Microstructural characterization of Eurofer-97 and Eurofer-ODS steels before and after multi-beam ion irradiations at JANNUS Saclay facility

Abstract

a b s t r a c t RAFM steels such as Eurofer-97 and Eurofer-ODS are potential structural materials for future fusion reactors. In order to study their resistance to the high energy neutrons they will be subjected to in this context, we have irradiated these materials in single-, dual-and triple-beam mode to 26 dpa at 400 C. In single-beam mode (Fe ions only), both materials resist swelling but dislocation loops form. For dual-(Fe and He ions) and triple-beam (Fe, He and H) modes, the same dislocation loop microstructure is observed as for the single-beam mode, but small cavities form, aided by the presence of gases. Despite the formation of cavities, swelling is very low for the present conditions. The influence of ODS particles on swelling is briefly discussed.

TEM study and modeling of bubble formation in dual-beam He + /Fe 3+ ion irradiated EUROFER97

“…However, in contrast to the dominating nucleation at dislocations and grain boundaries for neutrons at 450 C, we interprete the observed coexistence in the case of ions at 500 C as an early stage of the tendency for heterogeneous nucleation with rising irradiation temperature. Therefore, we indicate a temperature shift larger than 50 C in agreement with reference [22].…”

“…In model alloys dislocation loops caused a spatially heterogeneous distribution of bubbles [34,35] due to a preferential bubble formation at the loops. Nevertheless, the latter was experimentally not observed in the present study even at an elevated irradiation temperature of 500 C as well as in other studies on EUROFER97 [6,22,23].…”

“…A more detailed description of the specimen preparation, the irradiation experiment and the TEM sample preparation can be found in Ref. [22]. The preparation of TEM-samples out of the uppermost irradiated 1 mm thick layer with asymmetric electrolytic-polishing and FIB machining may fail due to thinning at the wrong depth and the additional ion irradiation, respectively.…”

“…With respect to the application of rate-model we limit the present TEM study to the size and density of helium bubbles. For characteristics of dislocations necessary for modeling we will refer on existing studies on EUROFER97 for dual-beam irradiation [22] and neutron irradiation [5,23,24].…”

Evolution of microstructure in advanced ferritic-martensitic steels under irradiation: the origin of low temperature radiation embrittlement

“…It was APT study that revealed considerable changes in nanoclusters in the neutron irradiated steel to 32 dpa at 330 °C. In ODS Eurofer irradiated with heavy ions at low temperatures (RT, 300 °C and 400 °C), dislocation loops were observed [23,29]. TEM study also showed an increase in density of small (< 5 nm) oxide particles [23].…”