Abstract
We performed a study of the sub-Tg enthalpy relaxation effect in a bulk Zr-based metallic glass by means of calorimetric and shear modulus measurements. It is found that the increase of the heat absorption in the supercooled liquid state due to sub-Tg preannealing can be well described by a kinetic equation derived within the framework of the Interstitialcy theory. This equation assumes that the heat effects are controlled by the relaxation of the shear modulus occurring upon heating. It is revealed that the heat absorbed during temperature rise up to the supercooled liquid region linearly increases with the shear modulus measured near the room temperature. It is argued that this relationship is determined by a change of glass internal energy, which is controlled by the shear moduli of glass and maternal crystal.On the other hand, it is suggested that sub-Tg enthalpy relaxation as well as relaxation of the shear modulus are governed by concentration changes of interstitialcy-type defects inherited from the melt. This approach, in particular, allows explanation of a new dependence of the heat absorbed during sub-Tg enthalpy relaxation experiment as a function of the preannealing time at temperatures well below Tg.Overall, the obtained results give further clear confirmation of a major role of the shear elasticity in relaxation phenomena in metallic glasses.
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