgeschieden wird. Diese ternären Legierungen zeigen eine hohe Zugfestigkeit in Kombination mit einer hohen Bruchdehnung. Beim Überschreiten einer Temperatur von etwa 320 K vollziehen die Ausscheidungen eine reversible martensitische Umwandlung vom B19- zum B2-Strukturtyp. Durch die amorphe Matrix wird die Hochtemperaturphase (B2 Phase) stabilisiert. Dies verursacht unterschiedliche Umwandlungstemperaturen im Kompositmaterial, die davon abhängig sind, ob die Ausscheidungen nur teilweise oder vollständig in der Matrix eingebettet sind. Die Verformung beginnt in der weichen kristallinen Phase, welche eine heterogene Spannungsverteilung in der Glas-Matrix erzeugt und eine hohe Dichte an Scherbändern in der Matrix verursacht. Die Ausscheidungen haben zudem die Funktion, die Ausbreitung der Scherbänder zu blockieren und das Versagen des Materials zu verzögern. Die Größe der Komposite ist jedoch auf Grund der geringen Glasbildungsfähigkeit auf einen Stabdurchmesser von ca. 1 mm begrenzt. Dies kann mit dem Zulegieren von CuZr verbessert werden. Es wurden hier auf diese Weise neue Ti-Cu-Ni-Zr Komposite entwickelt, deren Durchmesser zwischen 2 und 3 mm liegt. Diese bestehen hauptsächlich aus sphärischen Ausscheidungen der kubischen B2-(Ti,Zr)(Cu,Ni)- und der Glasphase. Die wechselseitige Beziehung zwischen der Streckgrenze und dem Volumenanteil der B2-Phase wurde im Detail untersucht. Für kristalline Volumenanteile kleiner als 30 Vol.-% folgt die Streckgrenze der Mischungsregel und für größere Volumenanteile dem „lasttragenden Modell“ (load bearing model). Die Bruchdehnung wird ebenfalls vom Volumenanteil der Phasen beeinflusst und zeigt ein Maximum bei etwa 30 Vol.-% an B2-Phase. Dies stimmt mit der Vorhersage des „Drei-Element-Modells“ überein. Es wurde festgestellt dass die kubische B2-Phase während der Verformung eine martensitische Umwandlung durchführt, was die starke Kaltverfestigung und die hohen Bruchspannungen dieser Legierungen zur Folge hat. Die Glasbildungsfähigkeit von TiCu-Basislegierungen kann im Gegenzug weiterhin durch geringe Si-Zusätze gesteigert werden. Hierbei tritt jeweils ein Maximum bei Zusätzen von 1 und 0,5 at-% Si zu binären Ti-Cu- oder zu quarternären Ti-Cu-Ni-Zr-Legierung auf. Das Optimum der Glasbildungsfähigkeit ist das Ergebnis sowohl eines geringeren Anteils hochschmelzender Ti5Si3-Ausscheidungen, die als Keimbildner für andere kristalline Phasen dienen, als auch der erhöhten Stabilität der Schmelze sowie der unterkühlten Schmelze. Der Zusatz von Co wiederum hat einen gegenteiligen Effekt. Er vermindert die Glasbildungsfähigkeit von Ti-Cu-Ni-Legierungen drastisch. Zudem scheinen sowohl die martensitische Umwandlungstemperatur als auch das mechanische Verhalten mit der Zahl und Konzentration der Valenzelektronen der B2-Phase zu korrelieren. Die Umwandlungstemperatur sinkt mit steigender Valenzelektronenkonzentration. Eine ausgezeichnete Kombination von hoher Streckgrenze und Bruchdehnung tritt für die Legierungen Ti-Cu-Ni-Zr und Ti-Cu-Ni-Zr-Si mit einem relativ geringen CuZr-Anteil auf. Die Bruchdehnung unter Druck ist fast zweimal höher als es für CuZr-Basis-Komposite gewöhnlich beobachtet worden ist. Die Legierung Ti45Cu39Ni11Zr5 zeigt beispielsweise eine Streckgrenze von 1490±50 MPa in Kombination mit einer plastischen Dehnung von 23,7±0,5%. Für die CuZr-reicheren Ti-Cu-Ni-Zr Zusammensetzungen wurde jedoch eine geringere Duktilität festgestellt, was das Resultat spröder Cu2TiZr-Ausscheidungen in der Glas-Matrix ist. Die vorliegende Arbeit erweitert folglich das Konzept der „Formgedächtnis-Glas-Matrix Komposite“, welches bisher auf CuZr-basierte Legierungen beschränkt war und liefert wichtige Einblicke in die Beziehung zwischen Phasenbildung und mechanischen Eigenschaften der neuen Klasse hochfester TiCu-Basislegierungen, welche nach weiterer Optimierung vielversprechend sein könnten für Hochleistungsanwendungen wie Durchflussmesser, Sensoren und mikrometer- und mm-große Antriebe

Thesis (Ph. D.)--Materials Science and Engineering, Georgia Institute of Technology, 2008.
Committee Chair: Thadhani, Naresh; Committee Member: Doyoyo, Mulalo; Committee Member: Kecskes, Laszlo; Committee Member: Li, Mo; Committee Member: Sanders, Thomas; Committee Member: Zhou, Min.

Récemment, la réduction de taille des dispositifs implantés est devenue une tendance majeure de l’implantologie dentaire moderne. Cependant, elle nécessite le développement de matériaux présentant de fortes résistances mécaniques. Le titane et ses alliages, matériaux dentaires de référence, semblent avoir atteint un plateau en termes de propriétés mécaniques, ce qui peut limiter leur utilisation pour une telle stratégie. Les alliages métalliques amorphes à base de titane constituent une classe unique de matériaux présentant de fortes limites d’élasticité qui en font des candidats potentiels pour la réalisation de pièces implantables de petit diamètre. Nous assistons aussi à un intérêt croissant pour les implants en céramiques. La couleur blanche de la zircone yttriée (Y-TZP), combinée à sa capacité unique de résistance par transformation de phase en ont fait un matériau de choix pour la réalisation d’implant dentaires plus esthétiques. Cependant, la zircone yttriée peut être sensible à un mécanisme de dégradation à basse température en milieu aqueux, qui a pu susciter certaines inquiétudes. De plus, même si elle est plus résistante que la plupart des autres céramiques, elle reste un matériau élastique-fragile, sans plasticité, et donc sensible à la présence de défauts. Différentes céramiques dopées à l’oxyde de cérium (Ce-TZP) ont été développées au cours des dernières années et certains de ces matériaux ont montré une ténacité considérable et une plasticité de transformation significative comparées aux céramiques conventionnelles. Cette combinaison de propriétés en fait des candidats potentiels pour la réalisation d’implants dentaires esthétiques, comme alternatives crédibles à la 3Y-TZP. Durant ce travail de thèse, le potentiel de ces deux matériaux, pour deux applications différentes a été étudié. La première application concerne la réalisation d’implants dentaires mini-invasifs en remplacement du titane. La seconde application est centrée sur la réalisation de nouveaux implants esthétiques en céramique, plus tenaces et plus fiables, en remplacement de la 3Y-TZP. La première partie de ce travail sera axée sur le verre métallique Ti40Zr10Cu36Pd14. Le potentiel de ce verre métallique pour la fabrication de futurs implants mini-invasifs sera démontré et sa plus-value en termes de résistance à la fatigue comparé aux titanes biomédicaux conventionnels sera mise en évidence. Le rôle des éléments d’alliage tels que l’étain et le silicium sur les propriétés globales de l’alliage, telles que la cytocompatibilité et la résistance à la corrosion, sera également analysé. La deuxième partie de ce travail portera sur un nouveau composite à base de Ce-TZP. La résistance mécanique de ce matériau sera évaluée et comparée à la 3Y-TZP. De plus, sa plasticité de transformation unique et ses conséquences sur le comportement mécanique de ce matériau seront approfondies et décrites à l’aide d’expériences originales
Recently, dental implant downsizing has become one major trend in modern implantology but it requires the development of materials with improved mechanical resistance. Never- theless, titanium and its alloys, the gold standard dental materials, seem to have reached a plateau in terms of mechanical properties, which may limit their use for such strategy. Amorphous titanium-based metallic alloys are a unique class of materials showing high mechanical and fatigue properties, good corrosion resistance and a relatively low Young’s modulus, which thus make them potential candidates for the realization of such-small diameter implantable pieces in substitution to polycrystalline titanium. There is also a growing trend to use ceramic implants in dentistry. In particular, the white color of Yttria-Tetragonal Zirconia Polycrystal (Y-TZP) materials combined with their unique transformation toughening ability have made them materials of choice for the realization of metal-free, aesthetic dental implants. However, ageing of Y-TZP ceramics in aqueous environments may be a concern and even if strongest than many other ceramics, Y-TZPs still remain elastic-fragile with a sensitivity to the presence of defects. Various Ceria-doped based zirconia ceramics have been developed over the past years, in particular during two recent European projects led by MATEIS and Anthogyr. These materials may be highly resistant to flaws with a considerable toughness and an unusual transformation- induced ductility. This unique combination of properties makes them potential candidates for the realization of ceramic dental implants, as an alternative to 3Y-TZP. Within this PhD work, the potential of the two materials for (i) the realization of less invasive implants to replace titanium alloys on one hand, and (ii) aesthetic and more reliable ceramic implants as alternative to 3Y-TZP on the other hand, will be studied. The first part of this work will be focused on Ti40Zr10Cu36Pd14 metallic glass. The potential of this amorphous alloy for future implantable devices fabrication is assessed in terms of ion release in relevant media, corrosion resistance, biocompatibility and fatigue resistance, with a comparison to the benchmark conventional biomedical grade Ti alloys. The role of Sn and Si alloying elements on the overall properties of the alloy will be also analyzed. The second part of this work will deal with a new Ce-TZP based composite. Mechan- ical characterization and fatigue resistance will be evaluated and compared to 3Y-TZP material. Furthermore, the transformation-induced plasticity of this composite will be better understood, thanks to original experiments, in order to validate its reliability and its absence of potential damage under stress. All the results may open new perspectives in the future of dental applications

