Characterisation of radiation damage in W and W-based alloys from 2Â MeV self-ion near-bulk implantations

The displacement damage induced in W and W-5 wt.% Re and W-5 wt.% Ta alloys by 2 MeV W+ irradiation to doses 3.3 × 1017-2.5 × 1019 W+/m2 at temperatures ranging from 300 to 750 °C has been characterised by transmission electron microscopy. An automated sizing and counting approach based on Image J (a Java-based image processing programme developed at the National Institutes of Health) [1] has been performed for all near-bulk irradiation data. In all cases the damage comprised dislocation loops, mostly of interstitial type, with Burgers vectors b = 1/2〈1 1 1〉 (>60%) and b = 〈1 0 0〉. The diameters of loops did not exceed 20 nm with most being ⩽6 nm diameter. The loop number density varied between 1022 and 1023 loops/m3. With increasing irradiation temperature, the loop size distributions shifted towards larger sizes, and there was a substantial decrease in loop number densities. The damage microstructure was less sensitive to dose than to temperature. Under the same irradiation conditions, loop number densities in the W-Re and W-Ta alloys were higher than in pure W but loops were smaller. In grains with normals close to z = 〈0 0 1〉, loop strings developed in pure W at temperatures ⩾500 °C and doses ⩾1.2 dpa, but such strings were not observed in the W-Re or W-Ta alloys. However, in other grain orientations complex structures appeared in all materials and dense dislocation networks formed at higher doses.