Effects of testing conditions on the deformation behaviour of a Ti-based bulk metallic glass

This study investigated the deformation behaviour of a Ti32.8Zr30.2Ni5.3Cu9Be22.7 bulk metallic glass via indentation and compression tests with loading rate ranging from 30 μN/s to 30000 μN/s. The load-displacement (P-h) curves show evident displacement bursts (pop-in events). The statistic analysis reveals that the pop-in events are correlated to the loading rate, i.e., the pop-in size increasing linearly with the indentation depth and decreasing exponentially with the loading rate. Cube corner indenter with much sharper geometry favours the promoting of pronounced pop-in events, compared to Berkovich indenter. Similar loading rate effect can be observed in the micro-pillar compression tests. SEM observation of the deformed pillars reveals that the shear bands (along a ~50.7° plane with respect to the loading axis) initiate from the side wall and run across the entire pillars. The free-volume theory and shear transformation zone (STZ) are used to explain these observations quantitatively. The serration to smooth shape of P-h curves is most likely due to the simultaneous operation of multiple shear bands at high loading rate while the single shear band contribution could not be resolved.