A range of new mixed metal carboxylate ((M(O2CR)n) glasses has been prepared. Typically, Mn+ = alkali metals, alkaline earth metals, Zn2+, Pb2+, Sn2+, Co2+ and Cu2+. R increases from CH3 to C7H15 and higher. The alkyl chain can also be branched or aromatic. The properties of these glasses are affected by both the metal cations and carboxylate anions. Densities range from 1.2 to 2.7 g cm-3 and refractive indices from 1.4 to 1.6. Transparency has been shown to extend from 250 to 1400 nm. The carboxylate mixtures could be maintained in the molten state, at temperatures ranging from 100-200°C for prolonged periods without decomposition. Glass transition temperatures have been determined; these generally extended from 30°C up to 60°C. The melts were excellent solvents for a wide range of organic compounds. These dissolved in the carboxylate melts with no appreciable decomposition. The melts could then be quenched to give monolithic glass matrices. By choosing specifically designed organic compounds, the glasses have potential application for photochromism, electrochromism and non-linear optics. Investigation of the solubility of the glasses in water indicated the dependence on cation combination and chain length of the carboxylate ion. These investigations were made to explore the use of the glasses as host media for the release of agrochemical and other compounds with biological activity. It has been shown that Culex quinquefasciatus gives a positive ovipositional response to pheromone that is released from doped glasses over an extended time period. An investigation of the glass structure and the environment it provides for guest materials was undertaken using selected analyses. The structures of zinc carboxylates were determined by X-ray crystallography to provide information pertinent to the nature of the coordination of zinc in these glasses. Organotin compounds were dissolved in carboxylate glasses and studied by 119Sn NMR and Mossbauer spectroscopy. Anion exchange reactions readily occurred in the melts; there was also evidence of Sn-C bond cleavage with certain species. The potential of using Mossbauer spectroscopy as a probe into the glass "structure" is discussed.

Indiana University-Purdue University Indianapolis (IUPUI) / Impact processes, where a meteor strikes a planetary body’s surface, are ubiquitous in the Solar System. These highly energetic events require study by both computational methods and experimental investigation. An impact process of particular interest to our study is the impact plume, a collection of vaporized rock and superheated gases that is produced during an impact event. Tektites are silica rich (roughly rhyolitic), extremely dry, and often contain both lechatelierite inclusions (amorphous SiO2) and flow textures (schlieren) and are an impact product of particular interest to this study. Tektites likely form either very early in the impact process or within the impact plume itself as condensates, and therefore offer a unique insight into the early stages of the impact cratering process. Here, we present both the results of the statistical analysis of published tektite geochemistry and the geochemical analysis of a variety of glasses produced in an aerodynamic levitation laser furnace. The major findings of the statistical analysis are that the variance of tektite geochemistry is broadly controlled by MgO, CaO, K2O, and Na2O, that the Australasian strewn field (an extensive region of tektite distribution) is best subdivided into five geochemical subgroups, and that random forest classification models can predict the strewn field or geochemical subgroup of an unknown tektite with >94% accuracy. In terms of our heating experiments, in nearly all cases, Na2O and K2O are rapidly lost from the melt due to evaporation, while Al2O3, CaO, and TiO2 become progressively enriched. Volatility is far more dependent on peak heating temperature than on heating time. Additionally, the chemical constituents of basalts are less readily volatilized than those of rhyolites or loess, with few exceptions. We also find that the volatility of the chemical constituents of non-standard samples is far more variable than for standard samples and that oxygen fugacity has a strong influence over elemental volatility in the aerodynamic levitation laser furnace. Changes in oxygen fugacity can either result in variable, exaggerated, or even opposite volatility trends depending on the material and oxide in question.

