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Title: Quantitatively defining free-volume, interconnecting-zone and cluster in metallic glasses

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Journal Article: Publisher's Accepted Manuscript
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Journal Volume: 57; Journal Issue: C; Related Information: CHORUS Timestamp: 2017-05-29 09:19:16; Journal ID: ISSN 0966-9795
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United Kingdom

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Fan, Cang, Liu, C. T., Chen, G., and Liaw, P. K. Quantitatively defining free-volume, interconnecting-zone and cluster in metallic glasses. United Kingdom: N. p., 2015. Web. doi:10.1016/j.intermet.2014.10.008.
Fan, Cang, Liu, C. T., Chen, G., & Liaw, P. K. Quantitatively defining free-volume, interconnecting-zone and cluster in metallic glasses. United Kingdom. doi:10.1016/j.intermet.2014.10.008.
Fan, Cang, Liu, C. T., Chen, G., and Liaw, P. K. 2015. "Quantitatively defining free-volume, interconnecting-zone and cluster in metallic glasses". United Kingdom. doi:10.1016/j.intermet.2014.10.008.
title = {Quantitatively defining free-volume, interconnecting-zone and cluster in metallic glasses},
author = {Fan, Cang and Liu, C. T. and Chen, G. and Liaw, P. K.},
abstractNote = {},
doi = {10.1016/j.intermet.2014.10.008},
journal = {Intermetallics},
number = C,
volume = 57,
place = {United Kingdom},
year = 2015,
month = 2

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Publisher's Version of Record at 10.1016/j.intermet.2014.10.008

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  • The free volume model for flow in metallic glasses predicts a significant increase in free volume at the onset of plastic deformation. The details of these structural changes are unclear, however, particularly during strain localization in shear bands. In this study, the free volume changes associated with inhomogeneous plastic deformation of a Cu-based bulk metallic glass were examined using positron annihilation spectroscopy (PAS). PAS results indicated that there was a distribution of free volume site sizes in both the as-quenched and rolled glasses, and that the concentration of larger sites increased with deformation. Differential scanning calorimetry (DSC) was also usedmore » to observe the glass transition behaviors of Cu- and Zr-based glasses after rolling and annealing. Annealing resulted in an increase in the height of the endothermic glass transition peak, consistent with structural relaxation relative to the as-quenched material. Deformation resulted in both a lower endothermic peak height and an earlier and deeper exothermic peak associated with structural relaxation, indicating a more disordered structure with more free volume.« less
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  • We show that 30 keV Ar cluster ion bombardment of Ni{sub 52.5}Nb{sub 10}Zr{sub 15}Ti{sub 15}Pt{sub 7.5} metallic glass (MG) can remove surface mountain-like features and reduce the root mean square surface roughness from 12 nm to 0.7 nm. X-ray diffraction analysis reveals no crystallization after cluster ion irradiation. Molecular dynamics simulations show that, although damage cascades lead to local melting, the subsequent quenching rate is a few orders of magnitude higher than the critical cooling rate for MG formation, thus the melted zone retains its amorphous nature down to room temperature. These findings can be applied to obtain ultra-smooth MGsmore » without introducing crystallization.« less
  • Though discovered more than a half century ago metallic glasses remain a scientific enigma. Unlike crystalline metals, characterized by short, medium, and long-range order, in metallic glasses short and medium-range order persist, though long-range order is absent. This fact has prompted research to develop structural descriptions of metallic glasses. Among these are cluster-based models that attribute amorphous structure to the existence of clusters that are incommensurate with crystalline periodicity. Not addressed, however, are the chemical factors stabilizing these clusters and promoting their interconnections. We have found that glass formers are characterized by a rich cluster chemistry that above the glassmore » transformation temperature promotes exchange as well as static and vibronic sharing of atoms between clusters. The vibronic mechanism induces correlated motions between neighboring clusters and we hypothesize that the distance over which these motions are correlated mediates metallic glass stability and influences critical cooling rates.« less
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