Lack of crystalline order and microstructural features such as grain/grain-boundary in metallic glasses results in a suite of remarkable attributes including very high strength, close to theoretical elasticity, high corrosion and wear resistance, and soft magnetic properties. By altering the morphology and tuning of composition, MGs may be transformed into high-performance catalytic materials. In this study, the catalytic properties of metallic glass powders were demonstrated in dissociating toxic organic chemicals such as AZO dye. BMG powders showed superior performance compared to state of the art crystalline iron because of their high catalytic activity, durability, and reusability. To enhance the catalytic properties, high energy mechanical milling was performed to increase the surface area and defect density. Iron-based bulk metallic glass (BMG) of composition Fe48Cr15Mo14Y2C15B6 was used because of its low cost and ability to make large surface area by high energy ball milling. AZO dye was degraded in less than 20 minutes for the 9 hours milled Fe-BMG. However, subsequent increase in ball milling time resulted in devitrification and loss of catalytic activity as measured using UV-Visible spectroscopy. Aluminum-based bulk metallic glass (Al-BMG) powder of composition Al82Fe3Ni8Y7 was synthesized by arc-melting the constituent elements followed by gas-atomization. The particle size and morphology were similar to Fe-BMG with a fully amorphous structure. A small percentage of transition metal constituents (Fe and Ni) in a mostly aluminum alloy showed high catalytic activity, with no toxic by-products and no change in surface characteristics. Al-alloy particles, being light-weight, were easily dispersed in aqueous medium and accelerated the redox reactions. The mechanism of dye dissociation was studied using Raman and Infrared (IR) spectroscopy. Breaking of -C-H- and - C-N- bonds of AZO dye was found to be the primary mechanism. Mechanical behavior of individual BMG particles was evaluated by in situ pico-indentation in a scanning electron microscope (SEM) to understand the fracture mechanisms. Catastrophic shear banding was found to be the primary fracture mode, which supported the observation of flake formation during high energy ball milling.

In this thesis two series of alloys were developed to obtain a combination of high strength, high ductility and work hardening. A new composition design strategy was proposed to create bulk metallic glass composites (BMGC) with high strength, large ductility and excellent work hardening from the brittle MgZnCa bulk metallic glass system. The volume fraction, size of both the dendrites and amorphous matrix can be effectively tuned by varying of the composition, and the yield strength, fracture strength and ductility also varies accordingly. The increase in alloying elements results in an increase in the volume fraction of amorphous matrix and a decrease in the dendrite size, which leads to higher yielding strength but lower ductility. The mechanical properties of the current Mg alloy can be interpreted by considering the BMGCs as a combination of the nanometer scale metallic glass matrix with a ductile dendritic structure. The high strength, large ductility and excellent work hardening observed in the Mg_(91.5 ) Zn_(7.5 ) Ca_1 can be attributed to the homogeneous deformation of nanometre scale amorphous matrices, which delays the formation and rapid propagation of microcracks from the interface. In addition, a series of in-situ-cast nanostructured CuZrTi alloys were successfully designed by appropriate choice of alloying elements and compositions. XRD and TEM analysis shows that the alloys consist of softer Cu solid solution and harder nano-scale Cu_51 Zr_(14 )matrix embedded with retained Cu_5 Zr_ .The Cu_90.5 Zr_(7.5 ) Ti_2alloy exhibited a yield strength of 787MPa, a fracture strength of 1221MPa and room temperature uniform tensile elongation of 5.16%, exhibiting simultaneous ultrahigh strength and large uniform elongation. During tensile tests, the relatively softer (larger) primary Cu dendrites with numerous intragranular nanoprecipiates are believed to yield first, leading to substantial dislocation accumulation due to their relatively large grain size and the uniform distribution of numerous intragranular nanoprecipiates. With further increase in loading, the ultrafine Cu solid solution in the ultrafine clusters starts yielding and dislocation multiplication commences in this ultrafine Cu. Meanwhile, the formation of deformation bands are believed to start in the primary Cu dendrites due to the already existing high dislocation density, both of which further contribute to the work hardening and uniform plastic deformation. Finally, the hard Cu_51 Zr_(14 ) matrix commences plastic deformation and upon further loading, cracks start to form from the interface, leading to the final failure.

Bulk metallic glasses and multi-principal element alloys represent relatively new classes of multi-component engineering materials designed for satisfying multiple functionalities simultaneously. Correlating the microstructure with mechanical behavior (at the microstructural length-scales) in these materials is key to understanding their performance. In this study, the structure evolution and nano-mechanical behavior of these two classes of materials was investigated with the objective of fundamental scientific understanding of their properties. The structure evolution, high temperature nano-mechanical behavior, and creep of two Zr-based alloys was studied: Zr41.2Ti13.8Cu12.5Ni10.0Be22 (Vitreloy1) and Zr52.5Ti5Cu17.9Ni14.6All0 (Vitreloy105). Devitrification was found to proceed via the formation of a metastable icosahedral phase with five-fold symmetry. The deformation mechanism changes from inhomogeneous or serrated flow to homogenous flow near 0.9Tg, where Tg is the glass transition temperature. The creep activation energy for Vitreloy1 and Vitreloy105 were 144 kJ/mol and 125 kJ/mol, respectively in the range of room temperature to 0.75Tg. The apparent activation energy increased drastically to 192 kJ/mol for Vitreloy1 and 215 kJ/mol for Vitreloy105 in the range of 0.9Tg to Tg, indicating a change in creep mechanism. Structure evolution in catalytic amorphous alloys, Pt57.5Cu14.7Ni5.3P22.5 and Pd43Cu27Ni10P20, was studied using 3D atom probe tomography and elemental segregation between different phases and the interface characteristics were identified. The structure evolution of three multi-principal element alloys were investigated namely CoCrNi, CoCrFeMnNi, and Al0.1CoCrFeNi. All three alloys formed a single-phase FCC structure in as-cast, cold worked and recrystallized state. No secondary phases precipitated after prolonged heat treatment or mechanical working. The multi-principal element alloys showed less strain gradient plasticity compared to pure metals like Ni during nano-indentation. This was attributed to the highly distorted lattice which resulted in lesser density of geometrically necessary dislocations (GNDs). Dislocation nucleation was studied by low load indentation along with the evaluation of activation volume and activation energy. This was done using a statistical approach of analyzing the "pop-in" load marking incipient plasticity. The strain rate sensitivity of nanocrystalline Al0.1CoCrFeNi alloy was determined by in situ compression of nano-pillars in a Pico-indenter. The nanocrystalline alloy demonstrated a yield strength of ~ 2.4 GPa, ten times greater than its coarse grained counterpart. The nanocrystalline alloy exhibited high strain rate sensitivity index of 0.043 and activation volume of 5b3 suggesting grain boundary dislocation nucleation.

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.

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. This report discusses two aspects of research on bulk metallic glasses. The first is an effort to increase their toughness by combining them with reinforcement to form a composite. The second is the first direct measurement of plane strain fracture toughness of bulk metallic glass. Particulate and continuous fiber reinforced composite materials were fabricated using bulk metallic glass as the matrix. The particulate composites combined W, WC, SiC and Ta reinforcements in a matrix with the composition Zr57Nb5Al10Cu15.4Ni12.6. Continuous fiber composites were fabricated using W and 1080 carbon steel (music) wire reinforcement in a Zr41.25Ti13.75Cu12.5Ni10Be22.5 matrix. In both cases the metallic glass remained amorphous during processing. Compressive strain to failure was greatly enhanced in both particulate and continuous fiber composites by the formation of multiple shear bands. Tungsten reinforcement provided the greatest improvement. The tungsten is wet well by the metallic glass, and forms a strong interface. Both particulate and fiber reinforced composite showed improved tensile properties. Energy (per unit volume) to break increased 52% for 5% Vf, 150 [...] W reinforced Zr57Nb5Al10Cu15.4Ni12.6 and 18% for 60% Vf music wire reinforced Zr41.25Ti13.75Cu12.5Ni10Be22.5. Tightly bonded ductile particles and weakly bonded continuous fibers proved best for enhancing the tensile properties of bulk metallic glass. Fracture toughness of the unreinforced Zr41.25Ti13.75Cu12.5Ni10Be22.5 bulk metallic glass was determined using 3-point bend measurements and coherent gradient sensing (CGS). The measured fracture toughness is nominally 55 [...]. Once initiated, cracks in the unreinforced metallic glass propagated in an unstable manner. Continuous fiber reinforcement was demonstrated to arrest crack propagation in 3-point bend fracture tests of bulk metallic glass matrix composites.