(Bulk) metallic glasses ((B)MGs) are known to exhibit the highest yield strength of any metallic material (up to 5GPa), and show an elastic strain at ambient conditions, which is about ten times larger than that of crystalline materials. Despite these intriguing mechanical properties, BMGs are not used as structural materials in service, so far. The major obstacle is their inherent brittleness, which results from severe strain localization in so-called shear bands. MGs fail due to formation and propagation of shear bands. A very effective way to attenuate the brittle behaviour is to incorporate crystals into the glass. The resulting BMG composites exhibit high strength as well as plasticity. Cu-Zr-Al-based BMG composites are special to that effect, since they combine high strength, plasticity and work-hardening. They are comprised of the glass and shape-memory B2 CuZr crystals, which can undergo a deformation-induced martensitic transformation. The work-hardening originates from the martensitic transformation and overcompensates the work-softening of the glass. The extent of the plasticity of BMG composites depends on the volume fraction, size and particularly on the distribution of the B2 CuZr crystals. Nowadays, it is very difficult, if not impossible to prepare BMG composites with uniformly distributed crystals in a reproducible manner by melt-quenching, which is the standard preparation method. Flash-annealing of BMGs represents a new approach to overcome this deficiency in the preparation of BMG composites and is the topic of the current thesis. Cu46Zr46Al8 and Cu44Zr44Al8Hf2Co2 BMGs were flash-annealed and afterwards investigated in terms of phase formation, crystallization kinetics and mechanical properties. Flash-annealing is a process, which is characterized by the rapid heating of BMGs to predefined temperatures followed by instantaneous quenching. A temperature-controlled device was succesfully developed and built. The Cu-Zr-Al-based BMGs can be heated at rates ranging between 16 K/s and about 200 K/s to temperatues above their melting point. Rapid heating is followed by immediate quenching where cooling rates of the order of 1000 K/s are achieved. As a BMG is flash-annealed, it passes the glass-transition temperature, Tg, and transforms to a supercooled liquid. Further heating leads to its crystallization and the respective temperature, the crystallization temperature, Tx, divides the flash-annealing of BMGs into two regimes: (1) sub-Tx-annealing and (2) crystallization. The structure of the glass exhibits free volume enhanced regions (FERs) and quenched-in nuclei. Flash-annealing affects both heterogeneities and hence the structural state of the glass. FERs appear to be small nanoscale regions and they can serve as initiation sites for shear bands. Flash-annealing of Cu-Zr-Al-based BMGs to temperatures below Tg leads to structural relaxation, the annihilation of FERs and the BMG embrittles. In contrast, the BMG rejuvenates, when flash-annealed to temperatures of the supercooled liquid region (SLR). Rejuvenation is associated with the creation of FERs. Compared to the as-cast state, rejuvenated BMGs show an improved plasticity, due to a proliferation of shear bands, which are the carrier of plasticity in MGs. Flash-annealing enables to probe the influence of the free volume in bulk samples on their mechanical properties, which could not be studied, yet. In addition, B2 CuZr nanocrystals precipitate during the deformation of flash-annealed Cu44Zr44Al8Hf2Co2 BMGs. Deformation-induced nanocrystallization does not occur for the present as-cast BMGs. Flash-annealing appears to stimulate the growth of quenched-in nuclei, which are subcritical in size and can also dissolve, once the BMG is heated to temperatures in the SLR. Rejuvenation represents a disordering process, whereas the growth of quenched-in nuclei is associated with ordering. There is a competition between both processes during flash-annealing. The ordering seems to lead to a “B2-like” clustering of the medium range of Cu44Zr44Al8Hf2Co2 BMGs with increasing heating duration. So far, there does not exist another method to manipulate the MRO of BMGs. If Cu44Zr44Al8Hf2Co2 BMGs are flash-annealed to temperatures near Tx, most likely compressive resiudal stresses develop near the surface, which is cooled faster than the interior of the BMG specimen. They hinder the propagation of shear bands and increase the plasticity of flash-annealed BMGs in addition to rejuvenation and deformation-induced nanocrystallization. If BMGs are heated to temperatures above Tx, they start to crystallize. Depending on the exact temperature to which the BMG is flash-annealed and subsequently quenched, one can induce