Ultrasonic vibration accelerated aging in La-based bulk metallic glasses

The effect of ultrasonic vibrations on the thermodynamic properties of La-68.5 Al14Ni16Co1.5 bulk metallic glasses is systematically studied at various temperatures. We find a significant enthalpy lowering for the glasses after the ultrasonic treatment, due to the structural relaxation towards lower energetic states, coinciding with the finding that the pretreated samples have a noticeable higher energetic barrier for glass transition. With increasing the ultrasound-treating time, the reduced enthalpy saturates in the long-time regime, which is reachable by the isothermal annealing. Based on these results, we conclude that the ultrasonic vibration has, qualitatively, the same effect as that of the annealing process. This is interpreted by the fact that the ultrasonic perturbation is weak for the technique we utilized, and most of the atoms could linearly respond to it. The ultrasound-accelerated aging has also been shown on the aspect of the hardness that was monotonically enhanced with the treating time.