Abstract
Structural relaxation process in the Zr-Cu metallic glasses is investigated by using molecular dynamics simulations. The enthalpy change in isothermal annealing of the glassy state cannot be fitted by a simple exponential function but obeys a stretched exponential function, which indicates that the relaxation in glassy phase is not a single Debye type process. A close examination of individual atomic motion reveals that the enthalpy relaxation is related to a string-like cooperative motion of atoms. The analysis of the local symmetry around each atom shows that a network of the icosahedral clusters grows in the glassy phases during annealing and it closely relates to the free-volume annihilation in the structural relaxation.
Highlights
Glass transition always has a kinetic nature
Molecular dynamics (MD) simulation is a powerful tool to understand the atomistic mechanism of dynamical processes such as the structural relaxation
In the present study, structural relaxation processes in glassy phases of the Zr-Cu binary system are investigated by using molecular dynamics (MD) simulations
Summary
Glass transition always has a kinetic nature. Structure and all physical properties such as enthalpy, entropy and volume are frozen in due to extreme slowdown of atomic mobility at the glass transition point. The structural relaxation is accompanied by free-volume annihilation in the glassy state. The atomistic mechanism that causes the free-volume annihilation is not understood at all, because such microscopic behavior is difficult to investigate by experimental methods. Molecular dynamics (MD) simulation is a powerful tool to understand the atomistic mechanism of dynamical processes such as the structural relaxation. In the present study, structural relaxation processes in glassy phases of the Zr-Cu binary system are investigated by using MD simulations. We pay special attention on the enthalpy change and the free-volume reduction in isothermal annealing, the atomic motions during the relaxation process, and the change of local icosahedral symmetry in the annealed glass
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