controlled partial crystallization. Consequently, BMG composites can be prepared. Both Cu-Zr-Al-based BMGs are flash-annealed at various heating rates to study the phase formation as a function of the heating rate. In addition, Tg and Tx are identified for each heating rate, so that a continuous heating transformation diagram is constructed for both glass-forming compositions. An increasing heating rate kinetically constrains the crystallization process, which changes from eutectic (Cu10Zr7 and CuZr2) to polymorphic (B2 CuZr). If the Cu-Zr-Al-based BMGs are heated above a critical heating rate, exclusively B2CuZr crystals precipitate, which are metastable at these temperatures. Thus, flash-annealing of Cu46Zr46Al8 and Cu44Zr44Al8Hf2Co2 BMGs followed by quenching enables the preparation of B2 CuZr BMG composites. The B2 precipitates are small, high in number and uniformly distributed when compared to conventional BMG composites prepared by melt-quenching. Such composite microstructures allow the direct observation of crystal sizes and numbers, so that crystallization kinetics of deeply supercooled liquids can be studied as they are flash-annealed. The nucleation kinetics of devitrified metallic glass significantly diverge from the steady-state and at high heating rates above 90 K/s transient nucleation effects become evident. This transient nucleation phenomenon is studied experimentally for the first time in the current thesis. Once supercritical nuclei are present, they begin to grow. The crystallization temperature, which depends on the heating rate, determines the crystal growth rate. At a later stage of crystallization a thermal front traverses the BMG specimen. In levitation experiments, this thermal front is taken as the solid-liquid interface and its velocity as the steady-state crystal growth rate. However, the thermal front observed during flash-annealing, propagates through the specimen about a magnitude faster than is known from solidification experiments of levitated supercooled liquids. As microstructural investigations show, crystals are present in the whole specimen, that means far ahead of the thermal front. Therefore, it does not represent the solid-liquid interface and results from the collective growth of crystals in confined volumes. This phenomenon originates from the high density of crystals and becomes evident during the heating of metallic glass. It could be only observed for the first time in the current thesis due to the high temporal resolution of the high-speed camera used. The heating rate and temperature to which the BMG is flash-annealed determine the nucleation rate and the time for growth, respectively. The size and number of B2 CuZr crystals can be deliberately varied. Thus mechanical properties of B2 CuZr BMG composites can be studied as a function of the volume fraction and average distance of B2 particles. Cu44Zr44Al8Hf2Co2 BMG specimens were flash-annealed at a lower and higher heating rate (35 K/s and 180 K/s) to different temperatures above Tx and subsequently subjected to uniaxial compression. BMG composites prepared at higher temperatures show a lower yield strength and larger plastic strain due to the higher crystalline volume fraction. They not only exhibit plasticity in uniaxial compression, but also ductility in tension as a preliminary experiment demonstrates. Furthermore, nanocrystals precipitate in the amorphous matrix of BMG composites during deformation. They grow deformation-induced from quenched-in nuclei, which are stimulated during flash-annealing. In essence, flash-annealing of BMGs is capable of giving insight into most fundamental scientific questions. It provides a deeper understanding of how annealing affects the structural state of metallic glasses. The number and size of structural heterogeneities can be adjusted to prepare BMGs with improved plasticity. Furthermore, crystallization kinetics of liquids can be studied as they are rapidly heated. Transient nucleation effects arise during rapid heating of BMGs and they cannot be described using the steady-state nucleation rate. Therefore, an effective nucleation rate was introduced. Besides, the flash-annealing process rises the application potential of BMGs. The microstructure of BMG composites comprised of uniformly distributed crystals and the glass, can be reliably tailored. Thus, flash-annealing constitutes a novel method to design the mechanical properties of BMG composites in a reproducible manner for the first time. BMG composites, which exhibit high strength, large plasticitiy and as in the case of B2 CuZr BMG composites as well work-hardening behaviour, can be prepared, so that the intrinsic brittleness of monolithic BMGs is effectively overcome.

