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Arc-melted multiphase intermetallic alloys, Mo76Si14B10, Mo74Si14B10Zr2, Mo79.5Si12B8.5 and Mo77.5Si12B8.5Zr2 with microstructures containing Moss, Mo3Si and Mo5SiB2 were isothermally exposed for 1 h or 24 h at 1000 °C, 1150 °C and 1300 °C in dry or moist air. The residual area fraction was found to be the highest on exposure at 1150 °C in dry air, but the least at this temperature in moist air. Examination of dry air formed oxide scales by X-ray diffraction, and scanning electron microscopy with energy-dispersive spectroscopy showed the presence of Mo, and MoO2 with a continuous, protective glassy B2O3–SiO2 top layer. Formation of Zr(MoO4)2 in the Zr-containing alloys had lowered mass loss by arresting MoO3 vaporization, and had enhanced the B2O3–SiO2 scale formation kinetics. Further, Si(OH)4, cristobalite, H3BO3 and MoO3·(H2O)2 appeared to be constituting the oxidation products formed in moist air. Alloying with Zr enhanced the kinetics of protective scale formation by lowering the Moss content, and microstructural refinement. The deterioration of oxidation resistance in moist air was conjectured to be due to longer duration required for protective scale to form, formation of β-cristobalite permitting grain boundary diffusion of oxygen anions, as well as volatile hydrated oxidation products as mentioned above. Formation of ZrSiO4 and dissolved ZrO2 in B2O3–SiO2 scale of the Mo-Si-B-Zr alloys in both dry air and moist air is considered to have contributed to the enhanced protective character of oxide scale by stabilizing the glassy scale. [ABSTRACT FROM AUTHOR]

We report on the evolution of the atomic-scale strain tensor of ductile Zr64.13Cu15.75Ni10.12Al10 bulk metallic glass under tensile loading by using x-ray synchrotron radiation. The same kind of samples was previously investigated under compressive loading and revealed yielding at 1690 MPa together with large deformability of up to 160% strain. In tension the samples fracture at a lower stress, 1500 MPa, with no sign of yielding or plastic deformation. With no macroplasticity observed under tension, large differences in the elastic constants obtained from the strain tensor and from ultrasonic sound velocity measurements are revealed. This paper presents in detail the measuring procedure as well as the calculation of the tensile tensor and pair distribution functions of Zr64.13Cu15.75Ni10.12Al10 at different stages of deformation. The results are discussed in comparison with other reported data obtained from x-ray diffraction measurements using synchrotron radiation. [ABSTRACT FROM AUTHOR]

Abstract: Mechanical prehistory is an important factor on the stability of the structure, and consideration of this issue is also useful for determining the mechanisms of post-deformation and fracture processes in bulk metallic glasses. We present investigations to reveal the effect of prestraining on the compressive deformation, morphology of the fracture surface and the evolution of microstructural inhomogeneity in Zr44Ti11Cu9.8Ni10.2Be25 (Vitreloy 1b) “brittle” bulk metallic glass (BMG). The intrinsic plasticity of the BMG increases linearly from 0.7% up to 15% plastic strain upon cold rolling up to 30% prestrain at room temperature due to the change of the short-range order of the glassy phase. Regions of river-like patterns appeared on the fracture surface of prestrained BMGs after compression test, which is similar to that appear during tensile deformation indicating the development of a deformation-induced inhomogeneous residual stress distribution. The effect of uniaxial cyclic compression on the flow stress of the as-cast BMG is also investigated. [ABSTRACT FROM AUTHOR]

