Anomalous decrease of propagation rate of the macroscopic shear band in the Zr-based bulk metallic glasses at temperatures 170 and 77 K

The plastic deformation and fracture of cylindrical samples of the bulk metallic glasses Zr₆₂Cu_15.5Ni_12.5Al₁₀ and Zr_64.13Cu_15.75Ni_10.12Al₁₀ have been studied in uniaxial compression in the temperature range 300-4.2 K. At the temperature 300 K the deformation curve has serrated (jump-like) type, caused by the propagation of narrow shear bands. At the deformation level of approximately 3-4% the catastrophic, uncontrolled failure of the specimens occurs resulting from propagation of the macroscopic shear band with a rate ∼10³ m/s, which is comparable with the sound velocity. A decrease of the temperature from 300 K down to 170 and 77 K changes the type of deformation curves from a jump-like to a smooth one. An interesting low temperature anomaly of deformation process was found: "slow" (with a rate of approximately 10^-6 m/s) propagation of a single macroscopic shear band is observed at 170 and 77 K. When the samples are cooled to 4.2 K their macroscopic plasticity vanishes, and they undergo fracture, just as at 300 K, as a result of the propagation of the catastrophic shear band with nearly sound speed.