Relationship between the shear modulus and volume relaxation in high-entropy metallic glasses: experiment and physical origin

TL;DR

This study investigates the relationship between shear modulus and volume relaxation in high-entropy metallic glasses, revealing that interstitial-type defects significantly influence relaxation behavior across a wide temperature range.

Contribution

It introduces a unified description of relaxation in high-entropy metallic glasses using a single parameter, linking shear modulus and volume changes to interstitial defects.

Findings

Relaxation behavior characterized by a temperature-independent parameter K_i.

Volume relaxation linearly depends on defect concentration.

Interstitial-type defects are identified as primary relaxation sources.

Abstract

We performed parallel measurements of the high-frequency shear modulus $G$ and relative volume $\Delta V/V$ for high-entropy Ti$_{20}$Zr$_{20}$Hf$_{20}$Be$_{20}$Cu$_{20}$ and Ti$_{20}$Zr$_{20}$Hf$_{20}$Be$_{20}$Ni$_{20}$ glasses upon heating from room temperature up to the complete crystallization. The changes of these properties due to structural relaxation both below and above the glass transition temperature are singled out. It is shown that these changes for both initial and preannealed samples can be well described within the framework of the Interstitialcy theory. It is found that the whole relaxation process in the full temperature range of the experiments for both samples' states can be characterized by a single dimensionless temperature-independent parameter $K_i=dln\;G/dln\;V$, which equals to -44 and -53 for the above glasses, respectively, and strongly points at interstitial-type defects as a source of relaxation. We also show that the relaxation of the relative volume linearly depends on the defect concentration. This behavior can be described by another dimensionless temperature-independent parameter, which is related with the relaxation volume of defects. Possible contribution of vacancy-like defects into the relaxation is discussed.