Probing the microstructure evolution with physical aging in Mg-based metallic glass through nanoindentation and atom probe tomography analyses

Despite decades of research, how glass approaches equilibrium remains a subject of debate in the scientific community. This works aims at characterizing the impact of physical aging on the microstructure and relaxation properties in a magnesium-based metallic glass stored at room temperature for ten years. Calorimetric investigations and X-ray diffraction analyses ensured working on amorphous materials. Then, nanoindentation and atomic probe tomography were used to compare the response of an aged glass with its unaged homologue, in terms of relaxation and chemical structure. Nanoindentation revealed clear differences in terms of length scales associated to atomic rearrangements. The relaxation governed by one main mechanism in an unaged glass evolves towards the coexistence of two main mechanisms with distinct scales of motions. Finally, atom probe tomography mapped the nanoscale chemical and structural evolutions, accompanying the physical aging process. Physical aging manifests by a phase separation, reversible under rejuvenation, which is driven by a mechanism of enrichment/depletion involving the atoms with the highest diffusion coefficients.