Abstract: The effect of Al content on the glass formation and mechanical properties was studied for (Cu50Zr50)100−x Al x (x =0, 4, 5, 7) bulk metallic glasses. The crystallization temperatures of fully amorphous Cu50Zr50, Cu48Zr48Al4, Cu47.5Zr47.5Al5 and Cu46.5Zr46.5Al7 as-cast rods are 724K, 753K, 758K and 782K, respectively. The mechanical properties were investigated under compression at room temperature. As-cast Cu46.5Zr46.5Al7 shows the highest yield strength (1867MPa), whereas Cu47.5Zr47.5Al5 shows the largest fracture strain of 11.2%. The fracture surfaces of the compressed samples were investigated by scanning electron microscopy and their morphology has been correlated with the compressive plasticity. [Copyright &y& Elsevier]

Abstract: To circumvent the limited plasticity of bulk metallic glasses (BMGs), heterogeneous materials with glassy matrix and different type and length-scale of heterogeneities (micrometer-sized second phase particles or fibers, nanocrystals in a glassy matrix, phase separated regions, variations in short-range order by clustering) have been reported. We developed bulk metallic glasses and glass matrix composites in martensitic Zr–Cu-base alloys. Large plasticity can be obtained from microstructure consisting of either a glassy structure, or for alloys with martensitic second phase embedded in a glassy matrix. This type of glasses and glass–matrix composites are able to achieve high strength together with pronounced work-hardening. We explore the possibilities to synthesize such in situ composite microstructures based on shape memory alloys (“M-Glasses”) through metal mold casting. [Copyright &y& Elsevier]

Abstract: In the present study we investigate the phase formation and the thermal stability of Cu50Zr50− x Ti x (0≤ x ≤10) and (Cu0.5Zr0.5)100− x Al x glass-forming alloys. Parameters indicating the glass-forming ability (GFA) are calculated from isochronal and isothermal calorimetric experiments. A high Ti content in the Cu–Zr–Ti alloys causes the precipitation of a metastable ternary Laves phase (C15), which does not form in Cu–Zr–Al. Accompanied with it is a significant drop in the activation energy of crystallization. Also the supercooled liquid region (ΔT x = T x − T g), the reduced glass transition temperature (T rg = T g/T liq), and the γ parameter (γ = T x/(T g + T liq)) (T x: crystallization temperature, T g: glass transition temperature and T liq: liquidus temperature) are sensitive to the change in the crystallization sequence. The fragility values calculated are believed to overestimate the GFA of the investigated alloys. Careful selection of the alloy composition enables the targeted precipitation of different crystalline phases. [Copyright &y& Elsevier]

Plastic deformation of Cu–Zr–(Al,Ti) bulk metallic glass (BMG) composites induces a martensitic phase transformation from the B2 to the B19′ CuZr phase. Addition of Ti to binary Cu–Zr increases the temperature above which the B2 CuZr phase becomes stable. This affects the phase formation upon quenching in Cu–Zr–Ti BMG composites. The deformation-induced martensitic transformation is believed to cause the strong work hardening and to contribute to the large compressive deformability with plastic strains up to 15%. [Copyright &y& Elsevier]

We report on distinct variations in local chemistry, structure and length scale of heterogeneous regions in Ti45Cu40Ni7.5Zr5Sn2.5 fully glass rods of different diameters, i.e. rods subjected to different cooling rates. The present investigations indicate that the mechanical properties of the Ti45Cu40Ni7.5Zr5Sn2.5 bulk metallic glass can be modified within a wide range of strength and plastic deformability by controlling the scale of the heterogeneous regions in the glass through appropriate variation of the cooling rate applied for solidification. [ABSTRACT FROM AUTHOR]

Abstract: The combination of high strength with high elastic strain renders bulk metallic glasses (BMGs) or nanostructured Zr-base multicomponent alloys attractive candidates as advanced high-strength materials for structural applications. To circumvent the limited ductility of these glassy alloys, we prepared a heterogeneous microstructure combining glassy or nanostructured matrix along with a dendritic second-phase particles. The alloys were designed by adding different amounts of Nb to the Zr-based multicomponent glass-forming alloy system. The refractory metal Nb promotes the formation of a primary bcc β-Zr phase having dendritic morphology while the residual melt solidifies to a nanostructured/amorphous matrix. A correlation between the alloy composition and adopted casting method with evolved microstructures and mechanical properties is revealed. These composites exhibit a unique combination of high fracture strength up to 1922MPa as well as plastic strain over 15.8% under uni-axial compression testing at room temperature. We emphasize the possibilities to tailor such composite microstructures in favor of either strength or ductility, or a combination of both, and also discuss the acquired ability to synthesize such in situ composite microstructures in bulk form through inexpensive processing routes. [Copyright &y& Elsevier]

