Self-Diffusion Parameters of Grain Boundaries and Triple Junctions in Nanocrystalline Materials

Abstract

Suggested methods describe the process of self-diffusion along grain boundaries and triple junctions in polycrystals without using geometric models of the grain boundaries structure. The calculation method introduced diffusion characteristics along grain boundaries derived from the results of molecular dynamic simulations of nanocrystalline materials. The diffusion experiments were imposed to establish relationship between introduced diffusion characteristics and the diffusion parameters along grain boundaries and triple junctions of the Fisher’s grain boundary diffusion model. By the example of copper for the first time the characteristics of self-diffusion along grain boundaries of nanocrystalline materials and coarse grained analog defined in the same temperature range was compared for the first time. It was found that values of the self-diffusion characteristics along grain boundaries in high purity nanocrystalline and polycrystalline copper are equal at the same temperatures.

The Causes of Formation of the Triple Junctions of Grain Boundaries Containing Excess Free Volume in fcc Metals at Crystallization

“…According to numerous experimental data, the diffusion along the triple junction proceeds more intensively than along the grain boundaries [1,2], and the triple junction is often characterized by relatively "loose" structure (even with inclusion of the amorphous phase [3]) with a higher content of free volume compared with the grain boundaries forming the junction. However, in the comparatively recent studies [4,5] performed using the computer simulation, the conclusion is made that the diffusion permeabilities of the grain boundaries and the triple junctions can have the same order of magnitude. We obtained the analogous result in [6], moreover, it is shown that formation energy of the triple junction as a special defect is practically zero, and the triple junction is, in fact, part of its constituent grain boundaries.…”

Necessary Duration of Molecular Dynamics Simulation for Calculation of Self-Diffusion Coefficient during Migration of Different Point Defects in Nickel

“…Typically, the computer experiment duration to calculate the diffusion coefficient is several hundred picoseconds (when the duration of one iteration is 1-10 fs) [3][4][5][6][7][8][9]. However, special studies on this topic are rare, especially, for different types of migrating defects.…”