We have studied the mechanical properties of monolithic bulk metallic glasses and composite in the La based alloys. La₈₆₋yAl₁₄(Cu, Ni)y (y=24 to 32) alloy systems was used to cast the in-situ structure and subsequently tested under compression. We found that the ductility of the monolithic is actually poorer than that of the fully crystalline composite.
Singapore-MIT Alliance (SMA)

碩士
義守大學
材料科學與工程學系碩士班
98
The base alloy in this study is Mg58Cu29.5Y6Nd5Ag1.5 bulk metallic glass (BMG) rods were made by the injection casting method. The Ti particles (10、20 and 30vol.%) were selected to be the additive in the base material to form the bulk metallic glass composites (BMGCs). Ti powder was spherical with bimodal size in the range of 75~105μm and 45μm. The thermal stability and the microstructure characterizations of the resulting materials were performed by DSC、XRD and SEM. Vickers indentation and compression test were performed to estimate the mechanical properties of alloys. The results indicated that GFA and thermal stability of Mg-based BMGCs decreased with increasing the content of Ti particles, but the glassy state of the matrix was maintained even in the coexistence with Ti powders. The fracture toughness and the ultimate strength of Mg-based BMGCs increased to 31MPa m1/2 and 963MPa, respectively. Besides, an improvement of compressive strain to ~7% of the Mg-based BMGCs with the addition of 30vol.% Ti particles. Moreover, SEM observations of Mg58Cu29.5Y6Nd5Ag1.5 with 30vol.% Ti powders showed that the propagation of shear bands could be stopped or branched by the dispersion of Ti particles with large size of 75~105μm and large sized vein patterns were formed upon the fracture surface. Although the small size Ti particles (45μm) could not stopped the shear bands motion, small size of vein patterns were formed in the interspacing of small Ti particles. The resulting Mg-based BMGCs with adding Ti particles in this study exhibit high glass forming ability (GFA) and excellent compressive properties.

碩士
國立中央大學
機械工程研究所
100
Due to technology advancements, the medical treatment is being improved. One of being concerned is the attempt to simplify the procedure of implantation surgery, which possibly relieves the pain during the recovering process. The biodegradable material provides an attractive solution which is decomposable in human body with widely attention for decades. MgZnCa bulk metallic glass alloy, which has good mechanical properties, biocompatibility and uniform biodegradability, is suitable for the application in orthopedic implants, for example, the bone screws and bone plates. Unfortunately, such material is quite brittle where further application is limited. In this study, we have successfully synthesized the Ti particles reinforced Mg60Zn35Ca5 bulk metallic glass composites (BMGCs) rod with diameter of 2 mm by injection casting method in an argon atmosphere. The glass forming ability (GFA) and the mechanical properties of these Mg-based BMGCs have been systematically investigated as a function of the volume fraction (Vf) of Ti particles. The results showed that the compressive ductility increased with Vf of Ti particles. The mechanical performance with up to 5.4% compressive failure strain and 1187 MPa fracture strength at room temperature can be obtained for the Mg-based BMGCs with 50 vol.% Ti particles, which suggests that these dispersed Ti particles can absorb the energy of crack and branches the primary crack into multiple secondary crack. Therefore, further propagation of crack is blocked and then enhances the plasticity.

碩士
義守大學
材料科學與工程學系碩士班
97
The base alloys of Mg58Cu31Y6Nd5 bulk metallic glass (BMG) rods (~4 mm in diameter) with high glass forming ability (GFA) and high thermal properties are made by injection casting. Vickers indentation and compression test are performed for the mechanical properties measuring. It exhibits that the fracture toughness of the base alloy is ~8MPa m1/2 and the fracture behavior is brittle. For the mechanical properties promotion, the Fe particles (10, 20, 30 vol%) are selected to be the additive in the base alloy. Then the microstructure characterizations of the resulting BMG compositions are performed by XRD and SEM analyses. No detrimental effect of the additive Fe particles is observed on the glass forming ability of the base alloys. Besides, the result of the compressive test of the Mg58Cu31Y6Nd5-Feamorphous composite alloys reveals that the plastic strain is improved with the addition of Fe particles (εp~23%) and the spread vein-patterns are formed on the fracture surface. The fracture toughness is also improved. KIC of the Mg58Cu31Y6Nd5 with 30 vol% Fe is ~27 MPa m1/2. SEM observation of BMG composites reveals that the shear bands and the cracks propagation are impeded by the Fe particles and the secondary shear bands are formed during the plastic deformation process. It indicated that the addition of Fe particles for plasticity improvement of the Mg58Cu31Y6Nd5 alloy is contributive.

碩士
義守大學
材料科學與工程學系碩士班
96
Mg-based bulk metallic glasses have high glass-forming ability, specific strength, and strength, e.g., 2-3 times higher for Mg-based metallic glasses than that of corresponding crystalline Mg-based alloys. However, their application is limited up to now because of the inherent low stiffness/workability and ineffective plastic deformation. In this study, one added the ductile Mo particles into Mg-Cu-Y-Gd(Nd ) base BMGs for improving the ductility of alloys. Thermal and mechanical properties of BMGs are evaluated. It has been found that the glass forming ability, the viscosity and the porous ratio of BMGs decreased with increasing Mo content into Mg58Cu31Y5Gd6 base BMG. In addition, the interface between Mg58Cu31Y5Gd6 matrix and Mo particles is incoherent. In comparison with Mg58Cu31Y5Gd6 base BMG, the Mo particles and Mg58Cu31Y6Nd5 base BMGs are more compatible. The results of compressive testing of Mg58Cu31Y6Nd5 base BMGs showed that no Mo particles are peeled off and the particles effectively impede shear band propagation and promote the initiation and branching of secondary shear bands. TEM analysis revealed that there are some Cu5Y crystallite observed between the interface of matrix alloy and Mo particle. The interface boundary between Cu5Y crystallite and Mo particle induced the stress concentration effect and it makes some Mo particles are peeled off during compressive testing. The same results are observed by SEM. The dispersion of Mo particles into the galssy matrix caused the increasing of the compressive plastic deformation. However, the improvement effects of plastic deformation are restrained because of the formation of Cu5Y crystallite.

碩士
義守大學
材料科學與工程學系碩士班
98
Cu-based bulk metallic glass is considered a good material for glass-forming ability because of its excellent properties. And High strength, high hardness, more than 2% of the elastic strain and wear resistance, and to attract the attention of the general public. The monolithic bulk metallic glass under compression load, usually caused by the glass transition temperature before it is highly uneven plastic deformation and then destroyed. However, the precipitation is have limit of In-situ, so this paper by suction-casting method, and above in-situ and ex-situ approach successfully obtained 2 ~ 4mm diameter and different components of bulk metallic glass composite material of the round bar. By DSC, XRD, SEM, TEM, Vickers hardness instrument of systematic analysis of (Zr48Cu36Al8Ag8)Si0.75 Ta adding different volume percentage of metal particles and (Zr48Cu32Al8Ag8Ta4)Si0.75 Ta adding different volume percentage of metal particles, The composition of the thermal properties and mechanical properties. Ex-situ (Ta) the ways in which the hardness values of about 522 ~ 559Hv between the yield strength to maintain 1615 ~ 1756MPa. Plastic deformation increases with the Ta content significantly increasing trend(But When the Ta content of 10vol%, the diameter of 2mm round bar up to 18% more than the (real) plastic deformation).Then use (Zr48Cu36Al8Ag8)Si0.75 integrated in-situ and ex-situ (Ta) obtained by way of the hardness of the alloy composition at about 522 ~ 543Hv.Ta precipitates show the overall hardness value was not obvious. And In the compression tests, each alloy the yield strength values range between 1741 ~ 1852MPa the other hand, plastic deformation increased with Ta content significantly rising, and when the Ta content of 9vol%, the diameter of 2mm round bar up to 40% more than the plastic deformation.

碩士
國立中央大學
機械工程學系
106
Suture anchors are often used to rivet the suture wires at the bones in orthopedic surgery. Therefore, suture anchor must be able to withstand the stress of biological movements and non-harmful to human body. This attracts the medical community to pay lots attention on the improvement of materials for suture anchor. We want that the material has the good mechanical properties of the material. The Mg-based bulk metallic glasses (BMG) produced by our laboratory has high strength and Young's modulus is similar to the value of human bones. Therefore, it is very suitable to apply the Mg-based metallic glass alloys on suture anchor. In this study, Mg66Zn29Ca5, has the best glass forming ability in the Mg-Zn-Ca metallic glass alloy system, was selected to be the base alloy. Then this base alloy was added with different vol% micro-sized spherical Fe and TiZr-based metallic glass particles to form Mg-based bulk metallic glass composite (BMGC), respectively for improving its fracture toughness. Due to the limitation of cooling rate, the BMGC rods with 4 mm in diameter only present partial metallic glass state, but still show much higher compressive strength of commercial magnesium alloy. Based on the results of this study, the Mg-based BMGCs added Fe particle could not obtain effective improvement on fracture toughness. On the other hand, the Mg-based BMGCs added with TiZr-based metallic glass particles present a clear improvement of fracture toughness. With increasing the addition of Ti-Zr metallic glass particles to 30 vol.%, the fracture toughness of Mg-based BMGC increases from 1.17 to 4.19 MPa‧m1/2 and remains the maximum compressive strength of 535 MPa.

