Nature of atomic trajectories and convective flow during plastic deformation of amorphous Cu50Zr50 alloy at room temperature-classical molecular dynamics studies

To identify the atomistic mechanism of plastic deformation in metallic glasses (MGs), classical molecular dynamics (MD) simulation of plastic deformation of amorphous Cu₅₀Zr₅₀ alloy is carried out for the strain rates varying from 10^?3 s^?1 to 10¹¹ s^?1 and for two states of stress viz. pure shear and uniaxial tension. Although MD studies of plastic deformation in MGs have been widely reported previously, atomic movements have seldom been studied. In the present study, random movement of atoms, as observed in diffusion, is observed irrespective of the strain rate and state of stress. The average ratio of distance traveled to the magnitude of net displacement by an atom, within a time interval, is found to increase with strain rate. It suggests that the randomness in the atomic trajectories, although present, decreases with the strain rate. At high strain rates, control masses are observed to translate (convective flow) and exchange atoms with their neighboring control masses, losing their individuality within a short time. These observations clearly suggest that there is no such thing as shear transformation zone (STZ), and the atomistic mechanism of plastic deformation in MGs is exactly like that in liquid.