Macroscopic ductility is promoted in bulk metallic glasses by both composite reinforcements (at low temperatures) and by the activation of viscous flow mechanisms (at high temperatures). It is of fundamental interest to understand deformation physics when both of these strategies are employed at the same time. Despite the quickly growing literature around the room-temperature mechanical properties of metallic glass matrix composites (MGMCs), the deformation behavior of MGMCs over a wide range of temperatures and strain rates has yet to be systematically investigated, especially at high temperatures close to Tg. Here the high temperature compressive behavior of Zr-based MGMCs with in-situ reinforcements is explored systematically over a series of strain rates. Additionally, the volume fraction of second-phase reinforcements was tailored to explore its effect on both inhomogeneous and homogeneous deformation modes. / Singapore-MIT Alliance (SMA)

In order for composites to become an accepted material for infrastructure application, life prediction and durability must be understood. The majority of studies have examined the strength and fatigue response of composites under hot and/or moist conditions. Various researchers have also studied life prediction methods for composite materials under fatigue, primarily for high performance applications. Little work has been done to study durability under combined service conditions for composites used in civil infrastructure applications. This thesis focuses on the development of a life prediction model for use with fiber reinforced polymer composites in bridge service environments. The Tom's Creek Bridge of Blacksburg, VA is used as a guiding case study. First, the tensile properties of the composite were studied as a function of temperature and moisture. Damage accumulation was studied as a function of cyclic loading and temperature cycles. The enviro-mechanical conditions, including moisture, temperature and fatigue loading, were then used in a computer simulation to predict the life of a vinyl ester/glass composite under an approximate bridge service environment. Finally, a laboratory simulation was conducted that approximates the temperature and humidity that is seen at the Tom's Creek Bridge, but in an accelerated time frame. A multi-stress fatigue pattern, mimicking cars and trucks passing over the bridge, was used. One year of conditions was accelerated to approximately six hours and thirty-three minutes using a servo-hydraulic test frame and environmental chamber. The final results showed that life prediction methodology conservatively predicted the lifetime of a vinyl ester/glass composite under the enviro-mechanical conditions. The damage of the composite was predominately driven by cyclic loading. The environmental conditions of moisture and temperature had only a small affect on the lifetime of the composite. This lack of environmental sensitivity is largely due to the durability of the resin system. / Master of Science

