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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]

To understand the effect of aluminum addition on the non-equilibrium solidification of the equiatomic CoCrFeNi alloy, the Al 0.3 CoCrFeNi and AlCoCrFeNi high-entropy alloys (HEAs) have been investigated in situ using electromagnetic levitation and high-energy synchrotron X-ray diffraction (XRD). Because the five-component alloys could not be deeply undercooled, the studies were confined to the low undercooling regime. The in situ XRD revealed that a fcc single-phase solid solution is the primary crystalline phase nucleating in Al 0.3 CoCrFeNi melt undercooled up to 80 K. In contrast, the B2 ordered phase appears as the primary phase in the AlCoCrFeNi melt, at least at a low undercooling of about 30 K. These results correlate with the equilibrium phase diagrams available. Crystal growth velocities of the Al 0.3 CoCrFeNi alloy are shown to be smaller than for CrFeNi and CoCrNi equiatomic alloys; nonetheless, they are in the same order of magnitude. Spontaneous grain refinement was observed in the Al 0.3 CoCrFeNi alloy solidified at a low undercooling of Δ T = 70 K. [Display omitted] • In situ non-equilibrium solidification of high-entropy alloys is studied. • Al 0.3 CoCrFeNi alloy shows a sluggish crystal growth, compared to CoCrFeNi. • Spontaneous grain refinement is observed as undercooling of the Al 0.3 CoCrFeNi melt increases. • AlCoCrFeNi forms B2 phase at high temperature and bcc and B2 at room temperature. [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]

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]

The constituent ratio merged into as-fabricated composites can directly influence the content of in-situ formed reinforcing phases, which is closely related to the mechanical performance of these composites. In this work, aluminum matrix composites reinforced with 10, 15, and 20 wt% (ZrC+TiC) ceramic fractions have been manufactured by laser powder bed fusion (LPBF) additive manufacturing. The effect of hybrid ceramic reinforcement content on laser absorption behavior, fabrication and fraction of micro-nanoscale reinforcing phases, mechanical performance of the as-fabricated aluminum matrix composites is studied. In the laser processing, TiC reacts with ZrC to synthesize interfacial layer on the unmolten ceramic particals and precipitate nano-particles. With the hybrid ceramic content raising from 10 to 20 wt%, the laser absorption behavior is enhanced, and the nano-particle fraction increases. The micro/nano hardness of the composites with 20 wt% ceramic content, reaches 120 HV 0.2 and 1.33 GPa, respectively. An elastic modulus of ∼94.4 GPa and tensile strength of ∼280 MPa are obtained for the 15 wt% (ZrC+TiC)/Al composites, much higher than those of the unreinforced Al matrix. This is attributed to the combination of formation of nano-precipitates and coherent bonding at the reinforcement/matrix interfaces in these composites. • (ZrC+TiC)/Al composites with different ceramic contents are fabricated by LPBF. • Spherical and acicular nano-reinforcements in-situ precipitate in the matrix. • A thin transition layer is formed at the unmelted ceramic/matrix interface. • The strengthening mechanism of the (ZrC+TiC)/Al composites is revealed. [ABSTRACT FROM AUTHOR]