Structural Suppression of Blister Formation on the Surface of Tungsten under 30-keV He+-Ion Implantation

The effect of ultrafine-grained structure and cone-shaped surface morphology on the formation of blisters under the irradiation of tungsten with He+ ions at an energy of 30 keV is studied. In comparative experiments, ultrafine-grained and fine-grained samples with an average grain size of 300 nm and 7 μm, respectively, with smooth and cone-shaped surface morphology are used. The ultrafine-grained structure in tungsten samples is obtained by severe plastic deformation, and the cone-shaped surface morphology is obtained by high-fluence irradiation with Ar+ ions at an energy of 30 keV. It is found that blisters are formed on both the fine-grained and ultrafine-grained samples when irradiated with He+ ions at a fluence of 1018 ion/cm2. On the fine-grained samples, some of the blisters are without caps, while in the ultrafine-grained samples, all blisters are intact. The thickness of the caps and the diameter of the blisters depend on the grain size. The cone-shaped surface morphology on ultrafine-grained tungsten is found to suppress blister formation.