A Ti 43 Zr 7 Cu 43 Ni 7 bulk metallic glass (BMG) exhibits a plastic strain of less than 0.2% under room-temperature compression. However, a Ti 45 Zr 5 Cu 40 Ni 7.5 Sn 2.5 BMG developed by addition of Sn to Ti 43 Zr 7 Cu 43 Ni 7 shows a significant improvement of ∼⃒14.8% to the plastic strain with work hardening. Microstructural comparison of these BMGs reveals that the addition of Sn leads to formation of nano-scale chemical heterogeneities throughout the material. These nano-scale chemical fluctuations play an important role in enhancing the plastic strain of (Ti–Cu)-based BMGs. [ABSTRACT FROM AUTHOR]

Abstract: Usually, bulk metallic glasses exhibit strength values superior to conventional crystalline alloys, often combined with a large elastic limit and rather low Young''s modulus. This combination of properties renders such alloys quite unique when compared to commercial materials. However, the major drawback for engineering applications is their limited room temperature ductility and toughness due to the localized deformation processes linked to shear banding, where high plastic deformation is accumulated in a very narrow region without contributing to macroscopic deformation, work hardening or yielding. In this work we report on a new class of metallic glass in a simple Cu-base alloy. Addition of 5at.% Al increases the glass-forming ability of binary Cu50Zr50. The resulting Cu47.5Zr47.5Al5 glass exhibits high strength (2265MPa) together with large room temperature ductility up to 18%. After yielding a strong increase in the flow stress is observed during deformation. The structure of the metallic glass exhibits atomic-scale heterogeneities that enable easy nucleation and continuous multiplication of shear bands. The interaction and intersection of shear bands increases the flow stress of the material with further deformation, leading to a ‘work hardening’-like behavior and yields a continuous rotation of the shear angle up to fracture resulting in a high compressive ductility. [Copyright &y& Elsevier]

The compressive deformation and fracture features of Zr 59 Cu 20 Al 10 Ni 8 Ti 3 bulk metallic glassy samples with aspect ratios in the range of 0.67–2.00 have been investigated. The compressive plastic strain of the glass monotonically increases with decreasing aspect ratio, but the maximum strength almost maintains a constant value of 1.77–1.88  GPa. All the compressive shear-band angles are equal to  ∼⃒40° if modified by the rotation of the primary shear bands. [ABSTRACT FROM AUTHOR]

High-strength in situ composites with enhanced ductility were prepared by various casting methods from Zr–Nb–Cu–Ni–Al alloys related to bulk metallic glass compositions. The composites exhibit a bimodal size distribution consisting of bcc β-Zr dendrites stabilized by the addition of Nb and a nanocrystalline/amorphous matrix. The dendrite and matrix crystallite size and the morphology depend sensitively on casting conditions. The cooling rates estimated from the secondary dendrite arm spacing of the Zr73.5Nb9Cu7Ni1Al9.5 alloy vary between ε≈2.6×103 K/s to 4.0×101 K/s. The effect of processing parameters on the mechanical properties is less significant for the Zr66.4Nb6.4Cu10.5Ni8.7Al8.0 alloy while highly pronounced for the Zr73.5Nb9Cu7Ni1Al9.5 alloy, where optimum properties like fracture stress of 1754 MPa and 17.5% strain to failure were achieved for cast rods 10 mm in diameter. The deformation of the composite proceeds partly through dislocation movement in dendrites and a shear banding mechanism in the nanostructured matrix. [Copyright &y& Elsevier]

