Molecular dynamics study on the diffusion behavior of Li in the grain boundaries of α-Fe

Highlights: • Confirmed the strong binding effect between the grain boundaries and lithium interstitials. • Determined the critical temperatures for a lithium atom to diffuse in the grain boundaries. • Revealed that the diffusion mechanism of a lithium atom depends on the grain boundary structure. - Abstract: Liquid lithium has been considered as a candidate material for several components of future fusion devices. Since the containment materials are usually ferrous alloys, molecular dynamics simulations were performed to study the diffusion behavior of lithium atoms along <110> tilt grain boundaries (GB) including Σ9{114}, Σ11{113}, Σ3{112} and Σ11{332} in α-Fe. The binding energies of a Li interstitial to the GBs were calculated. The results suggest that all the GBs have strong binding effect on the Li atom. The critical temperatures for the Li atom to diffuse were determined. The diffusion process of a Li interstitial in the GBs was systematically analyzed. It turns out that the diffusion mechanism depends on the GB structures. For Σ11{113} and GB Σ9{114}, the Li atom was trapped by the Frenkel defect around the GBs at 300 K and 400 K respectively and therefore the diffusion was slowed down rapidly. For Σ3{112}, no defects were formed around GB and the Li atom diffused into Fe bulk at 700 K and above. For Σ3{112}, the diffusion process is driven by the movement of the GB. Finally, the diffusion coefficient, as well as the activation energy, was evaluated.