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Metallic glasses exhibit unique mechanical properties. For metallic glass composites (MGC), composed of dispersed nanocrystalline phases in an amorphous matrix, these properties can be enhanced or deteriorated depending on the volume fraction and size distribution of the crystalline phases. Understanding the evolution of crystalline phases during devitrification of bulk metallic glasses upon heating is key to realizing the production of these composites. Here, results are presented from a combination of in situ small‐ and wide‐angle X‐ray scattering (SAXS and WAXS) measurements during heating of Zr‐based metallic glass samples at rates ranging from 102 to 104 Ks−1 with a time resolution of 4ms. By combining a detailed analysis of scattering experiments with numerical simulations, for the first time, it is shown how the amount of oxygen impurities in the samples influences the early stages of devitrification and changes the dominant nucleation mechanism from homogeneous to heterogeneous. During melting, the oxygen rich phase becomes the dominant crystalline phase whereas the main phases dissolve. The approach used in this study is well suited for investigation of rapid phase evolution during devitrification, which is important for the development of MGC. [ABSTRACT FROM AUTHOR]

A combination of complementary high-energy X-ray diffraction, containerless solidification during electromagnetic levitation and transmission electron microscopy is used to map in situ the phase evolution in a prototype Cu-Zr-Al glass during flash-annealing imposed at a rate ranging from 102 to 103 K s−1 and during cooling from the liquid state. Such a combination of experimental techniques provides hitherto inaccessible insight into the phase-transformation mechanism and its kinetics with high temporal resolution over the entire temperature range of the existence of the supercooled liquid. On flash-annealing, most of the formed phases represent transient (metastable) states – they crystallographically conform to their equilibrium phases but the compositions, revealed by atom probe tomography, are different. It is only the B2 CuZr phase which is represented by its equilibrium composition, and its growth is facilitated by a kinetic mechanism of Al partitioning; Al-rich precipitates of less than 10 nm in a diameter are revealed. In this work, the kinetic and chemical conditions of the high propensity of the glass for the B2 phase formation are formulated, and the multi-technique approach can be applied to map phase transformations in other metallic-glass-forming systems. The competition between the formation of different phases and their kinetics need to be clearly understood to make materials with on-demand and multifaceted properties. Here, the authors reveal, by a combination of complementary in situ techniques, the mechanism of a Cu-Zr-Al metallic glass's high propensity for metastable phase formation, which is partially through a kinetic mechanism of Al partitioning. [ABSTRACT FROM AUTHOR]

Details of fast-resistive-heating setups, controlled heating ranging from ∼101 K s−1 to ∼103 K s−1, to study in situ phase transformations (on heating and on cooling) in metallic glasses by high-energy synchrotron x-ray diffraction are discussed. Both setups were designed and custom built at the Leibniz Institute for Solid State and Materials Research Dresden (IFW Dresden) and have been implemented at the P02.1 Powder Diffraction and Total Scattering Beamline and the P21.1 Swedish Materials Science Beamline at PETRA III storage ring, DESY, Hamburg. The devices are interchangeable at both beamlines. Joule heating is triggered automatically and is timed with the incident beam and detector. The crystallization process can be controlled via a feedback circuit by monitoring the change in the time-dependent resistivity and temperature of glasses. Different ambient atmospheres, such as vacuum and inert gases (He and Ar), can be used to control oxidation and cooling. The main focus of these devices is on understanding the crystallization mechanism and kinetics in metallic glasses, which are brittle and for which fast heating gives defined glass–crystal composites with enhanced plasticity. As an example, phase-transformation sequence(s) in a prototyped Cu–Zr-based metallic glass is described on heating, and a crystalline phase beneficial to the plasticity is identified. [ABSTRACT FROM AUTHOR]

Crystallization of Cu 47.5 Zr 48 Al 4 Co 0.5 metallic glass upon isokinetic and isothermal annealing is studied by conventional and ultrafast differential scanning calorimetry, resistive flash-annealing, and in situ high-energy X-ray diffraction. The fast-heating experiments of Cu 47.5 Zr 48 Al 4 Co 0.5 metallic glass are complemented by in situ high-energy XRD studies of the undercooled liquid by using electromagnetic levitation. The combination of complementary techniques reveals a competition between the Cu 10 Zr 7 , B2 CuZr and τ 4 Cu 2 ZrAl phases crystallization depending on heating rate and shows the specific role of Co alloying. A continuous-heating-transformation diagram for a heating rate exceeding six orders of magnitude, Φ = 0.0833 − 90 000 K s−1, and a time-temperature-transformation diagram are constructed. [Display omitted] [ABSTRACT FROM AUTHOR]