碩士
國立中央大學
材料科學與工程研究所
104
In order to improve the mechanical properties as well as corrosion resistance of Mg-based metallic glass (BMG) and Mg-based metallic glass composite (BMGC). The Zr-based metallic glass thin film (MGTF) of 200 nm thickness was coated on the Mg-based BMGC with two different buffer layers, Al-Ti (25 nm/25 nm) and Cu(50 nm), for adhesion ability investigation. The BMGC plates (with dimension of 4 mm W x 3 mm T x 35 mm L) of Mg58Cu31Gd11 with 25 vol.% Mo particles (size of 25 m) [2] was selected as the substrate and coated with 200 nm Zr-based ((Zr53Cu30Ni9Al8)99.5Si0.5) MGTF by DC-sputtering. The results of 3-point bending test show that the flexural strength of the Mg-based BMGC (180 MPa) can be significantly enhanced to 254 MPa for the Mg-based BMGC with 200 nm Zr-based MGTF coating. The remarkable increase in flexural strength of the Mg-based BMGC coated with Zr-based MGTF is suggested that the Zr-based MGTF can smooth the surface (by covering the defects on the specimen surface) to prevent the stress concentration and also provide residual stress to suppress the crack initiation from the specimen surface during bending test. In addition, the results of polarization electrochemical test reveal that the Zr-based MGTF exhibits much better corrosion resistance in 0.9 wt. % sodium chloride solution. Accordingly, the coating of 200 nm Zr-based MGTF on the Mg-based BMGC by sputtering is believed a promising method to protect the Mg-based BMGC from the island environment.

碩士
義守大學
材料科學與工程學系碩士班
97
Mg-based bulk metallic glass exhibit excellent compressive properties, large supercooled liquid region and high glass forming ability(GFA). According to previous reasearch, the excellent thermal properties may attribute to the coaction of Mg-Cu-Y and Mg-Cu-Y-Gd alloy systems with silver addition. Therefore, in the present study, we systematically investigated the effect of partial substitution of Cu by Ag on the thermal properties of Mg-Cu-Y-Nd alloys in wide compositional range. In order to improve ductility of Mg-based bulk metallic glass simultaneously, we prepare a BMG matrix composite with micrometer-sized Molybdenum particles addition as a kind of reinforcement in Mg-Cu-Y-Nd-Ag alloy with best GFA. The results indicated that the GFA and thermal stability are best with adding Ag content in Mg-Cu-Y-Nd alloy, but it decreased with increasing of Molybdenum particles addition. It can also observed the nanocrystals(CuY) precipitate around interface between matrix and Molybdenum particles by transition electron microscopy(TEM). General speaking, brittle nanocrystals can speed-up the shear bands or cracks propagation even through they act as obstacles. But the interface between CuY nanocrystals and Molybdenum particles are coherent in Mg-Cu-Y-Nd alloy. Molybdenum particles can form multiple shear bands uniformly and stabilize crack growth which prevent catastrophic failure. The resulting Mo/Mg-Cu-Y-Nd-Ag BMGCs not only show high plastic strain (~29%)in uniaxial compression, but also enhance fracture toughness with 63 MPa•m1/2.

