Ion Irradiation Effects on a Martensitic Stainless Steel Designed for Reduced Long-Life Radioactivity

Alloys with reduced long-life radioactivity (low-activation alloys) are being developed to increase the acceptability of fusion power. The phase stability and swelling resistance of a 12Cr-6.5Mn-lW-0.3V-0.1C martensitic steel were evaluated by transmission electron microscopy following 3.8-MeV Fe⁺⁺ ion irradiation with and without He+ coimplantation. Ion irradiations were performed at 450, 550, and 650°C to approximately 10,20, and 40 dpa. At 550°C, approximately 20 appm He/dpa was coimplanted with the 3.8-MeV Fe⁺⁺ ions. The specimens were examined at a depth approximately halfway between the surface and the mean ion range in order to minimize the influence of both the surface and of injected ions.

At all temperatures, M23C6, also present in the unirradiated structure, was the only precipitate found to be present. A nonuniform distribution of loops also formed at all temperatures. After the 450 and 650°C irradiations, no voids were found. At 550°C, the helium did not appear to have much effect. Very few faceted voids formed. At 20 and 40 dpa some bubbles were found, but their density was very low. At 650°C, a structure similar to a heavily over-tempered steel was produced by the irradiation. At 550°C, recovery was seen to a lesser extent. Little recovery was seen at 450°C.