Hydrogen diffusion and vacancy clusterization in iron

Molecular statics and molecular dynamics simulations were performed to study hydrogen diffusion and vacancy clustering in alpha iron. In particular, it was found that hydrogen atom binds very strongly with vacancies, rather than other hydrogen atoms. The monovacancies were inclined to form the VH4, VH3, VH2 and VH1 complexes, rather than VH6 in the range of our simulated temperatures. The rate of hydrogen diffusion was apparently reduced in the presence of vacancies, while the vacancy trap effect was gradually weakened with increasing temperature. The presence of vacancies changes the diffusion mechanism of H atoms. Moreover, we found that vacancy clusters tended to be formed at the moderate range of temperatures, and fewer clusters were observed at either low or high temperatures. The number of vacancy clusters reduced, while hydrogen-vacancy clusters were gradually created with the increase of hydrogen concentration.