The glass-forming composition ranges in Al-La-Ni and Mg-TM (Cu, Zn)-Y alloys were predicted using Miedema’s model. Glass-forming abilities of Al-La-Ni alloys and Mg-Cu-RE alloys were studied in terms of reduced glass transition temperature (Trg), supercooled liquid region (∆Tx) and γ parameters. The glass-forming ability parameters of Mg-Cu-RE (RE: rare-earth) alloys were correlated with Mendeleev number. The Miedema model has been used to determine glass-forming composition range in binary Al-La, Al-Ni and La-Ni alloy systems and the ternary Al-La-Ni system by neglecting the ternary interactions. The glass-forming composition range for Al-La, Al-Ni and La-Ni alloy systems extends from 5 to 90 at% La, 30 to 80 at% Ni and 5 to 95 at% Ni, respectively. In these systems the predicted glass-forming composition range is wider than the experimentally observed range. Miedema model, restricting the difference of enthalpy of formation between the amorphous and solid solution phases to within –10000 J/mole to –55000 J/mole gives rise to better prediction of glass-forming composition range compared to the original models. The concept of mixing enthalpy and mismatch entropy has been used in order to quantify Inoue’s criteria of glass formation. The mixing enthalpy and normalised mismatch entropy of the ternary Al-La-Ni alloys, calculated by the extended regular solution model, vary between –12 to –40 kJ/mol and 0.16 to 0.65, respectively. The enthalpy contour plot has been constructed to distinguish the glass-forming compositions on the basis of the increasing negative enthalpy of the composition. Six Al rich Al-La-Ni alloys with nominal compositions Al89La6Ni5, Al85La10Ni5, Al85La5Ni10, Al82La8Ni10, Al80La10Ni10 and Al60La20Ni20 three La rich Al-La-Ni alloys with nominal compositions Al34La33Ni33, Al40La40Ni20 and Al25La50Ni25 have been chosen from the Al-La-Ni ternary phase diagram, to study the glass-forming ability of Al-La-Ni ternary alloy system and the correlation between La-based and Al-based glasses. All the alloys have been prepared using arc melting unit. All the alloy ribbons have been prepared using single-wheel vacuum melt-spinning unit. Two different wheel speeds of 20 m/s and 40 m/s were used for preparing ribbons of all the nine alloys. All the Al-La-Ni compositions, excluding equi-atomic composition (Al34La33Ni33) and Al60La20Ni20, give rise to amorphous phases. The supercooled liquid region and reduced glass transition temperature of this system increases with a decrease in Al content and an increase in La content. The glass-forming ability of the Al rich Al-La-Ni alloys is lower than that of the La-rich Al-La-Ni alloys. The glass-forming ability has been explained by taking into account the binary heat of mixing and the atomic radius mismatch of the constituent elements. Preferential crystallisation takes place during the heat treatment of glassy ribbons. The crystalline products are partially influenced by composition and binary heat of mixing between elements. Mg65Cu25Y10 alloy is a classical glass former of a family of Mg-based alloys. The partial or complete substitution of Y with other rare earth elements has been introduced to correlate the Mendeleev Number with the glass-forming ability parameters: reduced glass transition temperatures (Trg = Tg/Tl), supercooled liquid regions (∆Tx = Tx – Tg) and γ-criterion (TX/(Tg + Tm)). Mg-Cu-RE alloys with nominal compositions Mg65Cu25Y10, Mg65Cu25Y5Gd5, Mg65Cu25Y5Nd5, Mg65Cu25Gd10 and Mg65Cu25Nd10 were chosen for this work. The high reduced glass transition temperature, wider supercooled liquid region and higher γ value of Mg-Cu-Gd-Y amorphous alloy compared to Mg-Cu-Y and Mg-Cu-Nd-Y systems indicates that Mg-Cu-Gd-Y alloys possess higher glass-forming ability. The devitrification of all Mg-Cu-RE glassy alloys used for this work give rise to Mg2Cu (oF48) phase, which is known as anti-Laves phase. The glass-forming composition range for binary and ternary Mg-Cu-Y systems was calculated using Miedema’s model. The development of accurate methods of prediction of glass-forming ability in metallic systems is an important challenge. Pettifor has pioneered the Structure Mapping approach to binary intermetallics. The Pettifor approach can be adapted to the designing of bulk metallic glasses (BMGs). This method has been used to design Al-based and Mg-based BMG’s. Pettifor introduced an integer parameter to characterize the elements, which he called the Mendeleev Number. Essentially, Pettifor’s scheme orders the elements in a sequence of increasing electronegativity. With respect to Mendeleev Number, the Mg-Cu-RE system can be regarded as a binary system, because of the closeness of Mg and Cu (Mg:73, Cu:72, Y:25, Gd:27 and Nd:30). For this system, Mendeleev Number is a more effective parameter than atomic size (Mg: 1.60 Å, Cu: 1.27 Å), as a predictor of glass-forming ability. The effect of Y and rare earth elements on glass forming ability is similar. The atomic number of Y (39) is away from that of the rare earth elements and the Mendeleev Number of Y (25) comes in between those of the rare earth elements. Mg-Zn-Y system is an interesting system for researchers because of higher strength of these alloys. This system draws the crystallographers’ attention due to its composition-dependent structure variations. The Mg-rich RS/PM Mg-Zn-Y alloys yield superior mechanical properties. Therefore, the Mg-rich Mg-Zn-Y system has been chosen to study the microstructural evolution, even though the theoretical calculations for the glass-forming composition range for the Mg-Zn-Y system shows that this system is not a good glass former. Mg-Zn-Y system with nominal compositions Mg97Zn1Y2, Mg97Zn2Y1, Mg97−xZn1Y2Zrx and Mg92Zn6.5Y1.5 were chosen to study the microstructural evolution of these alloys. A small increase in Zn amount (above 2 at.%) in Mg-rich Mg-Y system results in quasicrystalline particles embedded in the matrix, whereas the addition of Zn up to 2 at.% leads to microstructural changes in the α-Mg solid solution.

