Influence of heavy ions pre-damage on the blistering and helium bubble in tungsten under helium ions irradiation

Surface blistering and helium bubble in tungsten pre -damaged by 640 keV argon (Ar) ions to a fluence of 9.16 x 1018 ions/m2 followed by 40 keV helium (He) ion irradiation with a fluence of 6.2 x 1021 ions/m2 were investigated. It is shown that the nano -hardness of the sample was significantly improved after Ar ions implantation. In addition, the preferred orientation of the grains was also changed after Ar ions implantation. After He ions irradiation, a great many of the blisters with a diameter of 1 mu m were formed on the surface of W without any pre -irradiation. However, many large blisters with a diameter of 3 mu m were formed for the damaged W, indicating that Ar ions irradiation significantly enhanced the blistering. The blister cap was cut using focused ion beam technology, and it can be found that the damaged tungsten blister cap is thicker than the undamaged tungsten blister cap. Transmission electron microscopy (TEM) results revealed that dense He bubbles with a size of approximately 2 nm were observed in the undamaged W after He ions irradiation. For Ar ions damaged W, the size of He bubbles was approximately 2 times as large as that in the referenced W, suggesting that Ar ions preirradiation can promote the growth of He bubbles.