A thermoplastic forming (TPF) map of a Zr 35 Ti 30 Be 26.75 Cu 8.25 bulk metallic glass was constructed through systematic hot-embossing experiments, spanning a wide range of strain rates and temperatures in the supercooled liquid region. By comparison with the corresponding deformation map, it is found that Newtonian flow, non-Newtonian flow and inhomogeneous flow regions correspond well to fully filled, partially filled and non-filled regions, respectively, in the hot-embossing TPF map. Furthermore, the spatio-temporally homogeneous flow facilitates the thermoplastic formabillity of the Zr-based bulk metallic glass, which is rationalized in terms of free volume theory as well as by finite element simulations. Finally, our results are corroborated by potential application tests.

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a b s t r a c tHeterogeneous dynamics in the flow of supercooled metallic liquids are revealed as the oscillated mechanical response in compression and evidenced to be consistent with the range of medium length scales over which structural rearrangements occur detected by small angle X-ray scattering (SAXS) in heating from room temperature to the supercooled liquid region. This range of medium length scales is suggested to be the structural origin of the heterogeneous dynamics of metallic glasses.Ó 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.A non-equilibrium transition from fluidity to rigidity [1], i.e., jamming, prevails in a wide variety of disordered systems [2], including granular media [3], colloidal suspensions [4], molecular systems [5]. While the disordered liquid-like structure remains basically unchanged at the transition, further exploration of the phase space is precluded by the glasslike arrest of their dynamics [1,[6][7][8]. Approaching the jamming limit, the development of heterogeneous atomic dynamics in glasses [2,4,9] is indicated by the structure heterogeneity, i.e., coexistence of liquid-like and solid-like regions [10] of medium length scale (1-3 nm) [11,12]. In situ scattering investigations [13][14][15] have already revealed the critical role played by atomic rearrangements underlying the structure heterogeneity in the flow (i.e., unjamming) of metallic glasses [1]. However, the inherent liquid-like or solid-like local configurations do not correlate well with the heterogeneous atomic rearrangements [16,17], implying that a static view of the structure heterogeneity is not enough to recognize the arrest of dynamics in the fluidity-to-rigidity transition. Rather, unjamming (e.g., flow or glass-to-liquid transition of glasses) and the underlying dynamics would be crucial. In this work, the flow and structure of supercooled metallic liquids are respectively examined via uniaxial compression and in situ small angle X-ray scattering (SAXS) in heating. The range of medium length scales over which structural rearrangements occur observed in SAXS is suggested to be the structural origin of the heterogeneous dynamics of metallic glasses. were carefully prepared to ensure the two ends being parallel. The high temperature compressive stress-strain (SS) curves were obtained above each BMG's T g-end (the end of glass transition temperature) with a Zwick/Roell mechanical testing system. In situ SAXS tests with increasing temperature on Vit106a and Vit1 were conducted at beamline BL16B1 of Shanghai Synchrotron Radiation Facility with a photon energy of 10 keV (wavelength 1.24 Å) to monitor the amorphous structure evolution. Rods of 3 mm in diameter ofThe Fig. 1(a)respectively. All these BMGs show similar stress-strain (SS) r À e responses with increasing strain rates. For example, Fig. 1(a) shows the SS curves for Vit106a. With increasing strain rate, the SS curves change from the stress r increasing monotonously to a plateau at strain rate _ e of an order of 10 À3 s À1, t...

In this work, the effect of alloying an element with positive heat of mixing with Co on the free volume and compressive plasticity of a ZrCoAl bulk metallic glass was investigated. By substituting Co with Cu, fully amorphous rods of 2 mm diameter can be obtained over a wide composition range. With the addition of Cu, the free volume changes from 0.09 to 0.18%, and the fracture plastic strain changes from 1 to 12.4%. However, there is no strong correlation between the free volume and the compressive plasticity. In addition to the free volume content, other factors such as the size, shape and distribution of the free volume sites may also affect the plasticity of BMGs.

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