Metallic glasses (MGs) are very attractive for structural applications due to their large elastic strain, high strength and hardness, resulting from their unique atomic structure. However, MGs are brittle. Preparing metallic glass–crystal composites (MGCCs) from parent glass through thermal treatment is a useful method to induce ductility and work hardening. Thus, besides the direct applications of as-prepared MGs, the glasses can be used as a starting material to be processed, for example, by thermoplastic forming or thermal treatment to design components with desired shape and/or properties. In this view, it is of high importance to know the phase- transformation mechanisms and kinetics upon heating MGs, especially for rapid heating, which has not been sufficiently studied yet. CuZrAl-based alloys, with near CuZr equimolar compositions, are suitable for producing MGCCs with improved plasticity owing to their good glass-forming ability and the formation of ductile B2 CuZr phase upon crystallization. However, the crystallization mechanism(s) and products have mainly been elucidated by extrapolating the available knowledge of the binary CuZr system. In the present work, a set of complementary techniques including resistive (Joule) heating, in situ high-energy synchrotron X-ray diffraction, conventional and ultrafast differential scanning calorimetry and containerless solidification during electromagnetic levitation is used to map the phase evolution ― crystallization and solid-state phase transformations ― in Cu₄₇.₅Zr₄₇.₅Al₅, Cu₄₇.₅Zr₄₈Al₄Co₀.₅ and Cu₄₆.₅Zr₄₈Al₄Nb₁.₅ MGs during isokinetic and isothermal annealing. The resistive heating devices, custom-built at the Leibniz Institute for Solid State and Materials Research Dresden – IFW Dresden, enable heating rates Φ to range from 10¹ up to 10⁵ K s⁻¹ in a vacuum. Using the obtained experimental data, continuous-heating-transformation (CHT) diagrams for a heating rate range exceeding six orders of magnitude, covering the entire supercooled liquid region, and time-temperature-transformation (TTT) diagrams are constructed. The transformation maps reveal the competition between the Cu₁₀Zr₇, B2 CuZr and τ4 (Cu₂ZrAl) phases during crystallization. The formation of the primary phase and transformation sequence depends on the MG composition as well as on the heating rate. The critical heating rate to bypass the crystallization increases from ~30 000 K s⁻¹ for Cu₄₇.₅Zr₄₇.₅Al₅ MG to ~40 000 K s⁻¹ for Cu₄₆.₅Zr₄₈Al₄Nb₁.₅ MG and to ~90 000 K s⁻¹ for Cu₄₇.₅Zr₄₈Al₄Co₀.₅ MG, reflecting their glass-forming ability. The optimum heating rate to obtain glass–crystal composites with the predominant and desired B2 CuZr phase is evaluated to be Φ > 1 000 K s⁻¹ for Cu₄₇.₅Zr₄₇.₅Al₅ MG, Φ > 1 500 K s⁻¹ for Cu₄₇.₅Zr₄₈Al₄Co₀.₅ MG, and Φ > 4 000 K s⁻¹ for Cu₄₆.₅Zr₄₈Al₄Nb₁.₅ MG. Cu₄₆.₅Zr₄₈Al₄Nb₁.₅ MG shows an increased propensity for the formation of brittle Cu₁₀Zr₇ intermetallic phase, compared to Cu₄₇.₅Zr₄₇.₅Al₅ and Cu₄₇.₅Zr₄₈Al₄Co₀.₅ MGs. The TTT diagram for the isothermal heating of Cu₄₆.₅Zr₄₈Al₄Nb₁.₅ shows an apparent double-nose shape which corresponds to the primary crystallization of Cu₁₀Zr₇ at lower temperatures and B2 CuZr at higher temperatures.

No description available.

A simulation model which incorporates the statistical- and numerical-based Lattice Green Function Local Load Sharing Model and a Fracture Mechanics-based Residual Strength Model has been developed. The model simulates creep rupture by imposing a fixed load of constant stress on the composite over the simulation duration. Simulation of the fatigue of glass fiber-reinforced composites is achieved by replacing the constant stress parameter in the model with a sinusoidal wave function. Results from the creep rupture model using fused silica fiber parameters, compare well with S-2 glass/epoxy systems. Results using Mandell's postulate that fatigue failure in glass fiber-reinforced polymeric composites is a fiber-dominated mechanism, with a characteristic slope of 10 %UTS/decade are consistent with available experimental data. The slopes of fatigue curves for simulated composites for three frequencies namely: 2, 5 and 10 Hz are within 12-14 %UTS/decade compared with that of 10.6-13.0%UTS/decade for unidirectionl glass reinforced composites (epoxy and vinyl ester) obtained from Demers' [40] data. / Master of Science

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.

No description available.

Woven glass composites have been used for many years in commercial applications due to their light weight, competitive price and good engineering properties. Absorption of energy by laminated composite material results in damage in various forms, the most common of which is delamination. Inter-laminar fracture causes the layers of composite to separate, resulting in a reduction in stiffness and strength of the composite structure, matrix cracking and in some cases fibre breakage takes place. The aim of this project was to improve the inter-laminar bond strength between woven glass fabric and resin. Air jet texturing was selected to provide a small amount of bulk to the glass yarn. The purpose was to provide more surface contact between the fibres and resin and also to increase the adhesion between the neighbouring layers. These were expected to enhance the resistance to delamination in the woven glass composites.Glass yarns were textured by a Stähle air jet texturing machine. Core-and-effect yarn was produced instead of a simple air textured yarn. Hand loom and vacuum bagging techniques were used for making the fabric and composite panels from both textured and non-textured yarns. Density and fibre volume content were established for physical characterisation. Breaking strength (tenacity) of the yarns and tensile, flexure, inter-laminar shear strength (ILSS) and fracture toughness (mode 1) properties of the composites were determined. Projection microscopy and SEM imaging techniques were used to assess the fractured surfaces of the composite specimens. The yarn tenacity and the tensile properties of the composites were significantly reduced after the texturing process, whereas flexure properties were unchanged. However, significant improvement was observed in the ILSS and fracture toughness of the composites after the texturing process. It was also observed that the composites made from the fabrics with textured yarns in only the weft direction are the most advantageous as they maintained the tensile and flexure properties but have significantly higher inter-laminar shear strength.

