Activation energy spectrum for relaxation and polyamorphism in an ultra-viscous metallic glass former

TL;DR

This paper investigates a liquid-liquid transition in an ultra-viscous metallic glass-former during annealing, revealing complex relaxation behaviors and supporting the idea of underlying order-disorder transitions related to liquid fragility.

Contribution

It provides experimental evidence of a liquid-liquid transition in a metallic glass during annealing below Tg, using multiple advanced techniques, and links fragility to underlying structural transitions.

Findings

Identification of a liquid-liquid transition in metallic glass during annealing

Observation of multiple enthalpy recovery decays and aging regimes

Support for the link between fragility and order-disorder transition

Abstract

Many glass-formers exhibit phase transitions between two distinct liquid states. For some metallic glass-formers, the liquid-liquid transition is experimentally found in the supercooled liquid at intermediate temperature between the melting point and the glass transition temperature Tg. We report here on a liquid-liquid transition in an ultra-viscous metallic glass-former, accessed during long-time annealing. This study is conducted on the Au49Cu26.9Si16.3Ag5.5Pd2.3 composition with a liquid-liquid transition temperature slightly lower than Tg. The consequence is that the high-temperature kinetically fragile liquid freezes into the glass during conventional processing and the underlying liquid-liquid transition is thus accessed by the system during annealing below Tg. Upon reheating, the reverse transformation is observed by calorimetry. This conclusion is supported by a broad collection of complementary laboratory and synchrotron-based techniques, such as differential- and fast- scanning calorimetry, and x-ray photon correlation spectroscopy. Our findings support the big-picture proposed by Angell that liquids with different fragility occupy different flanks of an underlying order-disorder transition. Furthermore, our multiscale analysis reveals the existence of multiple decays of the enthalpy recovery, which is reflected in the observed microscopic ordering and aging mechanism of the glass through distinct stationary regimes interconnected by abrupt dynamical aging regimes.