Molecular Dynamics Simulation of Helium Atom Diffusion in Iron-Chromium Bicrystal Grain

摘要

Helium has very low solubility in metals leading to formation of helium clusters and complexes with vacancies/interstitials. Clusters and complexes then diffuse and coalesce to form helium bubbles of nanometric size or higher. These bubbles are one of the reasons for the brittle failure of materials. In order to study the diffusion process, molecular dynamics simulations of helium diffusion in FeCr grain boundaries are carried out for different orientations of the bicrystal. A total of eight different configurations of the bicrystal, have been studied in the temperature range of 700-1,000 K. Potential energy analysis of host and grain boundary (GB) atoms predicts average GB potential energy in the range of 3.7 to 3.6 eV, which is 0.2 eV higher than that in the host matrix. The migration energy of helium in grain boundary is found to be 0.3-0.7 eV, which is an order of magnitude larger than that in the bulk crystal. The grain boundary width calculated for all the bi-crystals lie within 11-14 and the cage distance of helium atom is of the order of the bond length (2.87 ) of the host atoms. For orientation more than 100 helium trajectories have been analysed to measure the statistical variation of migration energy.