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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: An arc-melted Zr73.5Nb9Cu7Ni1Al9.5 alloy consists of dendritic body-centered cubic solid solution and a mixture of ultrafine body-centered tetragonal Zr2Cu-type and hexagonal close-packed MgZn2-type phases in the ultrafine matrix. This composite exhibits two exothermic reactions upon heating to 973K with a heating rate of 40K/min. After the first exothermic reaction nano-scale ω-phase particles have formed in the β-phase dendrites indicating a decomposition of the supersaturated solid solution upon heating. At the early stage during the decomposition of the β-phase the ω-phase is coherent with the parent phase without clear structural differences. However, semicoherency between the β- and the nano-scale ω-phase regions was observed during the growth of the ω-phase. This structural semicoherency causes nano-scale twinning in the β-phase dendrites around the ordered ω-phase in order to release the mismatch energy at the interfaces between the ordered ω- and β-phases. [Copyright &y& Elsevier]

The effect of Fe addition and the moist environment on the high temperature isothermal oxidation behaviors of multiphase Mo 76- x Si 14 B 10 Fe x (x = 0, 0.5, 1 at.%) composites in the range of 1000–1300 °C have been investigated. The microstructure of all the composites with α–Mo solid solution (SS) and eutectic mixture of Mo 3 Si + Mo 5 SiB 2 phases, has been refined upon Fe addition, which improves the oxidation resistance and reduces the mass loss up to 55% in dry air and 31% in moist air for 24 h exposure. Whereas, the oxidation resistance in moist air improves due to the formation of a protective Fe-rich glassy borosilicate scale, which reduces the vaporization of MoO 3 by forming Fe 2 (MoO 4) 3. The cross-sectional area of the residual alloy for x = 1 were estimated to be 97% in dry air and 85% in moist air that of unoxidized coupons. The bulk hardness of the as-cast composite is 1031 Hv for x = 1, which reduced only by 6.7% (962 Hv) upon oxidation at 1300 °C in both dry and moist air, showing superior stability of the silicide matrix composites for high temperature application. X-ray diffraction, scanning electron microscopy and energy dispersive x-ray spectroscopy studies were performed to identify the various products of oxidation and to explore the mechanism of protection. • Oxidation behaviour of Mo 76- x Si 14 B 10 Fe x at 1000–1300 °C has been studied. • Moist air improves the mass loss by 31% during isothermal oxidation. • Fe addition improves the oxidation resistance in both dry and moist air. [ABSTRACT FROM AUTHOR]

Addition of Fe refines the microstructure of Mo 76-x Si 14 B 10 Fe x ( x = 0, 0.5, 1 at.%) composites containing α-Mo, Mo 3 Si and Mo 5 SiB 2 phases, increases the hardness from 950 Hv ( x = 0) to 1031 Hv ( x = 1), and improves the oxidation resistance at temperature in the range of 800–1300 °C. The hardness of the base alloy substrate decreases only by <7% than that of as-solidified ingots, indicating good microstructural stability of the composite for high temperature application. [ABSTRACT FROM AUTHOR]