The large elastic limit, the strength close to the theoretical limit, the excellent magnetic properties and good corrosion resistance of bulk metallic glasses (BMGs) make them promising for several applications such as micro-geared motor parts, pressure sensors, Coriolis flow meters, power inductors and coating materials. The main limitation of these materials is their reduced macroscopic ductility at room temperature, resulting from an inhomogeneous deformation concentrated in narrows shear bands. The poor ductility can be overcome by the incorporation of a ductile second phase in the glassy matrix to form composites, which exhibit a better balance between strength and ductility. Different types of BMG composites have been developed to date but considerable plastic strain during tensile or bending tests has been only obtained for composites with in-situ formation of the second phase during solidification. Among these in-situ formed composites, significant tensile ductility has been only observed for two types of alloys so far: TiZrBe-based and CuZr-based BMG composites. The former precipitate dendrites of the cubic β-(Ti,Zr) phase in the glass matrix, whereas the latter combine spherical precipitates of the cubic B2-CuZr shape memory phase within the glass. The CuZr-based BMG composites have certain advantages over the TiZrBe-based composites such as the absence of Be, which is a toxic element, and exhibit a strong work-hardening behaviour linked to the presence of the shape memory phase. This concept of “shape memory” BMG composites has been only applied to CuZr-based alloys so far. It is worth investigating if such a concept can be also used to enhance the plasticity of other BMGs. Additionally, the correlation between microstructure, phase formation and mechanical properties of these composites is still not fully understood, especially the role of the precipitates regarding shear band multiplication as well as the stress distribution in the glassy matrix, which should be significantly influenced by the precipitates. The aim of the present work is to develop a new family of shape memory bulk metallic glass composites in order to extend the concept initially developed for CuZr-based alloys. Their thermal and mechanical properties shall be correlated with the microstructure and phase formation in order to gain a deeper understanding of the fundamental deformation mechanisms and thermal behaviour. A candidate to form new shape memory BMG composites is the pseudo-binary TiCu-TiNi system because bulk glassy samples with a critical casting thickness of around 1 mm have been obtained in the compositional region where the cubic shape memory phase, B2-TiNi, precipitates. This phase undergoes a martensitic transformation to the orthorhombic B19-TiNi during cooling at around 325 K. The B2- and B19-TiNi exhibit an extensive deformation at room temperature up to 30% during tensile loading. Compositions in the Ti-Cu, Ti-Cu-Ni, Ti-Cu-Ni-Zr, Ti-Cu-Ni-Zr-(Si) and Ti-Cu-Ni-Co systems were selected based on literature data and on a recently proposed λ+Δh1/2 criterion, which considers the effect of atomic size mismatch between the elements and their electronic interaction. Samples were then produced by melt spinning (ribbons) and Cu-mould suction casting (rods and plates). The investigation started in the Ti-Cu system. A low glass-forming ability (GFA) was observed with formation of amorphous phase only in micrometer-thick ribbons and the results showed that the best glass former is located around Ti50Cu50. Considering that the GFA of the binary alloys can be further improved with additions of Ni, new Ti-Cu-Ni shape memory BMG composites were then developed in which the orthorhombic Ti(Ni,Cu) martensite precipitates in the glassy matrix. These alloys exhibit a high yield strength combined with large fracture strain and the precipitates show a reversible martensitic transformation from B19 to B2-type structure at a critical temperature around 320 K (during heating). The amorphous matrix stabilizes the high-temperature phase (B2 phase), which causes different transformation temperatures depending on whether the precipitates are partially or completely embedded in the glassy matrix. The deformation starts in the softer, crystalline phase, which generates a heterogeneous stress distribution in the glassy matrix and causes the formation of multiple shear bands. The precipitates also have the important function to block the fast movement of shear bands and hence retard fracture. However, the size of such composites is limited to 1 mm diameter rods because of their low GFA, which can be further improved by adding CuZr. New Ti-Cu-Ni-Zr composites with diameter ranging from 2 to 3 mm were developed, which consist mainly of spherical precipitates of the cubic B2-(Ti,Zr)(Cu,Ni) and the glassy phase. The interrelation between composite strength and volume fraction of B2 phase was analysed in detail, which follows the rule of mixture for values lower than 30 vol.% or the load-bearing model for higher values. The fracture strain is also affected by the volume fraction of the respective phases with a maximum observed around 30 vol.% of B2 phase, which agrees with the prediction given by the three-body element model. It was observed that the cubic B2 phase undergoes a martensitic transformation during deformation, resulting in a strong work hardening and a high fracture stress of these alloys. The GFA of the Ti-Cu -based alloys can be further increased by minor additions of Si. A maximum GFA is observed for additions of 1 and 0.5 at.% Si to binary Ti-Cu or quaternary Ti-Cu-Ni-Zr alloys, respectively. This optimum GFA results from the formation of a lower amount of highly stable Ti5Si3 precipitates, which act as nuclei for other crystalline phases, and the increased stability of the liquid and the supercooled liquid. The addition of Co has the opposite effect. It drastically decreases the GFA of Ti-Cu-Ni alloys and both the martensitic transformation temperature and their mechanical behaviour seem to correlate with the number and concentration of valence electrons of the B2 phase. The transformation temperature decreases by increasing the concentration of valence electrons. An excellent combination of high yield strength and large fracture strain occurs for Ti-Cu-Ni-Zr and Ti-Cu-Ni-Zr-Si alloys with a relatively low amount of CuZr, with a fracture strain in compression almost two times larger than the one usually observed for CuZr-based composites. For instance, the Ti45Cu39Ni11Zr5 alloy exhibit a yield strength of 1490±50 MPa combined with 23.7±0.5% of plastic strain. However, a reduced ductility was found for the CuZr-richer Ti-Cu-Ni-Zr compositions, which results from the precipitation of the brittle Cu2TiZr phase in the glassy matrix. The present study extends the concept of “shape memory BMG matrix composites” originally developed for CuZr-based alloys and delivers important insights into the correlation between phase formation and mechanical properties of this new family of high-strength TiCu-based alloys, which upon further optimization might be promising candidates for high-performance applications such as flow meters, sensors and micro- and mm-sized gears.
Auf Grund der hohen Elastizitätsgrenze, Festigkeiten, die nahe an der theoretischen Grenze liegen, sehr guten magnetischen Eigenschaften, sowie einer guten Korrosionsbeständigkeit erscheint der Einsatz massiver metallischer Gläser (BMG) vielversprechend in zahlreichen Gebieten, wie z.B. in Mikro-Getriebemotorteilen, Coriolis-Massendurchflussmessern, Drucksensoren, Speicherdrosseln und als Beschichtungsmaterialien. Der Einsatz dieser Materialien wird jedoch hauptsächlich durch ihre begrenzte makroskopische Duktilität bei Raumtemperatur eingeschränkt. Diese resultiert aus einer inhomogenen Verformung, die in schmalen Scherbändern konzentriert ist. Die unzureichende Duktilität kann durch das Einbringen einer zweiten, duktilen Phase in die Glas-Matrix verbessert werden, so dass Komposite gebildet werden. Diese Komposite weisen in der Regel immer noch hohe Festigkeiten auf, lassen sich aber gleichzeitig deutlich besser plastisch verformen. Es wurden bereits verschiedene Arten von massiven metallischen Glas-Matrix-Kompositen entwickelt. Jedoch konnte die plastische Verformbarkeit in Zug- oder Biegeversuchen nur in den Materialien erhöht werden, in denen sich die zweite Phase bei der Erstarrung ausscheidet. Unter diesen in-situ Kompositen konnte eine signifikante Duktilität lediglich für zwei Legierungstypen beobachtet werden: massive metallische Gläser auf TiZrBe- und auf CuZr-Basis. Die Ausscheidungen der kubischen β-(Ti,Zr) Phase wachsen dendritenartig in die Glas-Matrix, wohingegen sich in letzterem Legierungstypen sphärische Ausscheidungen der Formgedächtnislegierung, B2-CuZr, im Glas bilden. CuZr-Basislegierungen haben dabei den großen Vorteil, dass sie kein Be enthalten, welches toxisch ist. Außerdem weisen diese Komposite auch dank der Formgedächtnisphase eine starke Kaltverfestigung auf. Das Konzept, massive metallische Formgedächtnis-Glas-Matrix-Komposite herzustellen, um die mechanischen Eigenschaften zu optimieren, wurde bisher nur auf CuZr-Basislegierungen angewandt. Es soll mittels dieser Arbeit nun erforscht werden, ob dieses Konzept auf andere massive metallische Gläser übertragbar ist. Des Weiteren ist der Zusammenhang zwischen Gefüge, Phasenbildung und mechanischen Eigenschaften der Komposite noch nicht vollständig verstanden, insbesondere die Rolle der Ausscheidungen in Bezug auf die Scherbandbildung und die Spannungsverteilung in der Glas-Matrix. Das Ziel der vorliegenden Arbeit ist die Entwicklung einer neuen Klasse massiver, metallischer Formgedächtnis-Glas-Matrix Komposite um das Konzept, welches ursprünglich für CuZr-Basislegierungen entwickelt wurde, zu erweitern. Die thermischen und mechanischen Eigenschaften sollen mit dem Gefüge und der Phasenbildung in Beziehung gesetzt werden, um so die fundamentalen Verformungsmechanismen und ihre Ursachen besser zu verstehen. Der Ausgangspunkt bei der Herstellung neuer massiver metallischer Formgedächtnis-Glas-Matrix Komposite ist das pseudobinäre TiCu-TiNi-System. In diesem System konnten massive Glasproben mit einem kritischen Gießdurchmesser von circa 1 mm hergestellt werden und zwar in dem Zusammensezungsbereich, in dem die kubische Formgedächtnisphase, B2-TiNi, gebildet wird. Während der Abkühlung findet in diesen Kompositen bei etwa 325 K eine martensitische Umwandlung der B2-Phase zur orthorhombischen B19-TiNi Phase statt. B2- und B19-TiNi weisen eine gute Verformbarkeit von bis zu 30% bei Raumtemperatur unter Zugbelastung auf. Die hier erzeugten Ti-Cu, Ti-Cu-Ni, Ti-Cu-Ni-Zr, Ti-Cu-Ni-Zr-(Si) und Ti-Cu-Ni-Co-Legierungen basieren auf Literaturangaben und Vorhersagen bezüglich der Glasbildungsfähigkeit in diesen Systemen mittels λ+Δh1/2-Kriterium, welches die Auswirkungen der Atomgrößenunterschiede der Elemente und deren elektronische Wechselwirkung einbezieht. Die Proben wurden im Schmelzspinnverfahren (Bänder) und mittels Saugguss in einer Cu-Kokille (Stäbe und Bleche) hergestellt. Die Weiter- und Neuentwicklung von Legierungen, beginnt mit dem Ti-Cu-System. Die Glasbildungsfähigkeit in diesem binären System ist nur gering, so dass lediglich mikrometerdicke amorphe Bänder hergestellt werden können. Die Ergebnisse zeigen, dass der beste Glasbildner eine Zusammensetzung von etwa Ti50Cu50 hat. Die Glasbildungsfähigkeit von binären Legierungen kann durch die Zugabe von Ni weiter verbessert werden. Dies führte innerhalb dieser Arbeit zur Entwicklung neuer Ti-Cu-Ni Formgedächtnis-Glas-Matrix Komposite, in welchen die orthorhombische Martensitphase in der Glas-Matrix ausgeschieden wird. Diese ternären Legierungen zeigen eine hohe Zugfestigkeit in Kombination mit einer hohen Bruchdehnung. Beim Überschreiten einer Temperatur von etwa 320 K vollziehen die Ausscheidungen eine reversible martensitische Umwandlung vom B19- zum B2-Strukturtyp. Durch die amorphe Matrix wird die Hochtemperaturphase (B2 Phase) stabilisiert. Dies verursacht unterschiedliche Umwandlungstemperaturen im Kompositmaterial, die davon abhängig sind, ob die Ausscheidungen nur teilweise oder vollständig in der Matrix eingebettet sind. Die Verformung beginnt in der weichen kristallinen Phase, welche eine heterogene Spannungsverteilung in der Glas-Matrix erzeugt und eine hohe Dichte an Scherbändern in der Matrix verursacht. Die Ausscheidungen haben zudem die Funktion, die Ausbreitung der Scherbänder zu blockieren und das Versagen des Materials zu verzögern. Die Größe der Komposite ist jedoch auf Grund der geringen Glasbildungsfähigkeit auf einen Stabdurchmesser von ca. 1 mm begrenzt. Dies kann mit dem Zulegieren von CuZr verbessert werden. Es wurden hier auf diese Weise neue Ti-Cu-Ni-Zr Komposite entwickelt, deren Durchmesser zwischen 2 und 3 mm liegt. Diese bestehen hauptsächlich aus sphärischen Ausscheidungen der kubischen B2-(Ti,Zr)(Cu,Ni)- und der Glasphase. Die wechselseitige Beziehung zwischen der Streckgrenze und dem Volumenanteil der B2-Phase wurde im Detail untersucht. Für kristalline Volumenanteile kleiner als 30 Vol.-% folgt die Streckgrenze der Mischungsregel und für größere Volumenanteile dem „lasttragenden Modell“ (load bearing model). Die Bruchdehnung wird ebenfalls vom Volumenanteil der Phasen beeinflusst und zeigt ein Maximum bei etwa 30 Vol.-% an B2-Phase. Dies stimmt mit der Vorhersage des „Drei-Element-Modells“ überein. Es wurde festgestellt dass die kubische B2-Phase während der Verformung eine martensitische Umwandlung durchführt, was die starke Kaltverfestigung und die hohen Bruchspannungen dieser Legierungen zur Folge hat. Die Glasbildungsfähigkeit von TiCu-Basislegierungen kann im Gegenzug weiterhin durch geringe Si-Zusätze gesteigert werden. Hierbei tritt jeweils ein Maximum bei Zusätzen von 1 und 0,5 at-% Si zu binären Ti-Cu- oder zu quarternären Ti-Cu-Ni-Zr-Legierung auf. Das Optimum der Glasbildungsfähigkeit ist das Ergebnis sowohl eines geringeren Anteils hochschmelzender Ti5Si3-Ausscheidungen, die als Keimbildner für andere kristalline Phasen dienen, als auch der erhöhten Stabilität der Schmelze sowie der unterkühlten Schmelze. Der Zusatz von Co wiederum hat einen gegenteiligen Effekt. Er vermindert die Glasbildungsfähigkeit von Ti-Cu-Ni-Legierungen drastisch. Zudem scheinen sowohl die martensitische Umwandlungstemperatur als auch das mechanische Verhalten mit der Zahl und Konzentration der Valenzelektronen der B2-Phase zu korrelieren. Die Umwandlungstemperatur sinkt mit steigender Valenzelektronenkonzentration. Eine ausgezeichnete Kombination von hoher Streckgrenze und Bruchdehnung tritt für die Legierungen Ti-Cu-Ni-Zr und Ti-Cu-Ni-Zr-Si mit einem relativ geringen CuZr-Anteil auf. Die Bruchdehnung unter Druck ist fast zweimal höher als es für CuZr-Basis-Komposite gewöhnlich beobachtet worden ist. Die Legierung Ti45Cu39Ni11Zr5 zeigt beispielsweise eine Streckgrenze von 1490±50 MPa in Kombination mit einer plastischen Dehnung von 23,7±0,5%. Für die CuZr-reicheren Ti-Cu-Ni-Zr Zusammensetzungen wurde jedoch eine geringere Duktilität festgestellt, was das Resultat spröder Cu2TiZr-Ausscheidungen in der Glas-Matrix ist. Die vorliegende Arbeit erweitert folglich das Konzept der „Formgedächtnis-Glas-Matrix Komposite“, welches bisher auf CuZr-basierte Legierungen beschränkt war und liefert wichtige Einblicke in die Beziehung zwischen Phasenbildung und mechanischen Eigenschaften der neuen Klasse hochfester TiCu-Basislegierungen, welche nach weiterer Optimierung vielversprechend sein könnten für Hochleistungsanwendungen wie Durchflussmesser, Sensoren und mikrometer- und mm-große Antriebe.

