Existence of multiple critical cooling rates which generate different types of monolithic metallic glass

Jürgen E K Schawe,Jörg F Löffler

doi:10.1038/s41467-018-07930-3

Jürgen E K Schawe, Jörg F Löffler

Open Access

https://doi.org/10.1038/s41467-018-07930-3

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Journal: Nature Communications	Publication Date: Mar 22, 2019
Citations: 82	License type: open-access

Affiliation: ETH Zurich

Abstract

Via fast differential scanning calorimetry using an Au-based glass as an example, we show that metallic glasses should be classified into two types of amorphous/monolithic glass. The first type, termed self-doped glass (SDG), forms quenched-in nuclei or nucleation precursors upon cooling, whereas in the so-called chemically homogeneous glass (CHG) no quenched-in structures are found. For the Au-based glass investigated, the critical cooling and heating rates for the SDG are 500 K s−1 and 20,000 K s−1, respectively; for the CHG they are 4000 K s−1 and 6000 K s−1. The similarity in the critical rates for CHG, so far not reported in literature, and CHG’s tendency towards stochastic nucleation underline the novelty of this glass state. Identifying different types of metallic glass, as is possible by advanced chip calorimetry, and comparing them with molecular and polymeric systems may help to elaborate a more generalized glass theory and improve metallic glass processing.

Highlights

Via fast differential scanning calorimetry using an Au-based glass as an example, we show that metallic glasses should be classified into two types of amorphous/monolithic glass
In14, one of the authors of this paper reported on the crystallization kinetics of an Au-based bulk metallic glass (Au49Ag5.5Pd2.3Cu26.9Si16.337), and constructed, via isothermal measurements in the millisecond range, complete time–temperature–transformation (TTT) diagrams of crystallization in the undercooled/supercooled liquid range upon cooling and heating
We show that quenchedin nuclei or nucleation precursors form in the self-doped glass (SDG) upon cooling at medium rates, which generates significant differences in the critical cooling and heating rates

Summary

Introduction

Via fast differential scanning calorimetry using an Au-based glass as an example, we show that metallic glasses should be classified into two types of amorphous/monolithic glass. Since the introduction of non-adiabatic chip calorimetry[18,19] and its commercialization[20,21], calorimetric measurements at defined cooling and heating conditions have been possible using fast differential scanning calorimetry (FDSC) This technique is frequently used to study glass transition phenomena and nanostructure formation in polymers[22,23,24], molecular glass formers[25], and chalcogenides[26,27,28,29]. In this study we use a newly developed Flash DSC2+ instrument (see Methods) which allows us to perform calorimetric experiments at ultrafast cooling rates of 40,000 Ks−1 and heating rates greater than 60,000 Ks−1 The latter allows us to upquench a certain phase, where up-quenching denotes a heating process that is so rapid that no structural changes occur before melting of the previously frozen phase[36]

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