Effect of temperature on hydrogen diffusion mechanism in tungsten: A molecular dynamics simulation study

Abstract

In this research, the diffusion of hydrogen atoms in the crystalline structure of tungsten was investigated using LAMMPS molecular dynamics simulation code. To describe the interatomic interactions of the W–H system, the EAM potential was used. Hydrogen atoms were placed in the tetrahedral sites of a perfect BCC tungsten lattice to simulate a realistic impurity distribution with a concentration of 2 %. Simulations were performed in a temperature range of 1400–2700K. After structure optimization, the Mean Squared Displacement (MSD) was calculated using the Einstein relation to determine the diffusion coefficients for each temperature. The results showed that with increasing temperature, the hydrogen diffusion coefficient increases exponentially and verifies the Arrhenius relationship. The effective activation energy parameter is calculated 1.48 eV, with a pre-exponential factor of 3.2×10⁻⁶m²/s. Physical analysis revealed three distinct diffusion regimes: at low temperatures, hydrogen mobility is limited by trapping effects; at intermediate temperatures, the TIS-TIS pathway is the dominant mechanism; and at high temperatures, the transition to TIS-OIS-TIS pathways is activated, leading to a sharp increase in the diffusion coefficient. The high value of the effective activation energy is attributed to the collective motion and interactions of the hydrogen atoms at this concentration. These results are applicable in predicting the behavior of tungsten under the high-temperature conditions of fusion reactors.