碩士
義守大學
材料科學與工程學系碩士班
98
Jang et al. has reported that micrometer-sized and nano-sized precipitates homogeneous dispersed in the glassy matrix, those precipitates act as discrete obstacles in the amorphous matrix, avoiding catastrophic shearing-off through the whole sample and so as to significantly improve their plasticity. There are combine two kinds of ex-situ dispersed particles, micro-sized (5-30um), and in-situ dispersed precipitates, nano-sized (20-100nm), were found homogeneously distributed in the Zr-Cu-Ni-Al-Ta amorphous matrix. The thermal and the mechanical properties of these Zr-based BMGCs were systematically investigated by the combination of DSC, XRD, SEM, TEM, and compression test. The result of compression test exhibits the yield strength of these BMGCs around 1750-1850 MPa. The compression plastic strain presents a dramatically increasing trend with the Ta content and a plastic strain more than 24% can be obtained for the Zr53Cu26Ni9Al8Ta4 BMGC rod with 2mm in diameter. The fracture surface of the Zr53Cu26Ni9Al8Ta4 BMGC compressive specimen reveals the mixed morphologies, consisting of vein-like pattern and highly rough regions, however these two morphologies more random with increasing the Ta content. Final nano-sized precipitates and micro-sized particles act as discrete obstacles homogeneous dispersed in the glassy matrix. Thus separate and restrict the highly energy shear-banding, avoiding catastrophic shearing-off through the whole sample and so as to significantly improve their plasticity.

碩士
義守大學
材料科學與工程學系碩士班
97
Among the numbers of developed bulk metallic glasses (BMGs) recently, Zr-based BMG was considered to be one of the most promising materials and has attracted much attention due to its exceptional properties, such as a high strength, high hardness, high elastic strain up to 2%, good wear resistances. However, the resulting monolithic bulk metallic glasses (BMGs) usually demonstrate highly inhomogeneous deformation below the glass-transition temperature even under compressive loading with or without confinement.Thus, there are two main approaches to solve the problem of low plastic strain, one is to in-situ precipitate crystalline phases in the BMG matrix, the other is to ex-situ introduce foreign particles or micrometer-sized pores into the BMG matrix. The advantage of in-situ composites over the ex-situ one in the sample preparation is that they can obtain a finer crystalline precipitates by simply adjusting the alloy composition or cooling rate, thus has attracted more attention recently. The Zr53Cu30-xNi9Al8Tax (x =0,2, 4, 6, 8) bulk metallic glass composites (BMGCs) rods with a diameter of 2 ~ 3 mm have been successfully fabricated by suction casting method in this study. The thermal and the mechanical properties of these Zr-based BMGCs were systematically investigated by the combination of DSC, XRD, SEM, TEM, and compression test. Thermal properties analysis, the GFA index(γ and γm, γ=0.428 and γm=0.768) of the Zr53Cu22Ni9Al8Ta8 BMCGs exhibits optimum value.The activation energy of these Zr53Cu30-xNi9Al8Tax alloys decreases with Ta content at beginning and then increases back to 250 kJ/mole at the Zr53Cu22Ni9Al8Ta8 BMGC, which closes to the value of the base BMG (260 kJ/mole). This implies that the Zr53Cu22Ni9Al8Ta8 may have the better thermal stability than the others in the Zr53Cu30-xNi9Al8Tax amorphous alloy system. Microstructure analysis, The XRD patterns of the BMGC rods with 3 mm in diameter demonstrate the amorphous matrix phase with a broadened and diffused humps in the 2θ range of 30°- 50° for all of these Zr53Cu30-xNi9Al8Tax (x =0,2, 4, 6, 8) alloys. No apparent crystalline peak is detected except the high intensity crystalline peaks from the BCC-structured Ta-rich particles when the addition of Ta increases ton 4 at%. The metallographic examination by SEM also revealed that only small amount of Ta-rich particles with size of submicron meter occurs at the Zr53Cu28Ni9Al8Ta2 amorphous alloy. When increases the Ta content more than 2 at%, the volume fraction of these Ta-rich particles increases with Ta addition clearly. In parallel, many Ta-rich particles with size around 10-30 ?m can be observed in the amorphous matrix. the TEM observation also revealed that lots of nano-sized precipitates in the range of 20-80nm embedded in the amorphous matrix for the as-cast Zr53Cu22Ni9Al8Ta8 BMGC rod with diameter of 3mm, these nano-size precipitates were also confirmed to be a BCC structure Ta-rich phase with lattice constant about 0.3332 nm by the nano beam diffraction. Mechanical properties analysis, The result of hardness test for these Zr53Cu30-xNi9Al8Tax amorphous alloys reveals that the macro hardness of these BMGCs does not change much by the addition of Ta, they all have hardness around 570-590 in Hv. In addition, the result of compression test exhibits a similar trend of yield strength as the hardness test, the yield strength of theses BMGCs all keeps at the similar level, around 1720-1760 MPa. On the other hand, the compression plastic strain presents a dramatically increasing trend with the Ta content and a plastic strain more than 30% can be obtained for the Zr53Cu22Ni9Al8Ta8 BMGC rod with 2mm in diameter. The fracture surface of the Zr53Cu22Ni9Al8Ta8 BMGC compressive specimen reveals the mixed morphologies, consisting of vein-like pattern and highly rough regions.Finally,the homogeneous dispersed Ta-rich particles were believed to act as a network in the glassy matrix, thus separate and restrict the highly localized shear-banding to isolated regions, avoiding catastrophic shearing-off through the whole sample and so as to significantly improve their plasticity.

碩士
國立中央大學
機械工程學系
107
Mg-Zn-Ca bulk metallic glass(BMG) is a well-known candidate for bio-implant application due to its biocompatibility and uniform biodegradability which is suitable for suture anchor. Suture anchors are utilized as fixation devices in orthopedic surgery for repair of soft tissue injuries in the knee, shoulder, hip and ankle joints. However, the intrinsic brittleness of Mg-Zn-Ca BMG has to be significantly improved for commercial application. Accordingly, the concept of ex-situ adding ductile metallic particles was introduced to produce the Mg-Zn-Ca bulk metallic glass composite (BMGC) to meet the requirement of mechanical property for the application of suture anchor. In this Study, the Mg66Zn29Ca5 BMG was selected as the base alloy and added with different micro-sized spherical metal particles (Fe or porous Mo or TiZr-based metallic glass particles) to enhance its fracture toughness. The optima results occur at 3 mm Mg-Zn-Ca BMGC rods with 15 vol.% porous Mo particles, the fracture toughness increased upto 6.01 MPa‧m1/2 and remained the maximum compressive strength of 702 MPa. Due to the limitation of cooling rate, both Mg66Zn29Ca5 BMG and BMGC rods with 4 mm in diameter present only partial amorphous status. Therefore, a novel core-shell structure rod was developed, with pure Mg rod as core and Mg66Zn29Ca5 BMG and BMGC as shell to increase the cooling rate. As a result, the 1.25 mm thick shell area of 4 mm core-shell BMGCs rods (added with porous Mo particles) exhibits a fully amorphous matrix co-existing with Mo particles. The optimum performance occurs at the 4 mm core-shell rods with 15 vol.% porous Mo particle additions, the fracture toughness increased from 1.5 to 4.81 MPa∙m1/2 and remained the maximum compressive strength of 589 MPa.

碩士
國立成功大學
材料科學及工程學系
107
Mg-Cu-Gd metallic glass powders were synthesized by Rapid-Solidifying Atomization (RSA). The RSAed powder was fully amorphous shown by X-Ray Diffractometry (XRD), and the glass transition temperature (Tg), crystallization temperature (Tx) and incubation time were determined by Differential Scanning Calorimeter (DSC). The value of Trg and γ were criterion with the glass forming ability (GFA) of Mg-based metallic glass. The Mg-Cu-Gd/Cu ex-situ metallic glass powders is synthesized by electroless plating via different coating time. The bulk Mg-Cu-Gd/Cu ex-situ metallic glass composite is consolidated by hot pressing and backward extrusion. The micro structure is studied by Scanning Electron Microscope(SEM).

博士
國立中山大學
材料與光電科學學系研究所
101
CuZrAl and CuZrAl-V and CuZrAl-Co amorphous alloys were cast by rapid suction casting. Flow serrations and fracture morphologies of the base monolithic Cu50Zr43Al7 bulk metallic glasses (BMGs) are first studied by compression at a low strain rate and analyzed by an energy release perspective. Vanadium or cobalt from 3 to 10 at% is alloyed to the amorphous CuZrAl base alloys to induce precipitation in order to form the bulk metallic glass composites (BMGCs) with micro-sized second phase domains. The V-rich second phase formed during rapid cooling possesses a sharp dendrite shape, inducing stress concentration in the amorphous matrix and lowering the mechanical performance. The Co-rich phase, formed from liquid phase separation, possesses round morphology, lowering the stress concentration and raising or sustaining the mechanical properties. Meanwhile, 1 at% vanadium was alloyed to the amorphous CuZrAl base alloy to induce nano-sized B2-CuZr phase formation in order to improve compressive plasticity. It was found that the dilute vanadium addition induced B2-CuZr formation and, thus, improved plasticity of the CuZrAl alloy. The role of vanadium on plasticity improvement was discussed in the frame of shear band multiplication, energy dissipation during shear banding, twinning/phase transformation of the B2-CuZr particles during deformation, and deformation induced B2-CuZr particle coarsening. It was suggested that such transformation induced plasticity would show dependence on the B2 particle size, which in-turn depends on the inlet shape of the suction casting mold in use. It follows that the final task of this research was to examine the effects of the B2 size and distribution, resulted from the sharp or blunt inlet mold, on the mechanical plasticity in the CuZrAl and CuZrAlCo BMGs and BMGCs. It appears that the B2 particles need to be over some critical size to induce the martensitic/twinning transformation into the B19’ phase (sometimes with twins embedded). An analytic model, based on melt flow dynamics with or without vena contraction, is established, and the agreement between experiment and model is satisfactory.