In the present work we prepared an in situ Cu47.5Zr47.5Al5 bulk metallic glass matrix composite derived from the shape memory alloy CuZr. We use a strength model, which considers percolation and a three-microstructural-element body approach, to understand the effect of the crystalline phase on the yield stress and the fracture strain under compressive loading, respectively. The intrinsic work-hardenability due to the martensitic transformation of the crystalline phase causes significant work hardening also of the composite material. [ABSTRACT FROM AUTHOR]

Dynamic instability is one of the typical cleavage fracture features in brittle materials. The authors find that dynamic instability of metallic glass starts to occur in the mirror region on the fracture surface through a wavy cracking propagation with the formation of periodic nanoscale steps. This kind of dynamic instability is associated with the early crack curving due to the intrinsic isotropic structure of metallic glass. Furthermore, they classify dynamic instabilities of cleavage fracture as crack curving at low velocity and crack branching at high velocity, corresponding to the mirror and hackle regions of metallic glass, respectively. [ABSTRACT FROM AUTHOR]

Ductile Ti45Cu40Ni7.5Zr5Sn2.5 and Cu47.5Zr47.5Al5 bulk metallic glasses (BMGs) present different work hardening abilities under compression. Microstructural investigations reveal that nanoscale chemical heterogeneities occur throughout the samples. The morphology of the chemically heterogeneous domains in the as-cast Ti45Cu40Ni7.5Zr5Sn2.5 BMG is irregular and significantly interconnected. In contrast, the as-cast Cu47.5Zr47.5Al5 BMG exhibits a spherical morphology of the chemically heterogeneous regions. Furthermore, the distribution of the nanoscale chemical heterogeneity is macroscopically inhomogeneous throughout the material. These findings suggest that the different work hardening abilities of the Ti45Cu40Ni7.5Zr5Sn2.5 and Cu47.5Zr47.5Al5 BMGs possibly originate from the different morphologies and distributions of the chemically heterogeneous regions. [ABSTRACT FROM AUTHOR]

Microstructural investigation of an as-cast Cu47.5Zr47.5Al5 bulk metallic glass (BMG) reveals two amorphous phases formed by liquid phase separation. The morphology of the phase separated amorphous regions is spherical with 10–20 nm in size. These areas are homogeneously distributed throughout the sample. Moreover, a macroscopic heterogeneity also occurs along with the nano-scale liquid phase separation. The macroscopic heterogeneity can be distinguished from the different degree of the chemical fluctuations in the sample, and the existence of nano-scale crystals of less than 5 nm in size. Presumably, both the macroscopic heterogeneity and the nano-scale phase separation enhance branching of the shear bands during deformation in the Cu47.5Zr47.5Al5 BMG. [ABSTRACT FROM AUTHOR]

We report a novel finding of slither propagation of shear bands on the fracture surface of a Cu47.5Zr47.5A15 bulk metallic glass (BMG). The nanoscale heterogeneities in the as-cast state are aggregated along shear bands with irregular morphology. Such heterogeneities create a fluctuating stress field during shear band propagation leading to a slither propagation mode. The slither propagation of 10 to 15 nm wide shear bands is effective to improve both the plasticity and the "work-hardening-like" behavior of BMGs if the size, the morphology, and the elastic properties of the heterogeneities are intimately intercalated during solidification. [ABSTRACT FROM AUTHOR]

The effect of additional elements on microstructure and mechanical properties of (TiCu)-based bulk metallic glasses (BMGs) has been systematically investigated. Based on the values of the heat of mixing between the additional elements and the major constituent elements Ti and Cu, small additions of elements having a positive heat of mixing with Cu and a negative heat of mixing with Ti are effective in forming nanoscale heterogeneities upon solidification and enhance the ductility. It is experimentally demonstrated that the selection of the minor elements in (TiCu)-based BMGs plays a crucial role to induce nanoscale heterogeneities and thus to control the deformation behavior of the bulk metallic glasses. [ABSTRACT FROM AUTHOR]

