The influence of silicon and helium on the microstructural stability of ion-irradiated Incoloy DS alloys

In order to test their void swelling behaviour under irradiation, several alloys based on the solid-solution nickel alloy Incoloy DS (18Cr-38Ni-Fe) with additions of 0.05, 0.43, 0.92 and 2.24 wt% Si have been studied using 4 MeV helium and 46 MeV nickel ion irradiation in the Harwell VEC. For irradiations of 60 dpa with 10 appm He the void swelling decreased from ≅ 0.9% to negligible levels with increasing silicon content. After irradiation to 90 dpa following injection with 10 appm He the 2.24% Si alloy showed < 1.0% swelling at an apparent peak swelling temperature of 6250C. This alloy was subsequently irradiated to check the swelling response with concentrations of helium and hydrogen appropriate to fusion-reactor conditions. Following irradiation to 60 dpa after 1000 appm He injection the swelling peak was shifted to 5750C where a swelling maximum of 4% was observed. At 6250C with 1000 appm He alone, swelling was 2.0% compared with 1.2% in samples injected with 1000 appm He + 1000 appm H. This small reduction in swelling was associated with a higher cavity (bubble) concentration in the hydrogen implanted sample. Fine-scale precipitation of Ni3Si(γ'), η-carbide and G-phase was observed after irradiation together with helium bubbles attached to the η- and G-phase precipitates. The precipitation and void swelling was significantly greater in irradiated samples containing 1000 appm He than in those with 10 appm and irradiated to 90 dpa. (orig./MM)