Preliminary study on the microstructure and hardness of wire and arc additively manufactured ODS-RAFM steel subjected to 2.5 MeV Fe ion irradiation

Abstract

This work aims at exploring the irradiation resistance of oxide-dispersion-strengthened reduced-activation ferritic/martensitic (ODS-RAFM) steel prepared by a rapid and cost-efficient method, wire and arc additive manufacturing (WAAM). WAAM ODS-RAFM steel and RAFM steel were prepared using flux cored wires with and without addition of Y2O3, respectively. Both specimens were irradiated with 2.5 MeV Fe ions at 450 °C to a fluence of 1.84 × 1016 ions cm−2, corresponding to a peak damage dose of 20 dpa. The microstructure, hardness and defect structure of WAAM ODS-RAFM steel before and after irradiation were investigated and compared with RAFM steel. It is found that nano-Y2Ti2O7 particles with a high number density (∼10 nm, 1022/m3) are formed in WAAM ODS-RAFM steel, which pin grain boundary and dislocations motion, thus rendering a stable matrix structure after irradiation. The particle size of the stable nano-Y2Ti2O7 slightly increases to ∼ 15 nm while its number density is still high (1022/m3) after irradiation. The grain boundaries, dislocations and nano-Y2Ti2O7 interfaces act as defect sinks to absorb irradiation-induced defects such as self-interstitial atoms and vacancies. Therefore, small dislocation loops (3.6 nm) are found to be the main irradiation defects while no voids are observed. As a result of the inhibited formation and growth of defects, the irradiation hardening is insignificant (ΔH0 = 0.16 GPa), showing great promises of WAAM ODS-RAFM steel as structural components in future fusion reactors.

Keywords

• Wire and arc additive manufacturing
• Oxide dispersion-strengthening
• RAFM steel
• Irradiation damage
• Nanoindentation