Relationship between the shear viscosity and heating rate of metallic glasses belowTg

Abstract

It has been shown that the shear viscosity of bulk and ribbon glassy Pd 40 Cu 30 Ni 10 P 20 at temperatures T Ͻ T g ͑T g is the glass transition temperature͒ follows a simple relationship, ln ͑T͒ = B͑T͒ −ln Ṫ , where Ṫ is the heating rate and B depends only on temperature. This means, in particular, that ln ͑T͒ dependencies measured at different heating rates can be superposed by a simple vertical shift and the derivative ‫ץ͉‬ ln / ‫ץ‬ ln Ṫ ͉ T=const = −1. Such a behavior is indeed found for glassy Pd 40 Cu 30 Ni 10 P 20 . The experimental viscosity data derived earlier on other metallic glasses follow the same relationship. It is argued that this relationship originates from stress-oriented irreversible structural relaxation with distributed activation energies.

The kinetics of structural relaxation of bulk and ribbon glassy Pd40Cu30N10P20 monitored by resistance and density measurements

“…One has to accept, therefore, that there should be no thermodynamic driving force for structural (and, consequently, resistance) relaxation by densification of the initial glass. This is also expected to be the case in the viscosity behavior in creep and stress relaxation experiments on Pd 40 Cu 30 Ni 10 P 20 below T g , which is also controlled by the rate structural relaxation [13,14,22]. Indeed, as mentioned above, the viscosities of bulk and ribbon Pd 40 Cu 30 Ni 10 P 20 are pretty much the same (as well as in the case of Zr-based bulk and ribbons glasses, see a review given in Ref.…”

“…However, recent measurements of the shear viscosity g, which is the property most sensitive to structural relaxation below the glass transition temperature T g , showed than g is mainly insensitive to the amount of the free volume (see Refs. [12][13][14] and papers cited therein). This explicitly questions the free volume nature of the relaxation centers ('defects') responsible for structural relaxation in MGs.…”

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

“…As described in detail by Khonik et al 19,20 the viscosity below g T is dependent on the heating rate of the measurement as…”

The recovery of the shear viscosity of thermally aged bulk and ribbon glassy Pd40Cu30Ni10P20 by rapid quenching from the supercooled liquid state

“…13). However, there are a few viscosity non‐isothermal measurements reported for temperatures T < T g 14–17. While η at T ≥ T g is heating rate independent , a strong viscosity heating rate dependence is observed at T ≤ T g 14–17.…”

“…However, there are a few viscosity non‐isothermal measurements reported for temperatures T < T g 14–17. While η at T ≥ T g is heating rate independent , a strong viscosity heating rate dependence is observed at T ≤ T g 14–17. On the other hand, heat treatment of as‐cast MGs below T g is well known to strongly increase the viscosity because of structural relaxation 18.…”