Atomistic investigation on grain boundary effect on helium segregation and clustering in iron

Molecular dynamics simulation was applied to study the behavior of helium segregation and clustering near different grain boundaries (GBs) in α-Fe. The 〈110〉 and 〈100〉 family symmetric tilt grain boundaries (STGBs) covering a wide range of GB energy and misorientation angle were investigated. The present results indicate that the major factor of GB characteristic effects on helium behavior at the grain boundary are the GB energy and structure. Generally, the proportion of helium that is bound to the grain boundary is higher for high-energy grain boundaries than for low-energy grain boundaries. However, the three grain boundaries with the highest energy lose their original structure units and become disordered under the combined effects of high temperature and helium bubble-induced stress field, forming a diffusion “barrier” for He interstitials to enter the GB plane, thus lead to the slight decrease of the proportion of segregated helium. Four typical He migration patterns at different grain boundaries are found, which depends on the GB structure and energy. In general, with the increase of GB energy, the average diameter of He-V clusters at the GB becomes smaller, and the cluster density becomes larger.