The microstructures and mechanical properties of (Cu0.5Zr0.5)100-xZnx (x = 0, 1.5, 2.5, 4.5, 7, 10, and 14 at. %) bulk metallic glass (BMG) composites were studied. CuZr martensitic crystals together with minor B2 CuZr and amorphous phases dominate the microstructures of the as-quenched samples with low Zn additions (x = 0, 1.5, and 2.5 at. %), while B2 CuZr and amorphous phases being accompanied with minor martensitic crystals form at a higher Zn content (x = 4.5, 7, 10, and 14 at. %). The fabricated Cu-Zr-Zn BMG composites exhibit macroscopically appreciable compressive plastic strain and obvious work-hardening due to the formation of multiple shear bands and the deformation-induced martensitic transformation (MT) within B2 crystals. The present BMG composites could be a good candidate as high-performance structural materials. [ABSTRACT FROM AUTHOR]

Co 61 Ta 6 B 33 , Co 59 Ta 8 B 33 , Co 57 Ta 10 B 33 and Co 53 Ta 10 B 37 bulk metallic glasses (BMGs) exhibit a good combination of the ultra-high fracture strength in the range of about 5.4–6.2 GPa, Vickers hardness of 1459–1653 HV0.2 and plastic strain of 0.3–3.2%, depending on composition. Glass forming-ability and physical properties of Co–Ta–B BMGs are discussed in relationship to the Ta and B content and atomic structure. Crystallization upon isochronal and isothermal annealing is studied using differential scanning calorimetry and X-ray diffraction. A novel crystalline phase with ~Ta 2 Co 15 B 8 or ~TaCo 7 B 4 formula is shown to form upon glass annealing. The incubation time for isothermal crystallization in the supercooled liquid state near T g is supposed to be sufficient for thermoplastic forming of Co–Ta–B BMGs. ga1 • Co–Ta–B BMGs with ultrahigh strength and ductility in compression tests. • High glass transition temperature and large supercooled liquid region. • Incubation time for crystallization sufficient for thermoplastic forming. • Novel boride with ~Ta 2 Co 15 B 8 or ~TaCo 7 B 4 unit formula found. [ABSTRACT FROM AUTHOR]

Flash Joule-heating was applied to the Cu47.5Zr47.5Al5 metallic glass for designing fully crystalline metastable nanocomposites consisting of the metastable B2 CuZr and low-temperature equilibrium Cu10Zr7 phases. The onset of crystallization was in situ controlled by monitoring resistivity changes in the samples. The effect of heating rate and annealing time on the volume fraction of the crystalline phases and mechanical properties of the nanocomposites was studied in detail. Particularly, an increase of the heating rate and a decrease of the annealing time lead to a lower number of equilibrium Cu10Zr7 precipitates and an increase of tensile ductility. Tailoring of these non-equilibrium microstructures and mechanical properties may not be possible unless one starts with a fully glassy material that opens new perspectives for designing metastable nanomaterials with unique physical properties. [ABSTRACT FROM AUTHOR]

A combination of conventional calorimetry, ultra-fast scanning calorimetry and resistive heating gives access to heating rates exceeding 6 orders of magnitude allowing to probe crystallization kinetics and mechanisms in a Cu-Zr-Al metallic glass. Continuous-heating-transformation and double-peak time-temperature-transformation diagrams are constructed and related to the formation of glass–crystal composites with enhanced ductility. The metastable B2-CuZr phase becomes dominantly formed at a heating rate of ~102 K s−1 and higher. A critical heating rate to bypass crystallization is ~10,000 K s−1. For isothermal annealing at >850 K, only one crystallization event is detected; for lower temperatures, a complex two-step transformation occurs. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Despite recent progress in understanding the outstanding role of shear bands in plastic deformation of metallic glasses, the details of structural changes in the shear-induced zone is not yet known. In order to probe such changes, we determined the distribution of residual strains at short- and medium-range order around a single shear band in cold-rolled Vit105 bulk metallic glass using a nano-focused high energy X-ray beam. Plastic deformation results in significant residual normal and shear strains at distances of more than 15 μm around the shear band. Based on a detailed analysis of the distribution profile, the magnitude and the direction of the residual shear strain, it is suggested that the shear strain plays a dominant role, compared to the normal strains, for triggering nucleation of further shear bands from a mature shear band. [ABSTRACT FROM AUTHOR]

