Hardening of self ion implanted tungsten and tungsten 5-wt% rhenium

Tungsten is one of the most promising materials for high temperature components in any future nuclear fusion tokamak. In this study tungsten-ion implantation has been used to simulate the damage caused by neutrons in pure tungsten and tungsten 5 wt% rhenium. This damaged layer is only 300 nm deep so conventional mechanical tests cannot be used to investigate it. Nanoindentation has been used to measure the change in hardness as a function of six damage levels (0 dpa, 0.07 dpa, 0.4 dpa, 1.2 dpa, 13 dpa and 33 dpa). In pure tungsten the hardness increase is seen to saturate by 0.4 dpa at ≈0.8 GPa. Transmission electron microscopy of the damage structure sees a similar saturation of the loop volume number density at the same damage level. In the tungsten 5 wt% rhenium the increase in hardness is constant between 0.07 and 1.2 dpa, ≈0.85 GPa. The loop volume number density as measured using TEM is also shows little change in this region. At a damage level of 33 dpa the hardness increase is 2.88 GPa; this corresponds with the formation of small 3–5 nm rhenium clusters as observed using atom probe tomography.