碩士
義守大學
材料科學與工程學系碩士班
98
(Cu36Zr48Al8Ag8)100-xSix (x = 0–1) amorphous alloy rod with (2~4)mm diameter were prepared by arc melting. The thermal properties and microstructure development during the annealing of amorphous alloys have been investigated by the combination of differential scanning calorimetry (DSC), scanning electron microscope (SEM) with energy dispersive spectrometer (EDS) capability, X-ray diffractometry (XRD),Vickers microhardness test and (TEM) techniques. The XRD result reveals that all these as-quenched, (Cu36Zr48Al8Ag8)100-xSix alloy exhibit broad diffraction patterns of amorphous phase. A clear Tg (glass transition temperature) and supercooled region (about 99 K) were revealed for all of those amorphous alloy rods. The crystallization temperature (Tx) and supercooled region (ΔTx) present a increasing trend with increasing Si content. TEM shows a homogenous and non-contrast pattern for the (Cu36Zr48Al8Ag8)100-xSix rods sample. The microhardness of CuZr base also increases with increasing Si content. The CuZr alloys exhibit highcompressive fracture strength of 1504–2070MPa with plastic strain of 0.1–3.0%。

碩士
義守大學
材料科學與工程學系碩士班
97
In recent years, The Zr-Cu-Al-Ag alloy system is expected to have higher GFA and higher stabilization of supercooled liquid. Jang et al. has reported that adding silicon could effectively increase the activation energy of crystallization as well as increasing the incubation time for the Zr-base amorphous alloys. Therefore, the high GFA (glass forming ability) Cu42Zr42Al8Ag8 amorphous alloy is selected as the base alloy to investigate the effect of microalloying with Si. The (Cu42Zr42Al8Ag8)100-xSix amorphous alloy rods, x =0 to 1, with 2~4 mm in diameter were prepared by Cu-mold drop casting method. The glass forming ability, thermal properties and microstructure evolution was studied by differential scanning calorimetry (DSC), and X-ray diffractometry (XRD). The XRD result reveals that these as-quenched (Cu42Zr42Al8Ag8)100-xSix alloy rods exhibit a broaden diffraction pattern of amorphous phase. The crystallization temperature and GFA (glass forming ability) of (Cu42Zr42Al8Ag8)100-xSix alloys increase with the silicon additions. In addition, both of the activation energy of crystallization and the incubation time of isothermal annealing for these (Cu42Zr42Al8Ag8)100-xSix alloys indicates that the (Cu42Zr42Al8Ag8)99.25Si0.75 alloy posses the best thermal stability among the (Cu42Zr42Al8Ag8)100-xSix alloy system. The Cu42Zr42Al8Ag8 alloy promoted the hardness with increasing Si content. the compression fracture strength and plastic strain can be reached about 2000 MPa and 3 % for the 1 at%Si and 0.5 at% amorphous alloy. Fracture occurs along the maximum shear stress plane, which is inclined at 45° to the direction of compressive loading，it have max stress for shear stress. Many shear bands can be observed on the side surfaces near the fracture area for the good plasticity.

碩士
義守大學
材料科學與工程學系碩士班
98
We have successfully synthesized the Ti particles reinforced Mg58Cu28.5Gd11Ag2.5 metallic glass composites (BMGCs) rods with a diameter of 2 ~ 4 mm by injection casting method in an Ar atmosphere. The glass forming ability (GFA) and the mechanical properties of these Mg-based BMGCs have been systematically investigated as a function of Vf of Ti particles. The results show that the compressive ductility increases with the volume fraction of Ti particles. A drastically improvement of compressive plastic strain and reaches up to 24% occurs at the Mg-base BMGC with 40 vol% Ti particles. In parallel, multiple-shear bands were revealed on the sample surface after compression test. This suggests that these dispersed Ti particles can highly absorb the energy of shear banding and branch the primary shear band into multiple shear bands, thus decrease the stress concentration for further propagation of shear band and so as to significantly enhance plasticity. Additionally, the yield strength can be kept at 800 MPa as increasing the addition of Ti particles to 40 vol.%. This was found presumably due to the good bonding of interface between the Ti particle and amorphous matrix.

碩士
義守大學
材料科學與工程學系碩士班
96
We present a porous ductile Mo particles reinforced Mg-based metallic glass composite, exhibiting superior mechanical performance with up to 10% compressive strain and 1100 MPa stress at room temperature. For a given amount of particles, the porous particles will generate more interfaces between the reinforcements and matrix and, thus, can confine lots of microsized compartments of the Mg based glassy phase within the porous particles. This promotes the deformation to distribute more uniformly across the specimens, improving the ductility. The toughness of Mg58Cu28.5Gd11Ag2.5 metallic glass which measured by the indentation method increases with porous Mo content. The KIC value of the metallic glass composite can reach to 25 MPa√m when the Mo content increases to 25 vol.%. We suggest that porous ductile particles might preferably be used to toughen amorphous materials with stubborn brittleness.

碩士
國立中山大學
材料科學研究所
94
The thermal and mechanical properties of the Mg-based bulk metallic glasses are reported in this thesis. The original ingots were prepared by arc melting and induction melting. The thermal and mechanical properties of the Mg-based bulk metallic glasses are reported in this thesis. The original ingots were prepared by arc melting and induction melting. The Mg65Cu25Gd10 and Mg65Cu15Ag10Gd10 bulk metallic glasses with different diameters from 3 to 6 mm were successfully fabricated by conventional copper mold casting in an inert atmosphere. The Mg65Cu25Gd10 bulk metallic glass shows the high glass forming ability and good thermal stability. However, the addition of Ag in the Mg65Cu15Ag10Gd10 alloy degrades the thermal stability. Based on the DSC results, the supercooled liquid region

碩士
國立中央大學
機械工程學系
104
Development of metallic materials is recently essential for biomedical application. Therefore, Zr-based bulk metallic glasses become favorable due to their attractive properties. Zr-Al-Co BMGs, as low-toxic material, having less possibility to harm the human body compared with other Cu-, Ni-, and Be-containing Zr-based BMGs, however, most of them show the limited ductility. The structural modification through partial crystallization on Zr54Al17Co29 BMG was obtained by isothermal annealing and the correlation with the mechanical and corrosion resistance have been investigated. Zr54Al17Co29 BMG rod with diameter of 2, 3, and 4 mm was successfully fabricated by arc melting and suction casting, afterwards, the amorphous properties were examined by XRD, SEM, and DSC. A single broad peak of XRD pattern, good chemical homogeneity, and the information of Tg, Tx, and ∆Tx (742, 794, and 52 K) were obtained from the analyses, indicating the sample was fully amorphous. By Kissinger plots, activation energies of crystallization for the first and second exothermic peak are determined to be 233 and 253 kJ mol-1. The isothermal annealing was conducted at the temperature within SCL region for different times that was determined by JMA isothermal analysis in order to variate sample crystallinities. TEM analysis reveals that ZrCo2Al crystal phase with size of 10 nm is observed from sample with 40.1% crystallinity. Mechanical properties of as-cast and partially crystallized samples containing 6.6; 14.5; 19.8; 25.5; 31.5; 36.4; and 40.1% crystallinities were studied by hardness and compression test. The results reveal that the hardness slightly increases with increasing the crystallinity, in range 540 ± 5 to 575 ± 5 Hv. However, the results of compression test show a different trend, yield strength and plastic strain are significantly improved when the sample reaches 6.6% crystallinity. Afterwards, the deteriorating effect of excess nanocrystal contents for the sample with higher crystallinity on the plastic strain was observed while yield strength remains constant. The sample containing 6.6% crystallinity shows the remarkable improvement of yield strength and plastic strain (2160 ± 110 MPa and 4.7 ± 0.2%), higher than the as-cast counterparts (2130 ± 75 MPa and 2.2 ± 1.6%). This improvement is attributed to the optimum nanocrystal content to restrict the shear bands propagation accompanied without any free volume reduction effect due to short annealing time. In addition, the fracture surface morphology of the sample with 6.6% crystallinity shows the mixed vein and river-like pattern, indicating strong interaction between shear bands and nanocrystals. Moreover, the as-cast and partially crystallized with 6.6% crystallinity samples show similar corrosion resistance and comparable with the 316 stainless steel by potentiodynamic polarization test. In summary, the Zr54Al17Co29 BMG with 6.6% crystallinity is believed as promising candidate for biomaterial applications.

