Chemical influence on β-relaxations and the formation of molecule-like metallic glasses

Abstract

Secondary (also known as Johari-Goldstein or b-) relaxations are an intrinsic feature of supercooled liquids and glasses. They are important in many respects but the underlying mechanisms are not well understood. A long-standing puzzle is why some glasses show b-relaxations as pronounced peaks, whereas others as unobvious excess wings. Here we demonstrate that these different behaviours are related to the fluctuations of chemical interactions by using prototypical systems of metallic glasses. A general rule is summarized: pronounced b-relaxations are associated with systems where all the atomic pairs have large similar negative values of enthalpy of mixing, whereas positive or significant fluctuations in enthalpy of mixing suppress b-relaxations. The emerging physical picture is that strong and comparable interactions among all the constituting atoms maintain string-like atomic configurations for the excitations of b-events and can be considered as the formation of molecule-like metallic glasses.

Modeling of the Sub-Tg Relaxation Spectrum of Pd42.5Ni7.5Cu30P20 Metallic Glass

“…This shoulder is associated with a secondary process (β-relaxation) and, although with different degrees of intensity, was observed in all Pd-based alloys 3 . The presence of secondary relaxations has been found in many other metallic glasses 11,12 . In some systems, particularly La-based glasses, a distinguishable secondary relaxation is observed well separated from the α-peak [13][14][15] .…”

Evolution of hidden localized flow during glass-to-liquid transition in metallic glass

“…It is known that the flow phenomenon in MG is the percolation of the localized flow units 12,14,21 . To detect the extreme slow hidden flow before yielding or microscopic structural evolution during GLT, we applied Dynamical Mechanical Spectrum (DMS) measurement, which is a sensitive method to detect the viscoelastic properties of MGs [34][35][36] . The temperature dependence of the loss modulus E 00 measured at 1 Hz is shown in Fig.…”

“…A La 60 Ni 15 Al 25 MG, with excellent glass-forming ability, thermal stability and unusual pronounced b-relaxation behaviour among known MGs 34,35 , is chosen as a model system. Plausible correlations among relaxation behaviours, dynamic heterogeneity, microscopic hidden inhomogeneous flow to macroscopic large-scale homogeneous flow during GLT transition and mechanical behaviours of MGs are established and interpreted by the energy landscape theory.…”

On cryothermal cycling as a method for inducing structural changes in metallic glasses

“…It was also found that Co-based and Fe-based metallic glasses containing metalloid elements exhibit only relaxation behavior upon cryothermal cycling, which has a positive effect on the magnetic properties [50][51][52] . Atomic bonding was found to also be important in β-relaxation processes 53 . β-relaxation processes are directly correlated with the shear transformation zones, and therefore with the plasticity of glasses 54 .…”

“…However, there is still no generally accepted theory for β-relaxation. Yu et al 53 found that β-relaxation is more pronounced in systems with strong bonds between the constituent elements in the alloy system, while positive values or large fluctuations in the values of the enthalpy of mixing suppress β-relaxation.…”