Effects of deuterium plasma exposure and helium ions irradiation on nanoindentation hardness of tungsten

Irradiation hardening is one of the service performance concerns for tungsten in fusion reactors. This work investigated the effect of deuterium (D) plasma exposure and helium (He) ions irradiation on the hardening behavior of the same tungsten sample using nanoindentation. The results demonstrate that the hardness of tungsten increases after D plasma exposure, He ions irradiation, and synergistic irradiation of He-ion and D-plasma. In general, the degree of hardening is He-ion + D-plasma irradiation, individual He-ion irradiation, and D plasma exposure in descending order. D plasma exposure results in an increase in hardness of more than 10 %, which is attributed to the pinning of dislocations by D plasma-induced defects and D-defect complexes (clusters). In the case of the He-ion irradiated tungsten, a large number of defects such as He nanobubbles induced by He-irradiation result in a 70 % increase in hardness. The superposition effect on the hardening of tungsten by D plasma exposure after He ions irradiation was observed, which essentially remains an increase in hardness due to D plasma exposure. This implies that the degradation of mechanical properties caused by D plasma exposure on tungsten will not be overlapped by other particle irradiation. Moreover, He bubbles in tungsten remain stable and grow slightly after annealing at 1173 K, resulting in a limited decrease in hardness.