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.:Contents Abstract V Kurzfassung IX 1 Theoretical background 1 1.1 Development of metallic glasses 1 1.2 Formation of metallic glasses 3 1.2.1 Thermodynamic considerations 5 1.2.2 Kinetic considerations 7 1.2.3 Structural considerations 10 1.3 Mechanical properties of metallic glasses 14 1.4 Deformation mechanisms of metallic glasses 18 1.4.1 Shear transformation zone theory 18 1.4.2 Free volume model 20 1.4.3 Potential energy landscape theory 21 1.4.4 Cooperative Shearing Model 22 1.5 Strategies to improve the ductility of metallic glasses 24 1.5.1 Nano-scaled microstructural inhomogeneities 25 1.5.2 Micro-scaled microstructural inhomogeneities 28 1.5.3 CuZr-based BMG composites 31 2 Experimental techniques 37 2.1 Sample preparation 37 2.1.1 Arc melting/suction casting 37 2.1.2 Centrifugal casting 38 2.1.3 High-frequency melting/injection casting 39 2.1.4 Melt spinning 39 2.1.5 Ball milling and powder consolidation 40 2.2 Structure characterizations 41 2.2.1 X-ray diffraction 41 2.2.2 Optical microscopy and scanning electron microscopy 41 2.2.3 Transmission electron microscopy 42 2.3 Thermal analysis 43 2.3.1 Differential scanning calorimetry 43 2.3.2 Dilatometry 44 2.4 Measurement of the elastic constants 44 2.5 Compression and tensile tests 44 3 Strategy for pinpointing the formation of CuZr-based BMG composites 46 3.1 Theoretical analysis for the formation of CuZr-based BMG composites 46 3.2 Nature of the eutectoid B2 CuZr transformation 49 3.2.1 Shift of endothermic peak(s) related to the eutectoid B2 transformation 49 3.2.2 Thermal stability of the B2 CuZr phase 52 3.3 Formation of the amorphous phase and the B2 CuZr phase 54 3.4 A new parameter for pinpointing the formation of CuZr-based BMG composites 57 3.5 Conclusions 59 4 Synthesis of CuZr-based BMG composites 60 4.1 Formation of Type I alloys 60 4.2 Formation of Type II alloys 62 4.2.1 Formation and microstructures of the Cu50Zr50 BMG composites 62 4.2.2 Formation and microstructures of the Cu-Zr-Ti BMG composites 67 4.2.3 Formation and microstructures of the Cu-Zr-Al and Cu-Zr-Ag BMG composites 70 4.3 Formation of Type III alloys 74 4.4 Conclusions 76 5 Processing routes for CuZr-based BMG composites 78 5.1 Influence of the melting current/time 78 5.2 Adjusting the cooling rate 81 5.3 Re-melting of the pre-alloy 82 5.4 Introduction of boron nitride particles 84 5.5 Effect of TaW inoculation 87 5.6 “Flash annealing” 93 5.7 Conclusions 100 6 Yielding and deformation mechanisms of CuZr-based BMG composites 101 6.1 Formation and microstructures of Cu47.5Zr47.5Al5 BMG composites 101 6.2 Deformation behavior of Cu47.5Zr47.5Al5 BMG composites 105 6.3 Yielding and plastic deformation mechanisms 110 6.3.1 Yielding and plastic deformation during stage I 110 6.3.2 Yielding and plastic deformation during stage II 113 6.3.3 Yielding and plastic deformation during stage III 114 6.3.4 Plastic deformation during stage IV 118 6.3.5 Fracture behavior 120 6.4 Modeling of the “yielding” behavior 121 6.5 Conclusions 124 7 Martensitic transformation behavior in CuZr-based alloys 126 7.1 Electronic structures and martensitic transformation 126 7.1.1 Electronic structures of the B2 CuZr phase 127 7.1.2 Electronic structures of CuZr martensites 129 7.2 Effect of minor additions on the martensitic transformation 130 7.2.1 Formation of Cu-Zr-Ti crystalline samples 130 7.2.2 Effect of Ti element on the martensitic transformation 133 7.2.3 Effect of minor elements on the martensitic transformation temperature 135 7.3 Martensitic transformation in rapidly solidified alloys 139 7.3.1 Martensitic transformation in the as-cast Cu50Zr50 alloys 140 7.3.2 Martensitic transformation in the as-cast Cu-Zr-Al alloys 142 7.4 Conclusions 145 8 Shear banding process of CuZr-based BMG composites 146 8.1 Serrated flow in CuZr-based BMG composites 146 8.2 Statistical analysis of the serrations for brittle and ductile BMGs 148 8.3 Different statistical results of the serration events for CuZr-based BMG composites during deformation 152 8.4 Energy criteria for serrations in CuZr-based BMG and their composites 155 8.5 Conclusions 158 9 Summary and Outlook 160 Publications 162 Acknowledgements 163 References 164 Schriftliche Erklärung 191 / 