In this work, we have studied the effect of helium and its injection mode on the microstructure of Type 316 and titanium-modified Type 316 stainless steels, both in their solution-annealed and cold-worked states. Irradiations have been conducted in a dual-beam accelerator to doses up to 150 dpa in a wide range of temperatures, from 550 to 750°C. Different injection modes have been investigated: cold preinjection, hot preinjection, and dual beam.
The results show that the effect of helium on swelling is largely dependent on the injection mode and also on the chemical composition of the alloy considered. In Type 316 steel, the presence of helium decreases swelling, the major effect being observed when helium is preinjected at room temperature. In titanium-modified steels, if a high density of tiny helium bubbles are present in all the specimens containing helium, void swelling only occurs for dual-beam irradiations.
In conclusions, this work shows that the effect of helium on void swelling depends on its injection mode, but also that the sense of this effect is clearly different when comparing the behavior of a low and a high swelling alloy.