tailieunhanh - Báo cáo "Simulation study of microscopic bubbles in amorphous alloy $Co_{81.5}B_{18.5}$"

Simulation of the diffusion mechanism via microscopic bubbles in amorphous materials is carried out using the statistical relaxation models $Co_{}B_{}$ 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 $Co_{}B_{}$ vary from $\times 10^{-3}$ 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. | VNU Journal of Science Mathematics - Physics 26 2010 29-35 Simulation study of microscopic bubbles in amorphous alloy Pham Huu Kien1 Pham Khac Hung1 Vu Van Hung2 Department of Computational Physics Hanoi University of Technology 2 Department of Physics Hanoi National University of Education 136 Xuan Thuy Cau Giay Hanoi Vietnam Received 8 September 2009 Abstract. Simulation of the diffusion mechanism via microscopic bubbles in amorphous materials is carried out using the statistical relaxation models containing 2 X 105 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 vary from X 10 3 to 4 X 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. Keywords Keyworks Bubbles Amorphous alloys Vacancy bubbles Diffusion mechanism Statistical relaxation. 1. Introduction The diffusion behavior in amorphous materials have been investigated by both experiment and computer simulation for a long time 1-23 . For amorphous alloys AMAs the diffusion coefficient of tracer atoms in well-relaxed specimens decreases compared to that in as-quenched ones 1-11 . Generally the diffusivity in AMAs is interpreted as the quasi-vacancies in super-saturation is reduced during thermal annealing until the relaxation is over and the diffusion coefficient reaches