Structural defect accumulation in tungsten and tungsten-5wt.% tantalum under incremental proton damage

We have performed proton irradiation of W and W-5wt.%Ta materials at 350 °C with a step-wise damage level increase up to 0.7 dpa and using two beam energies, namely 40 keV and 3 MeV, in order to probe the accumulation of radiation-induced lattice damage in these materials. Interstitial-type a/2 <111> dislocation loops form under irradiation, and their size increases in W-5Ta up to a loop width of 21(4) nm at 0.3 dpa, where loop saturation takes place. In contrast, the loop length in W increases progressively up to 183(50) nm at 0.7 dpa, whereas the loop width remains relatively constant at 29(7) nm and ≥0.3 dpa, giving rise to dislocation strings. The dislocation loops and networks observed in both materials at later stages act as effective hydrogen trapping sites, so as to generate hydrogen bubbles and surface blisters. Ta doping delays the evolution of radiation-induced dislocation structures in W, and consequently the appearance of hydrogen blisters.