Hydrogen atom solution and diffusion behaviors at Σ3 and Σ5 grain boundaries of Fe, Ni, Cu and Al: A first-principles study

Abstract

Understanding the interactions between hydrogen atom and grain boundaries is essential for designing grain boundary structures that can improve the hydrogen embrittlement resistance. In this study, the DFT calculations have been performed to investigate the characteristics of Σ3 and Σ5 grain boundaries of Fe, Ni, Cu and Al and the hydrogen atom solution and diffusion behaviors at these grain boundaries. The calculation results indicate that for the same metallic material, the Σ5 grain boundary has larger grain boundary energy and lower work of separation than that of Σ3 grain boundary. The hydrogen atom solution energies at Σ5 grain boundaries are lower than those at Σ3 grain boundaries. The COHP calculations illustrate that the existence of hydrogen atom will weaken the metallic bond strength at grain boundary no matter in Σ3 or Σ5 grain boundary. With respect to the hydrogen atom diffusion behaviors at the grain boundaries, the hydrogen atom is easier to diffuse at the Σ5 grain boundary compared to that of Σ3 grain boundary for the same metallic material. Thus, increasing the ratio of grain boundaries with lower value of Σ will beneficial to improve the hydrogen embrittlement resistance of metallic polycrystalline materials.