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An experimental study of the configurational thermodynamics for a series of near-eutectic Pt80-xCuxP20bulk metallic glass-forming alloys is reported where 14 <x< 27. The undercooled liquid alloys exhibit very high fragility that increases asxdecreases, resulting in an increasingly sharp glass transition. With decreasingx, the extrapolated Kauzmann temperature of the liquid,TK, becomes indistinguishable from the conventionally defined glass transition temperature,Tg. Forx< 17, the observed liquid configurational enthalpy vs.Tdisplays a marked discontinuous drop or latent heat at a well-defined freezing temperature,Tgm. The entropy drop for this first-order liquid/glass transition is approximately two-thirds of the entropy of fusion of the crystallized eutectic alloy. BelowTgm, the configurational entropy of the frozen glass continues to fall rapidly, approaching that of the crystallized eutectic solid in the low T limit. The so-called Kauzmann paradox, with negative liquid entropy (vs. the crystalline state), is averted and the liquid configurational entropy appears to comply with the third law of thermodynamics. Despite their ultrafragile character, the liquids atx= 14 and 16 are bulk glass formers, yielding fully glassy rods up to 2- and 3-mm diameter on water quenching in thin-wall silica tubes. The low Cu content alloys are definitive examples of glasses that exhibit first-order melting.
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Decoupling between calorimetric and dynamical glass transitions in high-entropy metallic glasses
Abstract Glass transition is one of the unresolved critical issues in solid-state physics and materials science, during which a viscous liquid is frozen into a solid or structurally arrested state. On account of the uniform arrested mechanism, the calorimetric glass transition temperature ( T g ) always follows the same trend as the dynamical glass transition (or α -relaxation) temperature ( T α ) determined by dynamic mechanical analysis (DMA). Here, we explored the correlations between the calorimetric and dynamical glass transitions of three prototypical high-entropy metallic glasses (HEMGs) systems. We found that the HEMGs present a depressed dynamical glass transition phenomenon, i.e ., HEMGs with moderate calorimetric T g represent the highest T α and the maximum activation energy of α -relaxation. These decoupled glass transitions from thermal and mechanical measurements reveal the effect of high configurational entropy on the structure and dynamics of supercooled liquids and metallic glasses, which are associated with sluggish diffusion and decreased dynamic and spatial heterogeneities from high mixing entropy. The results have important implications in understanding the entropy effect on the structure and properties of metallic glasses for designing new materials with plenteous physical and mechanical performances.
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- Award ID(s):
- 1804320
- PAR ID:
- 10312955
- Date Published:
- Journal Name:
- Nature Communications
- Volume:
- 12
- Issue:
- 1
- ISSN:
- 2041-1723
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1038/s41467-021-24093-w
