Flux and fluence dependent helium plasma-materials interaction in hot-rolled and recrystallized tungsten

Tungsten is the primary candidate for plasma-facing materials (PFMs) in a magnetic fusion energy (MFE) devices such as ITER due to its high melting point, excellent erosion resistance, and low sputtering yield. However, tungsten will suffer from heat, neutron irradiation, large flux (1022-1024 He/m2s)- low energy (tens of eV to hundreds of eV) helium and hydrogen ion exposure, as well as microstructure evolution (such as recrystallization). We have exposed hot-rolled and recrystallized tungsten to 65 or 80 eV helium ions with a flux of 0.5 × 1022 or 5 × 1022 He/m2s to total fluence from 0.6 × 1024 to 4 × 1024 He/m2 at a temperature of ≈1100 K. The results show that recrystallized tungsten samples exhibit a roughened surface morphology in certain grains with orientations close to <001>, while hot-rolled tungsten samples still maintain the smooth surface under all helium-ion exposure conditions. All the samples exhibit relatively shallow helium bubble penetration (<100 nm) from cross-section TEM observation. Much deeper helium bubble penetrations were observed in the low flux exposed samples. Under the same flux conditions, the helium bubbles penetrate deeper at higher fluence. The recrystallized samples show deeper bubble distributions compared to hot-rolled samples. While bubble sizes do present distinct distributions between hot-rolled and recrystallized samples with rough or smooth surface, the differences become less pronounced under the higher fluence conditions.