He ion implantation induced He bubbles and hardness in tungsten

The pure tungsten was implanted with 500 keV helium (He) ions to a fluence of 1.0 × 1017 ions/cm2 at RT and 800 °C. After the implantation, cross-sectional transmission electron microscope (TEM) and nano-indentation measurements were used to investigate the He bubbles and hardness profiles induced by He implantation. Visible He bubbles were observed only in the damage peak region at RT but in the whole damage region at 800 °C. The size of He bubbles at 800 °C increased with increasing depths. With increasing the implantation temperature from RT to 800 °C, the size of He bubbles in the damage peak regions increased. The nano-indentation tests indicated that hardening was induced by He implantation at RT and 800 °C. The implantation induced peak hardness values were the same at both temperatures, but the hardness peaks moved to the surface with increasing temperatures. The formation of He bubbles and the contributions of their distribution and sizes to the hardness were discussed.