Cu47.5Zr47.5Al5 was prepared by arc melting and solidified in situ by suction casting into 2-5-mm-diameter rods under various cooling rates (200-2000 K/s). The microstructure was investigated along the length of the rods by electron microscopy, differential scanning calorimetry and mechanical properties were investigated under compression. The microstructure of differently prepared specimens consists of macroscopic spherical shape chemically inhomogeneous regions together with a low volume fraction of randomly distributed CuZr B2 phase embedded in a 2-7 nm size clustered "glassy-martensite" matrix. The as-cast specimens show high yield strength (1721 MPa), pronounced work-hardening behavior up to 2116 MPa and large fracture strain up to 12.1-15.1%. The fracture strain decreases with increasing casting diameter. The presence of chemical inhomogenities and nanoscale "glassy-martensite" features are beneficial for improving the inherent ductility of the metallic glass. [ABSTRACT FROM AUTHOR]

The development of bulk metallic glasses and composites for improving the mechanical properties has occurred with the discovery of many ductile metallic glasses and glass matrix composites with second phase dispersions with different length scales. This article reviews the processing, microstructure development, and resulting mechanical properties of Zr-, Ti-, Cu-, Mg-, Fe-, and Ni-based glassy alloys and also considers the superiority of composite materials containing different phases for enhancing the strength, ductility, and toughness, even leading to a "work-hardening-like" behavior. The morphology, shape, and length scale of the second phase dispersions are crucial for the delocalization of shear bands. The article concludes with some comments regarding future directions of the investigations of spatially inhomogeneous metallic glasses. [ABSTRACT FROM AUTHOR]

The strain rate dependence of plastic deformation of Ce60Al15Cu10Ni15 bulk metallic glass was studied by nanoindentation. Even though the ratio of room temperature to the glass transition temperature was very high (0.72) for this alloy, the plastic deformation was dominated by shear banding under nanoindentation. The alloy exhibited a critical loading rate dependent serrated flow feature. That is, with increasing loading rate, the alloy exhibited a transition from less prominent serrated flow to pronounced serrated flow during continuous loading but from serrated to smoother flow during stepped loading. [ABSTRACT FROM AUTHOR]

The intrinsic plasticity of Zr44Ti11Cu9.8Ni10.2Be25 and Zr55Ti5Al10Cu20 Ni10 bulk metallic glasses (BMGs) are improved from 0.5% up to 15% plastic strain due to the introduction of microstructural inhomogeneities upon cold rolling at room temperature. This approach shows an easy way to overcome the intrinsic brittleness of the BMGs by modifying their physical properties, which enables easy nucleation and branching of multiple shear bands upon unconstrained loading during the compression test. [Copyright &y& Elsevier]

Abstract: Yielding in metallic glasses is often described in terms of the Mohr–Coulomb criterion, τ + μσ ≥ τ 0. It suggests that a material yields when a combination of shear (τ) and normal stresses (σ), linked through the friction coefficient (μ), reaches the critical shear stress (τ 0). In this paper, an increase of the friction coefficient for increasing Poisson ratio is foreseen, if the elastic limit observed under uniaxial (tensile or compressive) and shear stresses remain constant. Experimental values of Young and shear moduli and Poisson ratio of metallic glasses have been collected from the literature. Compressive and tensile yield stresses have been also collected and elastic limits have been calculated. The elastic limit observed under compressive stress decreases with increasing Poisson ratio and it appears similar for metallic glasses based on the same metals. The values of the friction coefficient for metallic glasses have been obtained from the fracture angle observed under uniaxial stress (compressive or tensile) and from the ratio between compressive and tensile strength. Experimental data of the friction coefficient appear rather scattered and a clear trend as a function of Poisson ratio cannot be outlined. The increase of toughness of metallic glasses with increasing Poisson ratio has been ascribed to the corresponding reduction of the compressive elastic limit. [Copyright &y& Elsevier]

