Dynamic migration of <100> interstitial dislocation loops under pure W and W containing helium impurity (010) surfaces studied by molecular dynamics simulation

In the fusion irradiation environment, dislocation loop defects occur under the plasma-facing tungsten surfaces, which affect its mechanical properties and hydrogen/helium retention. This paper presents a study that dynamic behaviors of a loop with a radius of 1 nm under the W surface are simulated by using molecular dynamics simulation at the atomic level. It finds that the dislocation loop direction, bulk temperature, depth, and helium atoms have great influence on the motion of the dislocation. This study shows that the dislocation loop ( is the Burgers vector, is the surface normal direction) tends to move towards the surface and the dislocation loop tends to stay in the material. In the course of its migration, the habit plane of dislocation loop may change and the internal stress reduces gradually. The probability of a dislocation loops escaping from the surface is over 90% when the temperature is higher than 800 K and their initial depth is less than 5 nm. The dislocation loop can escape from the surface when the temperature is 800 K and the initial depth is less than 2 nm. It is found that dislocation loops decompose into dislocations at elevated temperatures. Helium atoms impedes the migration of dislocation loop and increases its retention time. The existence of dislocation loops results in the uneven distribution of helium atoms under the W surface, and will potentially affect the surface morphology of tungsten.