Loading rate sensitivity of nanoindentation creep behavior in a Fe-based bulk metallic glass

Effect of loading rate on room temperature creep deformation of {[(Fe0.6Co0.4)0.75B0.2Si0.05]0.96Nb0.04}96Cr4 bulk metallic glass (BMG) was investigated by performing nanoindentation creep experiments. Experimental results show that the creep displacement of the Fe-based BMG increases with increasing the loading rate. Furthermore, based on an empirical power-law equation, the stress exponent for room temperature creep of this BMG was calculated. As the indentation loading rate increases from 1 mN/s to 50 mN/s, the stress exponent decreases gradually from 28.1 down to 4.9, exhibiting significant indentation loading rate sensitivity. Finally, nanoindentation creep behavior in this Fe-based BMG was demonstrated in terms of free volume and “shear transformation zone” (STZ) theories, which could provide semi-quantitative explanation as for the observed experimental and analytical results.