Abstract: In situ optimized heat treatment in high-energy monochromatic beam of synchrotron light was conduced to generate fine nanoparticle dispersions in Zr-based alloys. Effect of embedded nanocrystals on the mechanical properties of our BMG-composites was investigated by compressive testing at room temperature. We found that the newly created nanostructured composites show good strength at high ductility with no work hardening. Based on TEM observations, a new mechanism was proposed which compensates for shear softening. The nanocrystals initially smaller than the elementary shear band were expected to growth in active shear band during deformation. [Copyright &y& Elsevier]

Abstract: Ni70Nb30 metallic glass powders were prepared by mechanical alloying and subsequently combined with Al in order to form a metallic glass particle-reinforced Al-based metal matrix composite sintered below the melting temperature of Al by using the powder metallurgy method. The Young’s modulus, yield strength and ultimate strength are all higher than for single-phase pure Al. [Copyright &y& Elsevier]

Abstract: The mechanical behaviour upon compression of (Cu0.50Zr0.50)100−x Al x (x =4, 5, 7) rods with 2 and 3mm diameter was systematically studied and compared with the literature data. Fully amorphous bulk metallic glasses (x =5, 7) show little permanent deformation and reproducible yield stress values. The remarkable fracture strain, observed for some apparently X-ray diffraction amorphous samples (x =4), was found to be due to significant amounts (at least 20%) of the B2-CuZr crystalline phase. The effect of possible flaws on the external surface of the rods was evaluated by mechanical testing of either as cast and machined samples. [Copyright &y& Elsevier]

Abstract: The structural behaviour of Cu50Zr50 and Cu65Zr35 metallic glasses under uniaxial tensile stress was investigated in situ by high-energy X-ray synchrotron diffraction. The components of the elastic strain tensor were determined from both the change of positions of first maximum of the structure factor in reciprocal space as well as from the maxima of the atomic pair correlation function in real space. The atomic scale strain agrees with the macroscopic strain values. The topological and chemical short-range order of the Cu–Zr glasses changes upon loading. The number density of Cu–Zr and Zr–Zr nearest neighbour atomic pair becomes oriented along the loading direction whereas the partial nearest neighbour distances are only weakly influenced. [Copyright &y& Elsevier]

Abstract: Due to their exceptionally high yield strength and yield strain as compared to conventional metallic materials, bulk metallic glasses (BMGs) represent a class of promising engineering materials for structural applications. However, inhomogeneous deformation and severe shear localization at ambient temperature often lead to early failure and limit their reliability as structural materials. Heat treatments around the glass transition temperature (T g) generally aggravate the intrinsic brittleness of BMGs. In this paper, we report on the evolution of a nanoscale inhomogeneous microstructure upon low-temperature annealing in a Zr55Cu30Al10Ni5 BMG. This important outcome is explained by the experimentally observed tendency for chemical decomposition between Cu and Zr of the investigated amorphous system and is in accordance with literature data on various Zr–Cu-based amorphous alloys. Finally, these local fluctuations influence the plasticity of BMGs beneficially, in contrast of the generally accepted embrittlement upon annealing. [Copyright &y& Elsevier]

Abstract: A novel nanostructured Fe–Cr–Mo–Ga–C composite derived from a bulk metallic glass-forming alloy composition has been prepared with different carbon content to improve the ductility of this high-strength material. Excellent compressive mechanical properties were found for both samples, which essentially consist of soft gallium-enriched dendrites embedded in a hard chromium- and molybdenum-enriched matrix. The coexistence of the soft and hard phases leads to a composite material with a high fracture strength combined with large ductility. The obtained values of true strength and true strain are 2.9GPa and 36% for the alloy with lower carbon content and 3.0GPa and 16% for the alloy with higher carbon content, respectively. It is worth noting that such excellent compressive behavior has never been observed before for any crystalline or glassy structured material. [Copyright &y& Elsevier]