Les implants de corps humain biocompatibles à base de Ti de faible module de Young et sans élèments toxiques sont développés dans deux régimes de matériaux, les alliags cristallins à base de Ti-Nb(-Sn) et les alliages amorphes à base de Ti -Fe -Si. Une série d'alliages à base de Ti-Nb(-Sn) a été synthétisée par une aspiration coulée par la moule de cuivre et soumis à différents traitements thermiques (refroidissement du four ou trempe à l'eau). La microstructure, les propriétés thermiques et mécaniques des échantillons traités telles que la coulée et la chaleur ont été étudiées. On montre que l'addition de Sn augmente la stabilité de la phase β. Les modules de Young de ces alliages ont été également mesurés avec des mesures par ultrasons. Les alliages Ti74Nb26 trempés à l'eau avaient le plus faible module de Young. L'addition de Sn a peu d'impact sur le module de Young des alliages Ti-Nb. Les alliages amorphes à base de Ti- Fe-Si ont été synthétisés par filage à l'état fondu. La capacité de formation des verres, les propriétés thermiques et les propriétés de corrosion des alliages à base de Ti- Fe-Si ont été étudiées. La composition vitreuse a été conçue en fonction de la règle de l'eutectique profond. On a constaté que la région la plus proche du point eutectique ternaire(Ti65Fe30Si5) est une région quasi-cristalline icosaédrique, tandis que le côté plus raide (Si côté riche) de ce point eutectique ternaire est la région de formation de verre. L'effet de L'addition élémentaire mineur (Ge, Pd, Zr) sur la capacité de formation de verre des alliages à base de Ti- Fe-Si a été également étudié. L'observation in situ d'amorphisation des alliages vitreux Ti40Zr10Cu34Pd14Sn2 en faisceau synchrotron a été effectuée. L'alliage a été vitrifié avec succès dans un appareil à sustentation aérodynamique. / The Ti-based biocompatible human body implants of low Young's modulus and without toxic elements are developed in two regime of materials, crystalline Ti-Nb(-Sn) based alloys and amorphous Ti-Fe-Si based alloys. A series of Ti-Nb(-Sn) alloys were synthesized by copper mould suction casting and subjected to different heat treatments (furnace cooling or water quenching). The microstructure, thermal and mechanical properties of the as-cast and heat treated samples were investigated. It is shown that the addition of Sn increases the stability of the β phase. The Young's moduli of these alloys were also measured by ultrasonic measurements. Water-quenched Ti74Nb26 alloy was found to exhibits the lowest Young's modulus. Sn addition has little impact on the Young's moduli of the TiNb alloys. The Ti-Fe-Si based amorphous alloys were synthesized by melt spinning. The glass forming ability, thermal properties and corrosion properties of Ti-Fe-Si based alloys were investigated. The glassy compositions were designed according to the deep eutectic rule. It was found that the region near ternary eutectic point (Ti65Fe30Si5) is an icosahedral quasicrystal forming region, whereas the steeper side (Si rich side) of this ternary eutectic point is the glass forming region. Effect of minor elemental addition (Ge, Pd, Zr) on glass forming ability of the Ti-Fe-Si based alloys was also studied. The in situ observation of amorphization of Ti40Zr10Cu34Pd14Sn2 glassy alloy in synchrotron beam was conducted. The alloy was successfully vitrified in an aerodynamic levitation apparatus.

The aim of this study is to form a theoretical model for simulation of glass forming ability of Fe &amp / #65533 / Based bulk amorphous alloys, to synthesize Fe &amp / #65533 / based multicomponent glassy alloys by using the predictions of the theoretical study, and to analyze the influence of crystallization and solidification kinetics on the microstructural features of this amorphous alloys. For this purpose, first, glass forming ability of Fe &amp / #65533 / (Mo, B, Cr, Nb, C) &amp / #65533 / X ( X = various alloying elements, selected from the periodic table) ternary alloy systems were simulated for twenty different alloy compositions by using the electronic theory of alloys in pseudopotential approximation and regular solution theory. Then, by using the results of the theoretical study, systematic casting experiments were performed by using centrifugal casting method. The alloying elements were melted with induction under argon atmosphere in alumina crucibles and casted into copper molds of different shapes. Characterization of the cast specimens were performed by using DSC, XRD, SEM, and optical microscopy. Comparison of equilibrium and nonequilibrium solidification structures of cast specimens were also performed so as to verify the existence of the amorphous phase. Good agreement of the results of experimental work, with the predictions of the theoretical study, and the related literature was obtained.