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.:Contents Abstract V Kurzfassung IX 1 Theoretical background 1 1.1 Development of metallic glasses 1 1.2 Formation of metallic glasses 3 1.2.1 Thermodynamic considerations 5 1.2.2 Kinetic considerations 7 1.2.3 Structural considerations 10 1.3 Mechanical properties of metallic glasses 14 1.4 Deformation mechanisms of metallic glasses 18 1.4.1 Shear transformation zone theory 18 1.4.2 Free volume model 20 1.4.3 Potential energy landscape theory 21 1.4.4 Cooperative Shearing Model 22 1.5 Strategies to improve the ductility of metallic glasses 24 1.5.1 Nano-scaled microstructural inhomogeneities 25 1.5.2 Micro-scaled microstructural inhomogeneities 28 1.5.3 CuZr-based BMG composites 31 2 Experimental techniques 37 2.1 Sample preparation 37 2.1.1 Arc melting/suction casting 37 2.1.2 Centrifugal casting 38 2.1.3 High-frequency melting/injection casting 39 2.1.4 Melt spinning 39 2.1.5 Ball milling and powder consolidation 40 2.2 Structure characterizations 41 2.2.1 X-ray diffraction 41 2.2.2 Optical microscopy and scanning electron microscopy 41 2.2.3 Transmission electron microscopy 42 2.3 Thermal analysis 43 2.3.1 Differential scanning calorimetry 43 2.3.2 Dilatometry 44 2.4 Measurement of the elastic constants 44 2.5 Compression and tensile tests 44 3 Strategy for pinpointing the formation of CuZr-based BMG composites 46 3.1 Theoretical analysis for the formation of CuZr-based BMG composites 46 3.2 Nature of the eutectoid B2 CuZr transformation 49 3.2.1 Shift of endothermic peak(s) related to the eutectoid B2 transformation 49 3.2.2 Thermal stability of the B2 CuZr phase 52 3.3 Formation of the amorphous phase and the B2 CuZr phase 54 3.4 A new parameter for pinpointing the formation of CuZr-based BMG composites 57 3.5 Conclusions 59 4 Synthesis of CuZr-based BMG composites 60 4.1 Formation of Type I alloys 60 4.2 Formation of Type II alloys 62 4.2.1 Formation and microstructures of the Cu50Zr50 BMG composites 62 4.2.2 Formation and microstructures of the Cu-Zr-Ti BMG composites 67 4.2.3 Formation and microstructures of the Cu-Zr-Al and Cu-Zr-Ag BMG composites 70 4.3 Formation of Type III alloys 74 4.4 Conclusions 76 5 Processing routes for CuZr-based BMG composites 78 5.1 Influence of the melting current/time 78 5.2 Adjusting the cooling rate 81 5.3 Re-melting of the pre-alloy 82 5.4 Introduction of boron nitride particles 84 5.5 Effect of TaW inoculation 87 5.6 “Flash annealing” 93 5.7 Conclusions 100 6 Yielding and deformation mechanisms of CuZr-based BMG composites 101 6.1 Formation and microstructures of Cu47.5Zr47.5Al5 BMG composites 101 6.2 Deformation behavior of Cu47.5Zr47.5Al5 BMG composites 105 6.3 Yielding and plastic deformation mechanisms 110 6.3.1 Yielding and plastic deformation during stage I 110 6.3.2 Yielding and plastic deformation during stage II 113 6.3.3 Yielding and plastic deformation during stage III 114 6.3.4 Plastic deformation during stage IV 118 6.3.5 Fracture behavior 120 6.4 Modeling of the “yielding” behavior 121 6.5 Conclusions 124 7 Martensitic transformation behavior in CuZr-based alloys 126 7.1 Electronic structures and martensitic transformation 126 7.1.1 Electronic structures of the B2 CuZr phase 127 7.1.2 Electronic structures of CuZr martensites 129 7.2 Effect of minor additions on the martensitic transformation 130 7.2.1 Formation of Cu-Zr-Ti crystalline samples 130 7.2.2 Effect of Ti element on the martensitic transformation 133 7.2.3 Effect of minor elements on the martensitic transformation temperature 135 7.3 Martensitic transformation in rapidly solidified alloys 139 7.3.1 Martensitic transformation in the as-cast Cu50Zr50 alloys 140 7.3.2 Martensitic transformation in the as-cast Cu-Zr-Al alloys 142 7.4 Conclusions 145 8 Shear banding process of CuZr-based BMG composites 146 8.1 Serrated flow in CuZr-based BMG composites 146 8.2 Statistical analysis of the serrations for brittle and ductile BMGs 148 8.3 Different statistical results of the serration events for CuZr-based BMG composites during deformation 152 8.4 Energy criteria for serrations in CuZr-based BMG and their composites 155 8.5 Conclusions 158 9 Summary and Outlook 160 Publications 162 Acknowledgements 163 References 164 Schriftliche Erklärung 191

