PNNL

Abstract

Tungsten (W) has been regarded as one of the most promising plasma facing materials (PFMs) in fusion reactors. The formation of bubbles and blisters during hydrogen (H) irradiation will affect the properties of W. The dependence of implantation conditions,such as fluence and energy, is one of the many great interests. In this work, polycrystalline tungsten samples were separated into two groups for study. The thick samples were implanted by 18 keV H3+ ions to fluences of 1E18, 1E19 and 1E20 H+/cm2, respectively. Another thick sample was also implanted by 80 keV H2+ ions to a fluence of 2E17 H+/cm2 for comparison. Moreover, the thin samples were implanted by 18 keV H3+ ions to fluences of 9.38E16, 1.88E17 and 5.63E17 H+/cm2, respectively. Focused ion beam (FIB) combined with scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used for micro-structure analysis, while time-of-flight ion mass spectrometry (ToF-SIMS) was used to characterize the H depth profile. It is indicated that bubbles and blisters could form successively with increasing H+ fluence. H bubbles are formed at a fluence of ~ 5.63E17 H+/cm2, and H blisters are formed at ~ 1E19 H+/cm2 for 18 keV H3+ implantation. On the other hand, 80 keV H2+ ions can create more trapping sites in a shallow projected range, and thus enhancing the blisters formation with a relatively lower fluence of 2E17 H+/cm2. The crack-like microstructures beneath the blisters are also observed and prefer to form on the deep side of the implanted range.