(Bulk) metallic glasses ((B)MGs) are known to exhibit the highest yield strength of any metallic material (up to 5GPa), and show an elastic strain at ambient conditions, which is about ten times larger than that of crystalline materials. Despite these intriguing mechanical properties, BMGs are not used as structural materials in service, so far. The major obstacle is their inherent brittleness, which results from severe strain localization in so-called shear bands. MGs fail due to formation and propagation of shear bands. A very effective way to attenuate the brittle behaviour is to incorporate crystals into the glass. The resulting BMG composites exhibit high strength as well as plasticity. Cu-Zr-Al-based BMG composites are special to that effect, since they combine high strength, plasticity and work-hardening. They are comprised of the glass and shape-memory B2 CuZr crystals, which can undergo a deformation-induced martensitic transformation. The work-hardening originates from the martensitic transformation and overcompensates the work-softening of the glass. The extent of the plasticity of BMG composites depends on the volume fraction, size and particularly on the distribution of the B2 CuZr crystals. Nowadays, it is very difficult, if not impossible to prepare BMG composites with uniformly distributed crystals in a reproducible manner by melt-quenching, which is the standard preparation method. Flash-annealing of BMGs represents a new approach to overcome this deficiency in the preparation of BMG composites and is the topic of the current thesis. Cu46Zr46Al8 and Cu44Zr44Al8Hf2Co2 BMGs were flash-annealed and afterwards investigated in terms of phase formation, crystallization kinetics and mechanical properties. Flash-annealing is a process, which is characterized by the rapid heating of BMGs to predefined temperatures followed by instantaneous quenching. A temperature-controlled device was succesfully developed and built. The Cu-Zr-Al-based BMGs can be heated at rates ranging between 16 K/s and about 200 K/s to temperatues above their melting point. Rapid heating is followed by immediate quenching where cooling rates of the order of 1000 K/s are achieved. As a BMG is flash-annealed, it passes the glass-transition temperature, Tg, and transforms to a supercooled liquid. Further heating leads to its crystallization and the respective temperature, the crystallization temperature, Tx, divides the flash-annealing of BMGs into two regimes: (1) sub-Tx-annealing and (2) crystallization. The structure of the glass exhibits free volume enhanced regions (FERs) and quenched-in nuclei. Flash-annealing affects both heterogeneities and hence the structural state of the glass. FERs appear to be small nanoscale regions and they can serve as initiation sites for shear bands. Flash-annealing of Cu-Zr-Al-based BMGs to temperatures below Tg leads to structural relaxation, the annihilation of FERs and the BMG embrittles. In contrast, the BMG rejuvenates, when flash-annealed to temperatures of the supercooled liquid region (SLR). Rejuvenation is associated with the creation of FERs. Compared to the as-cast state, rejuvenated BMGs show an improved plasticity, due to a proliferation of shear bands, which are the carrier of plasticity in MGs. Flash-annealing enables to probe the influence of the free volume in bulk samples on their mechanical properties, which could not be studied, yet. In addition, B2 CuZr nanocrystals precipitate during the deformation of flash-annealed Cu44Zr44Al8Hf2Co2 BMGs. Deformation-induced nanocrystallization does not occur for the present as-cast BMGs. Flash-annealing appears to stimulate the growth of quenched-in nuclei, which are subcritical in size and can also dissolve, once the BMG is heated to temperatures in the SLR. Rejuvenation represents a disordering process, whereas the growth of quenched-in nuclei is associated with ordering. There is a competition between both processes during flash-annealing. The ordering seems to lead to a “B2-like” clustering of the medium range of Cu44Zr44Al8Hf2Co2 BMGs with increasing heating duration. So far, there does not exist another method to manipulate the MRO of BMGs. If Cu44Zr44Al8Hf2Co2 BMGs are flash-annealed to temperatures near Tx, most likely compressive resiudal stresses develop near the surface, which is cooled faster than the interior of the BMG specimen. They hinder the propagation of shear bands and increase the plasticity of flash-annealed BMGs in addition to rejuvenation and deformation-induced nanocrystallization. If BMGs are heated to temperatures above Tx, they start to crystallize. Depending on the exact temperature to which the BMG is flash-annealed and subsequently quenched, one can induce controlled partial