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

Abstract

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 5wt% rhenium. This damaged layer is only 300nm 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 (0dpa, 0.07dpa, 0.4dpa, 1.2dpa, 13dpa and 33dpa). In pure tungsten the hardness increase is seen to saturate by 0.4dpa at ≈0.8GPa. 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 5wt% rhenium the increase in hardness is constant between 0.07 and 1.2dpa, ≈0.85GPa. The loop volume number density as measured using TEM is also shows little change in this region. At a damage level of 33dpa the hardness increase is 2.88GPa; this corresponds with the formation of small 3–5nm rhenium clusters as observed using atom probe tomography.