Impact of helium irradiation on the crystallographic orientation change in single-crystalline tungsten *

Understanding the helium effects on the surface modifications of tungsten is of great interest and significance for developing plasma-facing materials. Our recent studies revealed that the ion irradiation of helium at room temperature produces 111-oriented surface grains in single-crystalline tungsten {100} and {110}, which may play an important role in the surface and subsurface evolutions of tungsten subjected to fusion-relevant service environments. Although the driving force for the formation of surface grains is well explained by ion channeling effect, the underlying formation mechanism remains unclear. In this work, we investigated the orientation relationship between irradiation-induced new surface grains and single-crystalline tungsten matrix. The experimental results of electron backscatter diffraction demonstrated that the formation of most 111-oriented surface grains in both helium-irradiated tungsten {100} or {110} can be regarded as the grain rotation of matrix around its in-plane 110 axis.