Boron nitride (BN) materials have unique properties, which has led to interest in them in the last few years. The deformation of boron nitride materials including hexagonal boron nitride, boron nitride nanosheets (BNNSs) and boron nitride nanotubes have been studied by Raman spectroscopy. Both mechanical and liquid exfoliations were employed to obtain boron nitride nanostructures. Boron nitride glass composites were synthesised and prepared in thin films to be deformed by bending test in-situ Raman spectroscopy. Hexagonal boron nitride in the form of an individual flake and as flakes dispersed in glass matrices has been deformed and Raman measurement shows its response to strain. The shift rates were, -4.2 cm-1/%, -6.5 cm-1/% for exfoliated h-BN flake with thick and thin regions and -7.0 cm-1/%, -2.8 cm-1/% for the h-BN flakes in the h-BN/ glass (I) and glass (II) composites. Boron nitride nanosheets (BNNSs) shows a G band Raman peak at 1367.5 cm-1, and the deformation process of BNNSs/ glass composites gives a shift rate of -7.65 cm-1/% for G band. Boron nitride nanotubes (BNNTs) have a Raman peak with position at 1368 cm-1, and their deformation individually and in composites gives Raman band shift rates of -25.7 cm-1/% and -23.6 cm-1/%. Glass matrices shows compressive stresses on boron nitride fillers and this was found as an upshift in the frequencies of G band peak of boron nitride materials. Grüneisen parameters of boron nitride (BN) were used to calculate the residual strains in glass matrices of BNNSs nanocomposites as well as to estimate the band shift rates which found to be in agreement with the experimental shift rate of bulk BN and BNNTs.