Simulation study of microscopic bubbles in amorphous alloy $Co_{81.5}B_{18.5}$

Abstract

Simulation of the diffusion mechanism via microscopic bubbles in amorphous materials is carried out using the statistical relaxation models $Co_{81.5}B_{18.5}$ containing $2\times 10^5$ atoms. The present work is focused on the role of these bubbles for self-diffusion in amorphous solids. It was found that the numbers of the vacancy bubbles in amorphous $Co_{81.5}B_{18.5}$ vary from $1.4\times 10^{-3}$ to $4\times 10^{-3}$ per atom depending on the relaxation degree. The simulation shows the collective character of the atomic movement upon diffusion atoms moving. Due to the large size in comparison with B atom, the jump of a Co diffuses atom leads to a significant local rearrangement of the atoms located near the VB. Meanwhile, B diffuses like the movement of an interstitial impurity through the boron-VB. Diffusion coefficients have been calculated via the vacancy bubbles and they are consistent with experimental data. The effect of the relaxation is also investigated and interpreted as a result of vacancy-bubble annihilation during thermal annealing.