A dynamic mechanical softening is observed in a Zr-based bulk glass-forming alloy during nanoindentation. This softening causes a so-called indentation size effect (ISE), i.e. a reduction of strength as the applied load increases. The ISE is more pronounced in the as-cast alloy than in its thermally relaxed state. These observations, together with an increase in the overall hardness after relaxation, are ascribed to the interplay between the annealing-induced reduction of free volume and the creation of excess free volume during deformation. [Copyright &y& Elsevier]

Abstract: We show room temperature plasticity in several ZrCu-based bulk metallic glasses (BMG) after dispersions of crystalline nanoparticles were generated prior to mechanical testing. BMGs are heated in synchrotron light in transmission such that annealing can be interrupted at the very first detection of nucleation of the crystallites. Effect of embedded nanocrystals on the mechanical properties of BMG-Composites was investigated by compressive testing. When nanocrystal dispersions were generated, zirconium–copper-based BMGs that initially showed no plastic deformation prior to fracture, exhibited ductile behavior in compression with about 10% deformation. [Copyright &y& Elsevier]

Abstract: Phase formation in the Cu47Ti33Zr11Ni8Si1 alloy synthesized by various solidification techniques has been studied using X-ray diffraction (XRD), differential scanning calorimetry (DSC) and transmission electron microscopy (TEM) paying, in particular, attention to the TEM sample preparation. While a reduced cooling rate results in a duplex microstructure, consisting of nanocrystals in an amorphous matrix, glass formation is achieved upon employing a faster quenching rate. The difference in composition and quench temperature influence the phase transition upon heating. The essential differences observed in TEM, notwithstanding the ion-milling effects and the different pre-alloy ingots used for metallic glass synthesis, can be linked to differences in the nucleation and growth mechanism which, in turn, is influenced by the chemical short range order (CSRO) obtained upon quenching. [Copyright &y& Elsevier]

Abstract: Ni60Nb40 metallic glass powders were prepared by mechanical alloying and subsequently combined with Al to form an Al–30wt.% Ni60Nb40 metal matrix composite (MMC). The crystallization of the Ni60Nb40 metallic glass reinforcements and their reaction with the Al matrix during preparation of the MMC were investigated in a differential scanning calorimeter (DSC) upon isothermal annealing. The comparison of the DSC curves of the Ni60Nb40 metallic glass and of the Al–30wt.% Ni60Nb40 composite shows that the amorphous Ni60Nb40 particles have a very strong resistance against reaction with Al but reaction occurs after crystallization of the metallic glass. The analysis of the isothermal annealing DSC curves gives an activation energy of crystallization of the Ni60Nb40 metallic glass of 724kJ/mol. The interfacial reaction between Al and the Ni60Nb40 reinforcements is mainly controlled by diffusion. X-ray diffraction (XRD) and scanning electron microscopy (SEM) results indicate that during the interfacial reaction, Ni diffuses from the Ni60Nb40 particles to react with Al and form Al3Ni. At the same time, Al diffuses into the reinforcement particles to react with remaining Nb and form Al3Nb. [Copyright &y& Elsevier]

Abstract: The fracture morphology of Zr-based bulk metallic glass-matrix-composites (BMGCs) and Cu-based bulk metallic glass (BMG) after compression testing has been studied. The quasi-static compression fracture surface displays a mixture of three different distinct patterns: vein-like, smooth featureless and river-like features. The last one corresponds to the morphology known from tensile tests of BMGs. Moreover, randomly distributed transversal steps on the fracture plane are also present. This is in contrast to previous studies where a characteristic vein-like pattern is considered a unique feature of the fracture of BMGs under quasi-static uniaxial compression. The presence of different fracture features indicates that the development of the fracture plane occurs in a stepwise mode. [Copyright &y& Elsevier]