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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]

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]

Abstract: A series of Ti–Nb–Ta–(In/Cr) and Ti–Fe–(Sn) alloys containing a bcc β-Ti phase with a grain size ranging from the nanometer/ultrafine regime to the micrometer scale has been prepared by slow cooling from the melt. The plastic deformation behavior has been investigated under compression and the deformation-induced microstructure evolution was checked by X-ray diffraction, scanning and transmission electron microscopy. The data reveal that the underlying mechanisms related to plasticity or brittleness of the β-phase depends significantly on the supersaturation, the local lattice strain, the ease of dislocation slip, as well as twinning and diffusionless transformation triggering grain refinement. The intrinsic structure, the short-range order and the stability of the β-Ti phase have a strong influence on the mode of plastic deformation of the investigated Ti-alloys. [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]

Bulk (Ti0.65Fe0.35)100−x Sn x (x =0, 2.5, 5at.%) ultrafine composites with high strength and plasticity have been prepared. All composites have a hypereutectic microstructure with primary FeTi or/and Ti3Sn phases and a (β-Ti+FeTi) eutectic matrix. The ultrafine composites exhibit a high fracture strength of ∼2350–2650MPa and a large plasticity of ∼7.4–12.5% under compression. The structure of the phases, their refinement and volume fraction are the crucial factors determining the mechanical properties. [Copyright &y& Elsevier]

Abstract: The deformation behavior of multicomponent Ti66Cu8Ni4.8Sn7.2Nb14 composite containing primary dendrites embedded in a nanoeutectic matrix was studied under uniaxial compression. The evolution of slip and shear bands has been investigated at various stages of deformation. This type of advanced composite not only displays a high compressive plasticity of 31.8%, but also exhibits high fracture strength of ≈2.02GPa (true fracture strength 1.38GPa). Pronounced work hardening was observed after yielding. The surface deformation morphology reveals that the work hardening behavior of the composite is related to the plastic deformation of the dendritic phase through slip bands and the interaction of shear bands in the nanostructured matrix with the hardened dendrites. The nucleation of shear band occurs at a certain amount (8%) of plastic deformation at the dendrite–nanoeutectic matrix interface. The final stage of compression proceeds through passing of the shear bands through the work-hardened dendrites into the nanoeutectic matrix, whereby the propagation of the shear bands in the matrix is retarded by the nanoscale phases. [Copyright &y& Elsevier]

Abstract: Systematic investigations of the microstructural changes upon compression have been performed in order to elucidate the microscopic deformation mechanisms of the high-strength and ductile Ti66.1Nb13.9Ni4.8Cu8Sn7.2 nanostructure–dendrite composite. After 8% deformation, a rotation of β-Ti dendrites is observed during the interaction of slip and shear bands. This rotation leads to the formation of new slip bands in the dendrites. The β-Ti dendrites locally transform into ω phase during the interaction between the newly and the previously formed slip bands. The rotation of the dendrites causes local volume changes at the interfacial areas between the dendrites and the matrix, consisting of a mixture of hexagonal close-packed α-Ti and body-centered tetragonal Ti2Cu phases. This induces a rotational stress into the nanostructured matrix. After further deformation up to 25%, the shear bands penetrate the dendrite/matrix interfaces, producing extra interfaces. The nanostructured matrix exhibits a sandwiched microstructure in order to accommodate effectively the shear strains. These results suggest that structural coherency of the dendrite/matrix interfaces is important for controlling both the strength and the ductility of the nanostructure–dendrite composite. [Copyright &y& Elsevier]

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]

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]

We report the microscopic mechanism of lamellae deformation in a series of (Ti 0.705 Fe 0.295 ) 100− x Sn x (0 ⩽ x ⩽ 4) eutectic comprising of ultrafine FeTi and β-Ti phases with varying lamellae thickness. Furthermore, the microstructural refinement and phase rearrangement upon severe forging have been explored using X-ray diffraction and transmission electron microscopy to reveal the dislocation activity inside the lamellae interior and at the β-Ti/FeTi interface. Nanoindentation tests have been performed at control loading rate and control strain rate modes to evaluate the strain rate sensitivity, activation volume, and to compare them with that of the constituent single phases. The strain rate sensitivity slightly decreases upon Sn addition and with the decrease of the lamellar spacing. However, severe forging increases the hardness, reduces the activation volume without any change of the strain rate sensitivity. The role of dislocation accumulation in the ultrafine lamellae, inter-lamellar sliding, formation of sub-boundaries, evolution of shear bands, cutting, and phase rearrangement towards the deformation-induced nanostructuring of the ultrafine lamellar composites, have been discussed using a micromechanical model. [ABSTRACT FROM AUTHOR]