A microscopic study of the glass transition: Atomistic simulations of vitrification and amorphization in metallic systems.

摘要

At present, little is known concerning the details of the transition to the amorphous solid. Several theories on vitrification and amorphization have been proposed, but to date no microscopic model has been developed. We present a molecular dynamics simulation study on vitrification and amorphization in one- and two-component metal systems. We found that the onset of orientational correlations in the shear stresses at a temperature T{dollar}sb{lcub}rm s{rcub}{dollar} are associated with the change from Arrhenian to non-Arrhenian behavior of the transport properties. These correlations lead to four-mode coupling terms which are not presently included in standard mode-coupling theories. Also, these correlations in the shear stress indicate the presence of long-range shear elastic interactions. We also found that the average atomic shear stress and its distribution determines the completion of amorphization when it saturates at a critical value which can be determined from the average shear stress in a quenched glass. This value, in contrast to the thermodynamic values of volume and energy, is not dependent on processing history and is, therefore, a good criterion for amorphization. Also, the average shear stress may be a reasonable description of the glassy state. The average shear stress in an amorphous solid may be measurable experimentally through the use of a local probe like NMR.