碩士
國立臺灣大學
材料科學與工程學研究所
105
The Zr-Ti-Cu-Nd metallic glass ribbons with different amounts of Nd were fabricated by melt spinning. The ribbons were used to examine the microstructure and the mechanical properties. Since the positive mixing enthalpy between some elements, the phenomenon of liquid phase separation occurred and formed the metallic glass composites. Specifically, Nd separated from the Zr/Ti based metallic glass matrix and precipitated with Cu during the cooling process. In addition to Nd, the distribution of Cu was nonuniform because its mixing enthalpies with Nd and Zr/Ti were different. This was verified by energy-dispersive X-ray spectroscopy. The images from scanning electron microscopy showed that the microstructure was inhomogeneous across the thickness of the ribbon because of the different cooling rates. By examining the hardness, the ribbons were softer in the middle and harder on both surface sides because of the different distributions of precipitates. Using modulus mapping, the matrix showed the higher storage modulus and the precipitates showed the higher loss modulus in contract. The micropillar compression tests showed that the samples with more additive Nd contents presented larger plasticity which proved that the soft second phase in these composites was effective in plasticity enhancements.

碩士
國立中央大學
材料科學與工程研究所
100
Due to the widely used of steel, Fe-based amorphous alloy, also known as amorphous steel, is being studied by many researchers. Comparing to Zr- and Pt-based amorphous alloys, the cost of Fe-based amorphous alloy is the most attracting characteristic, especially. Unfortunately, the lack of plasticity of such material limits its application severely. According to such situation, the ex-situ method is applied in this study where the Fe-based bulk metallic glass composites Fe77Mo5P9C7.5B1.5 was casted with different amount of ex-situ Ta particles addition as the reinforcing phase by tilt mold casting in argon atmosphere. These composite alloys were examined by applying compression loading and indentation so the corresponding mechanical properties were then acquired. The BMG composite with 13vol. % Ta particles possessing a fracture toughness of 139.4 MPa m0.5 can sustain a plastic strain to failure of 6.43% at compressive fracture strength as high as 3.18GPa where the angle between the compressive shear plane and loading axis is ~38.8° while zero plasticity without reinforcing phase particles being distributed. Depending on SEM observation and analysis, the heterogeneous phase particles dispersing in the matrix decreased own sizes after casting which hold better performance to stop the propagation of micro-cracks. However, the formation of tantalum carbide which processing larger hardness and elastic modulus reduced the fraction of ductile Ta phase and thus harmed the plasticity eventually. The results of this study tended to solve the problems of fast propagation of shear bands and micro-cracks in Fe-based BMGs further providing an effective solution to improve the plasticity.

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
義守大學
材料科學與工程學系碩士班
98
To generate a rapid welding thermal cycle and eliminate the crystallization for a (Zr53Cu30Ni9Al8)Si0.5 bulk metallic glass (BMG) weld, the Nd:YAG single pulse laser welding process was used in this study.The test samples were welded with different parameters combinations, under the room temperature or lower initial temperatures. As the test accomplished, microstructure evolution in heat affected zone (HAZ) or weld fusion zone (WFZ) was studied by using OM, TEM, SEM, EDS or XRD.The results show that at room temperature with the single-pulsed laser welding approach, crystallization in the HAZ seems unavoidable while the WFZ appears crystal-free. As the initial temperature was decreased to 0oC, both WFZ and HAZ show the amorphous state. The crystallization phase was identified as Zr2Cu with crystal size from 50nm to 100nm.Furthermore, it was observed when the precipitates were greater in the HAZ, cracks were more likely to form, and hardness in the HAZ was decreased.Finally, using the optimal single pulse welding parameters, this study develops an innovated laser welding process to complete a continuous weld. Initially, this process finishes the odd numbers of single pulse weld. After that, every odd number weld was joined by the even numbers of single pulse weld. This approach can eliminate the pre-heat or post-heat effects on the weld which suppress the formation of the crystallization in the welds.Based on the above results, the effects of Nd:YAG laser welding parameters on the microstructure evolution and mechanical property for (Zr53Cu30Ni9Al8)Si0.5 BMG was established. Moreover, this results would be helpful to (Zr53Cu30Ni9Al8)Si0.5 BMG for the further applications.

碩士
國立中央大學
材料科學與工程研究所
105
In some Zr-based bulk metallic glass composites (BMGCs), the ZrCu B2 phase can be precipitated from the matrix. When the ZrCu B2 phase subjected to the stress from the shear banding, it will absorb the energy of shear band and transform into ZrCu B19' phase, and so as to improve the plasticity of Zr-based BMG. However, the particle size and distribution of ZrCu B2 phase in Zr48Cu47.5Al4Co0.5 BMG cannot be well controlled in general casting. Large agglomerated and inhomogeneous distributed ZrCu B2 phase were usually found in the Zr48Cu47.5Al4Co0.5 BMG samples. Therefore, the concept of inoculation in conventional solidification process is applied in this study. The Ta particles (size of 5–30 µm) with 0 ~ 1.0 vol.% were added into Zr48Cu47.5Al4Co0.5 BMG matrix as the inoculant. By using the ultrahigh melting point of tantalum and immiscible with Zr-base substrate, the Ta particles can be uniformly dispersed in the Zr-based alloy melt as the nucleation sites for precipitating ZrCu B2 phase, and form a homogeneously distributed ZrCu B2 phase in the matrix of Zr48Cu47.5Al4Co0.5 BMG. Then, the different cooling rates of solidification process are further used to control the particle size of ZrCu B2 phase. Based on the results of XRD analysis, Zr48Cu47.5Al4Co0.5 alloy rods with 0 ~ 0.75 vol.% Ta particle additions made by the copper mold at the temperature of -30°C present amorphous structure co-existing with ZrCu B2 phase. However, when the temperature of copper mold increases to higher than -20 °C, the sample with 0.75 vol.% Ta particle additions will be totally crystallized. After adding Ta particles, the precipitates of ZrCu B2 phase in the Zr48Cu47.5Al4Co0.5 alloy matrix exhibit more even distribution and round shape. But when decrease the cooling rate of solidification, the large amount of ZrCu B2 precipitates will agglomerate and form a large particle. According to the results of DSC analysis, with increasing the amount of Ta particles and decreasing the cooling rate of solidification, the enthalpy value of crystallization exothermic peak decreases, which means that the volume fraction of amorphous matrix decreased and the precipitate of ZrCu B2 phase increased. The results of compression test reveal that the sample of Zr48Cu47.5Al4Co0.5 added with 0.75 vol.% Ta particle performs the highest mechanical properties, 1750 MPa yield stress, 1890 MPa fracture stress, and 14 % plastic strain. This is 6.5 % improvement of plastic strain in comparison with its base alloy.

Amorphous alloys possess attractive combinations of mechanical properties (high elastic limit, ~2%, high fracture toughness, 20-50 MPa.m1/2, etc.) and exhibit mechanical behavior that is different, in many ways, from that of the crystalline metals and alloys. However, fundamental understanding of the deformation and fracture mechanisms in amorphous alloys, which would allow for design of better metallic glasses, has not been established on a firm footing yet. The objective of this work is to understand the deformation and fracture mechanisms of amorphous materials at various length scales and make connections with the macroscopic properties of glasses. Various experimental techniques were employed to study the macroscopic behavior and atomistic simulations were conducted to understand the mechanisms at the nano level. Towards achieving these objectives, we first study the toughness of a Zr-based bulk metallic glass (BMG), Vitreloy-1, as a function of the free volume, which was varied by recourse to structural relaxation of the BMG through sub-Tg annealing treatment. Both isothermal annealing at 500 K (0.8Tg) for up to 24 h and isochronal annealing for 24 h in the temperature range of 130 K (0.65Tg) to 530 K (0.85Tg) were conducted and the impact toughness, Γ, values were measured. Results show severe embrittlement, with losses of up to 90% in Γ, with annealing. The variation in Γ with annealing time, ta, was found to be similar to that observed in the enthalpy change at the glass transition, ΔH, with ta, indicating that the reduction of free volume due to annealing is the primary mechanism responsible for the loss in Γ with annealing. Having established the connection between sub-atomic length scales (free volume) and macroscopic response (toughness), we investigated further the affects of relaxation on intermediate length scale behavior, namely deformation induced by shear bands, by employing instrumented indentation techniques. While the Vickers nano-indentation response of the as-cast and annealed glasses do not show any significant difference, spherical indentation response shows reduced shear band activity in the annealed BMG. Further, relatively high indentation strain was observed to be necessary for shear band initiation in the annealed glass, implying an increased resistance for the nucleation of shear bands when the BMG is annealed. In the absence of microstructural features that allow for establishment of correlation between properties and the structure, we resort to atomistic modeling to gain further understanding of the deformation mechanisms in amorphous alloys. In particular, we focus on the micromechanisms of strain accommodation including crystallization and void formation during inelastic deformation of glasses. Molecular dynamics simulations on a single component system with Lennard-Jones-like atoms suggest that a softer short range interaction between atoms favors crystallization. Compressive hydrostatic strain in the presence of a shear strain promotes crystallization whereas a tensile hydrostatic strain was found to induce voids. The deformation subsequent to the onset of crystallization includes partial re-amorphization and recrystallization, suggesting important mechanisms of plastic deformation in glasses. Next, a study of deformation induced crystallization is conducted on two component amorphous alloys through atomistic simulations. The resistance of a binary glass to deformation-induced-crystallization (deformation stability) is found to increase with increasing atomic size ratio. A new parameter called “atomic stiffness” (defined by the curvature of the inter-atomic potential at the equilibrium separation distance) is introduced and examined for its role on deformation stability. The deformation stability of binary glasses is found to increase with increasing atomic stiffness. For a given composition, the internal energies of binary crystals and glasses are compared and it is found that the energy of glass remains approximately constant for a wide range of atomic size ratios unlike crystals in which the energy increases with increasing atomic size ratio. This study uncovers the similarities between deformation and thermal stabilities of glasses and suggests new parameters for predicting highly stable glass compositions.