crystallization. Consequently, BMG composites can be prepared. Both Cu-Zr-Al-based BMGs are flash-annealed at various heating rates to study the phase formation as a function of the heating rate. In addition, Tg and Tx are identified for each heating rate, so that a continuous heating transformation diagram is constructed for both glass-forming compositions. An increasing heating rate kinetically constrains the crystallization process, which changes from eutectic (Cu10Zr7 and CuZr2) to polymorphic (B2 CuZr). If the Cu-Zr-Al-based BMGs are heated above a critical heating rate, exclusively B2CuZr crystals precipitate, which are metastable at these temperatures. Thus, flash-annealing of Cu46Zr46Al8 and Cu44Zr44Al8Hf2Co2 BMGs followed by quenching enables the preparation of B2 CuZr BMG composites. The B2 precipitates are small, high in number and uniformly distributed when compared to conventional BMG composites prepared by melt-quenching. Such composite microstructures allow the direct observation of crystal sizes and numbers, so that crystallization kinetics of deeply supercooled liquids can be studied as they are flash-annealed. The nucleation kinetics of devitrified metallic glass significantly diverge from the steady-state and at high heating rates above 90 K/s transient nucleation effects become evident. This transient nucleation phenomenon is studied experimentally for the first time in the current thesis. Once supercritical nuclei are present, they begin to grow. The crystallization temperature, which depends on the heating rate, determines the crystal growth rate. At a later stage of crystallization a thermal front traverses the BMG specimen. In levitation experiments, this thermal front is taken as the solid-liquid interface and its velocity as the steady-state crystal growth rate. However, the thermal front observed during flash-annealing, propagates through the specimen about a magnitude faster than is known from solidification experiments of levitated supercooled liquids. As microstructural investigations show, crystals are present in the whole specimen, that means far ahead of the thermal front. Therefore, it does not represent the solid-liquid interface and results from the collective growth of crystals in confined volumes. This phenomenon originates from the high density of crystals and becomes evident during the heating of metallic glass. It could be only observed for the first time in the current thesis due to the high temporal resolution of the high-speed camera used. The heating rate and temperature to which the BMG is flash-annealed determine the nucleation rate and the time for growth, respectively. The size and number of B2 CuZr crystals can be deliberately varied. Thus mechanical properties of B2 CuZr BMG composites can be studied as a function of the volume fraction and average distance of B2 particles. Cu44Zr44Al8Hf2Co2 BMG specimens were flash-annealed at a lower and higher heating rate (35 K/s and 180 K/s) to different temperatures above Tx and subsequently subjected to uniaxial compression. BMG composites prepared at higher temperatures show a lower yield strength and larger plastic strain due to the higher crystalline volume fraction. They not only exhibit plasticity in uniaxial compression, but also ductility in tension as a preliminary experiment demonstrates. Furthermore, nanocrystals precipitate in the amorphous matrix of BMG composites during deformation. They grow deformation-induced from quenched-in nuclei, which are stimulated during flash-annealing. In essence, flash-annealing of BMGs is capable of giving insight into most fundamental scientific questions. It provides a deeper understanding of how annealing affects the structural state of metallic glasses. The number and size of structural heterogeneities can be adjusted to prepare BMGs with improved plasticity. Furthermore, crystallization kinetics of liquids can be studied as they are rapidly heated. Transient nucleation effects arise during rapid heating of BMGs and they cannot be described using the steady-state nucleation rate. Therefore, an effective nucleation rate was introduced. Besides, the flash-annealing process rises the application potential of BMGs. The microstructure of BMG composites comprised of uniformly distributed crystals and the glass, can be reliably tailored. Thus, flash-annealing constitutes a novel method to design the mechanical properties of BMG composites in a reproducible manner for the first time. BMG composites, which exhibit high strength, large plasticitiy and as in the case of B2 CuZr BMG composites as well work-hardening behaviour, can be prepared, so that the intrinsic brittleness of monolithic BMGs is effectively overcome.

No description available.

No description available.