On the nature of low temperature internal friction peaks in metallic glasses

Low temperature (30 <T <300 K) internal friction in a metallic glass Ni60Nb40 subjected to preliminary inhomogeneous deformation by cold rolling, homogeneous tensile deformation or electrolytic charging with hydrogen is investigated. Cold rolling or hydrogenation result in appearance of similar internal friction peaks and hysteresis damping. Homogeneous deformation has no influence on low temperature internal friction. The phenomenon of microplastic deformation during hydrogenation of weakly stressed samples is revealed. It is argued that microplastic deformation of metallic glasses during hydrogenation without external stress takes place too. Plastic how both on cold rolling and hydrogenation occurs via formation and motion of dislocation-like defects which are the reason of the observed anelastic anomalies. It is concluded that low temperature internal friction peaks described in the literature for ''as-cast'', cold deformed and hydrogenated samples have common dislocation-like origin

Non-isothermal strain recovery as a result of irreversible structural relaxation of metallic glasses

A quantitative model is proposed for the non-isothermal strain recovery induced by stress pre-annealing of metallic glasses. It is assumed that the nonisothermal strain recovery is determined by irreversible atomic rearrangements occurring in directional internal stress fields created by unloading of samples preannealed under stress. Special experiments are performed to make a thorough test of the model. It is shown that the model correctly reproduces the temperature position and height of the recovery strain rate peak observed in the experiment. It is concluded that the macroscopically reversible mechanical behaviour (strain recovery) can be determined by irreversible structural relaxation of a metallic glass