Influence of helium-decoration on the interaction between 1/2 dislocation loop and edge dislocation in BCC iron

Abstract

For ferritic steels served as structural materials for future nuclear reactors, a large number of helium atoms are expected to be introduced through transmutation reaction. Current experimental results prove that these helium atoms tend to segregate at different crystal defects and deteriorate the mechanical properties of materials severely. In this work, the helium segregation on 1/2[11‾1] dislocation loops (DLs) in body-centered cubic iron and the concomitant hardening effects were investigated by a combination of Monte Carlo and molecular dynamics methods. The Monte Carlo results reveal that the helium atoms are inclined to segregate as helium bubbles at six energetic favorable sites which divide the DLs periphery uniformly, irrespective of the shapes of DLs. The Molecular dynamics simulations were then performed to study the interaction between a moving edge dislocation and the helium-decorated DLs. In order to investigate the helium-decoration effects systematically, influence factors including the DLs size, helium content, and the relative geometric position between edge dislocations and DLs were considered. It is shown that the decoration of helium bubbles suppresses the absorption of DLs by the moving edge dislocation through hindering the movement of dislocation segments during the interaction. Four types of residual products induced by the edge dislocation-DLs interaction are observed, while three of them, including a pure <100> DL and two kinds of bi-DLs, had never been reported before. It is also found that helium-segregation overall increases the critical shear stress for the edge dislocation bypassing DLs. These results may be helpful for a deeper atomic-scale comprehension of the helium-induced hardening and embrittlement in ferritic steels.