Fully amorphous rods with diameters up to 2 mm diameter were obtained upon 0.5 at.% Cu addition to the Fe 36 Co 36 B 19.2 Si 4.8 Nb 4 bulk metallic glass. The Cu-added glass shows a very good thermal stability but, in comparison with the Cu-free base alloy, the entire crystallization behavior is drastically changed. Upon heating, the glassy (Fe 36 Co 36 B 19.2 Si 4.8 Nb 4 ) 99.5 Cu 0.5 samples show two glass transitions-like events, separated by an interval of more than 100 K, in between which a bcc-(Fe,Co) solid solution is formed. The soft magnetic properties are preserved upon Cu-addition and the samples show a saturation magnetization of 1.1 T combined with less than 2 A/m coercivity. The relaxation behavior prior to crystallization, as well as the crystallization behavior, were studied by time-resolved X-ray diffraction using synchrotron radiation. It was found that both glassy alloys behave similar at temperatures below the glass transition. Irreversible structural transformations take place when approaching the glass transition and in the supercooled liquid region. [ABSTRACT FROM AUTHOR]

Development of the two-phase bulk metallic glasses (BMGs) is essentially retarded due to difficulties in finding of phase-separated (immiscible) alloys with high glass-forming ability (GFA) of coexistent phases. Referring to the concept of solute partitioning and minimization of free energy, in this work we present an idea that a metallic liquid system containing two liquids with individual self-assembled eutectic composition may yield two-phase BMGs upon casting. The formation of the two-glass structure is discussed and a strategy of partial substitution of chemically similar elements for overcoming the drawback of low GFA is proposed. A family of two-phase zirconium–lanthanide based metallic glasses in bulk form is developed. The mechanical behavior of the two-phase BMGs with different ratio of zirconium-rich to lanthanide-rich glassy phase is studied for the first time. This work provides a new concept for fabrication of two-phase BMGs and reveals the role of constituent phases in determining the mechanical properties of the whole glass. [ABSTRACT FROM AUTHOR]

The martensitic transformation within B2 phase plays a critical role for the ductility of CuZr-based bulk metallic glass (BMG) composites, yet the underlying mechanism for the martensitic transformation process needs further investigations. Here, we found that the onset temperature of the thermally-activated martensitic transformation for CuZr-based BMG composites was reduced to 162.7 ± 2.5 K, which is far lower than those of polycrystalline samples, due to the stabilization of the austenitic phase induced by crystalline-amorphous interfaces. In situ high-energy X-ray diffraction measurements (HEXRD) further demonstrate that the thermally-activated martensitic transformation is governed by an extremely incomplete martensitic transformation from B2 to B19' and B33 phases without the decomposition of B2 phase which generally appears in polycrystalline samples. Due to unconfined stress states during the thermally-activated martensitic transformation, B33 phase forms more early during thermal process than deformation process. The present study provides a further understanding on the martensitic transformation behaviors of shape memory type CuZr-based BMG composites. Image 1 • In situ observations on thermally-activated martensitic transformation for BMG composites was conducted. • Martensitic transformation temperature is far below room temperature. • Extremely incomplete martensitic transformation was observed. • Decomposition of B2 phase does not appear during martensitic transformation. • B33 phase forms earlier during thermal process than deformation process. [ABSTRACT FROM AUTHOR]

A density variation in shear bands visible by electron microscopy is correlated with compositionally altered locations measured by atom-probe tomography in plastically-deformed Al 85.6 Y 7.5 Fe 5.8 metallic-glass ribbons. Two compositionally distinct regions are identified along shear bands, one is Al-rich (~92 at.%), the other is Al-depleted (~82.5 at.%) and both regions show marginal concentration fluctuations of Y and Fe. The elemental re-distribution is observed within shear bands only, and no chemical exchange with the surrounding glassy matrix is observed. Unlabelled Image [ABSTRACT FROM AUTHOR]

