Workflow for a reproducible and accurate determination of free volume in metallic glasses by differential scanning calorimetry

The physical and mechanical properties of metallic glasses can be significantly tuned by controlling their free volume. The change in enthalpy measured by differential scanning calorimetry provides an indirect measure of free volume and thus serves as an important indicator of the structural state. Therefore, reproducible, and comparable methods for quantifying the relaxation enthalpy are becoming increasingly important. In this study, we present a systematic experimental comparison of methods for quantifying relaxation enthalpy in a CuZr-based model metallic glass. Our main objective is to establish a reproducible workflow that accurately quantifies free volume in metallic glasses. We benchmark conventional methods against more precise approaches, including the Three-Step Method. Severe plastic deformation is used to tune the free volume of a metallic glass. Our results show that the Three-Step Method not only gives higher precision but also represents the evolution of free volume during severe plastic deformation better. It is demonstrated that the conventional approach systematically overestimates the relaxation enthalpy by up to a factor of two when benchmarked against the Three-Step Method. Density changes derived indirectly through calorimetry concord very well with directly measured densities using Archimedes' principle across different enthalpic states. It can be concluded that kinetic evaluations and the ability to accurately measure absolute values benefit from a standardized workflow. A more standardized description of the structural state helps tailoring the properties of metallic glasses for advanced applications in microelectronics and information technology, energy storage and conversion systems, biomedicine, aerospace, and consumer products.