Fluence dependence of helium ion irradiation effects on the microstructure and mechanical properties of tungsten

To understand the effect of helium ion irradiation on the microstructure and mechanical properties of tungsten (W), recrystallized W is irradiated by 80 keV helium ions with fluence of 3 × 1015, 3 × 1016 and 3 × 1017 ions/cm2. Transmission electron microscope (TEM) observation suggests that large numbers of dislocation loops are generated in W and the size of the dislocation loop increases with irradiation fluence. The results of micro-hardness and nanoindentation show that the irradiation hardening can be clearly detected after helium ion bombardment with displacements per atom (dpa) of <1 dpa. However, this hardening effect becomes milder when the irradiation fluence is further increased. Finally, the irradiation hardening behavior of W is analyzed by the dispersed barrier model and the calculated results follow the same trend with that of nanoindentation.