When metallic glasses (MGs) are loaded in the elastic/anelastic regime, their energy content increases – as is easily quantified by calorimetry.  The stored energies, as high as 515 J mol^‒1, are significant, amounting to 10% of the heat of fusion of the alloy.  It is natural to associate the stored energy with the work done on the sample.  For MGs, as for polycrystalline metals, 1‒10% of the work done in plastic deformation remains stored in the material.  This paper shows that for loading below the yield stress, the behaviour is dramatically different: the stored energy is as much as 40 times the work done!

This seems to be ‘something for nothing’ ‒ from where does the stored energy come?  This paper provides an understanding of how the energy comes by heat flow from the surroundings.  The loading induces endothermic disordering in shear-transformation zones in the MGs: it’s a powerful energy-pumping mechanism.

The paper builds on earlier work by Miguel Costa (for which he won an Acta 2022 Student Award; Paper of the Month February 2023).  It establishes a new quantification of anelastic effects in materials:  thermal, not just mechanical!

Figure:  The thermodynamics of energy storage in metallic glasses when loaded in the nominally elastic regime.  The energy is stored in shear transformation zones within an elastically deformed matrix.