Abstract The structure of Ge x Te 100- x (x = 14.5, 18.7, 23.6) glasses prepared by twin roller quenching technique was investigated by neutron diffraction, X-ray diffraction and Ge-K-edge X-ray absorption spectroscopy measurements. Large scale structural models were obtained for each composition by fitting the experimental datasets in the framework of the reverse Monte Carlo technique. It was found that the majority of Ge and Te atoms satisfy the 8-N rule. Simulation results indicate that Ge-Ge bonding is not significant for x = 14.5 and 18.7. The shape and position of the first peak of the Ge-Ge partial pair correlation function evidence the presence of corner sharing tetrahedra already in compositions (x = 14.5 and 18.7) where 'sharing' of a Te atom by two Ge atoms could be avoided due to the low concentration of Ge. Graphical abstract Image 1 Highlights • The average coordination numbers of Ge and Te are close to 4 and 2, respectively. • Corner sharing tetrahedra can be found already in Ge14.5Te85.5. • No Ge-Ge bonds are found during the fitting of diffraction and EXAFS data of Ge14.5Te85.5 and Ge18.7Te81.3. [ABSTRACT FROM AUTHOR]

The crystallization mechanism and solid-state phase transformations in Cu 46.5 Zr 48 Al 4 Nb 1.5 metallic glass upon isokinetic and isothermal annealing are studied by using conventional and fast-scanning differential calorimetry, electric current flash-annealing, electromagnetic levitation, and in-situ high-energy synchrotron X-ray diffraction. Continuous-heating-transformation and time-temperature-transformation diagrams mapping the formation and evolution of the Cu 10 Zr 7 , B2 CuZr, τ 3 Zr 51 Cu 28 Al 21 and τ 4 Cu 2 ZrAl phases in dependence on heating rate and temperature are constructed. Cu 46.5 Zr 48 Al 4 Nb 1.5 metallic glass shows an increased propensity for the Cu 10 Zr 7 phase formation compared to the parent Cu 47.5 Zr 47.5 Al 5 glass. • Crystallization of Cu 46.5 Zr 48 Al 4 Nb 1.5 metallic glass upon flash-annealing is studied. • Processing parameters for fabrication of glass-matrix composites are established. • Nb-microalloying enhances formation of Cu 10 Zr 7 phase upon annealing. • B2 CuZr is always primary phase by crystallization from undercooled liquid. [ABSTRACT FROM AUTHOR]

Abstract: The influence of ball milling on the atomic structure and magnetic properties of the Co40Fe22Ta8B30 metallic glass with a high thermal stability and excellent soft magnetic properties has been investigated. After 14h of milling, the obtained powders were found to consist mainly of an amorphous phase and a small fraction of the (Co,Fe)21Ta2B6 nanocrystals. The changes in the reduced pair correlation functions suggest noticeable changes in the atomic structure of the amorphous upon ball milling. Furthermore, it has been shown that milling is accompanied by introduction of compressive and dilatational sites in the glassy phase and increasing the fluctuation of the atomic-level hydrostatic stress without affecting the coordination number of the nearest neighbors. Ball milling has decreased the thermal stability and significantly affected the magnetic properties through increasing the saturation magnetization, Curie temperature of the amorphous phase and coercivity. [Copyright &y& Elsevier]

Abstract: In this letter we report about a new melt-spun Co40Fe22Ta8B30 metallic glass with a wide supercooled liquid region of 74K. X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) investigations confirmed that crystallization occurs with significantly longer incubation time during annealing above the glass transition, as compared to the well-known Co43Fe20Ta5.5B31.5 glassy alloy. The new alloy as a good soft magnetic material showed a very low coercivity of 0.8A/m and polarization of 0.5T. The origin of high thermal stability was attributed to the formation of Ta–Ta bonds in the microstructure and the absence or very low quantity of Ta-based units with the composition close to the stoichiometry of the (Co,Fe)21Ta2B6 crystalline phase. [Copyright &y& Elsevier]