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Open AccessArticle

On the Fragility of Bulk Metallic Glass Forming Liquids

Department of Materials Science and Engineering, Saarland University, Campus C6.3, 66123 Saarbrücken, Germany
Entropy 2017, 19(9), 483;
Received: 25 August 2017 / Revised: 5 September 2017 / Accepted: 7 September 2017 / Published: 10 September 2017
(This article belongs to the Special Issue Thermodynamics in Material Science)
In contrast to pure metals and most non-glass forming alloys, metallic glass-formers are moderately strong liquids in terms of fragility. The notion of fragility of an undercooling liquid reflects the sensitivity of the viscosity of the liquid to temperature changes and describes the degree of departure of the liquid kinetics from the Arrhenius equation. In general, the fragility of metallic glass-formers increases with the complexity of the alloy with differences between the alloy families, e.g., Pd-based alloys being more fragile than Zr-based alloys, which are more fragile than Mg-based alloys. Here, experimental data are assessed for 15 bulk metallic glasses-formers including the novel and technologically important systems based on Ni-Cr-Nb-P-B, Fe-Mo-Ni-Cr-P-C-B, and Au-Ag-Pd-Cu-Si. The data for the equilibrium viscosity are analyzed using the Vogel–Fulcher–Tammann (VFT) equation, the Mauro–Yue–Ellison–Gupta–Allan (MYEGA) equation, and the Adam–Gibbs approach based on specific heat capacity data. An overall larger trend of the excess specific heat for the more fragile supercooled liquids is experimentally observed than for the stronger liquids. Moreover, the stronger the glass, the higher the free enthalpy barrier to cooperative rearrangements is, suggesting the same microscopic origin and rigorously connecting the kinetic and thermodynamic aspects of fragility. View Full-Text
Keywords: bulk metallic glasses; fragility; specific heat capacity; viscosity; configurational entropy; activation energy bulk metallic glasses; fragility; specific heat capacity; viscosity; configurational entropy; activation energy
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Gallino, I. On the Fragility of Bulk Metallic Glass Forming Liquids. Entropy 2017, 19, 483.

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