Neutron-Irradiated mechanical properties of wire arc additively manufactured grade 91 steel

Wire arc additive manufacturing (WAAM) can result in material anisotropy because of the directionality of the additive process, but currently, little is known about the impact of additive-induced anisotropy on radiation-induced material degradation. To investigate the radiation effects as a function of the manufacturing process and to build directionality, three specimens of a WAAM-produced Grade 91 steel in three conditions (two as-printed samples in orientations both parallel [Z-direction] and perpendicular [X-direction] to the build direction, and one heat-treated sample oriented in the X-direction) were subjected to tensile testing before and after neutron irradiation in the High Flux Isotope Reactor to 0.75 and 2.1 displacements per atom (dpa) at a target temperature of 300°C. Tensile tests showed that the orientation of the as-printed specimens greatly affected the strain hardening capacity and elongation after necking before irradiation, and this anisotropy remained after irradiation. Regardless of orientation, the as-printed specimens had greater unirradiated yield strengths and, surprisingly, underwent greater irradiation hardening than the heat-treated specimen. The as-printed specimens initially had unirradiated yield strengths of ∼950 MPa and were further hardened by ∼400 MPa at 2.1 dpa, whereas the heat-treated specimen initially had an unirradiated yield strength of ∼730 MPa and was further hardened by ∼220 MPa at 2.1 dpa. These results underscore the importance of WAAM and post-processing parameters and specimen directionality on the irradiation response of ferritic/martensitic (FM) steels. Notice: This manuscript has been authored by UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the US Department of Energy (DOE). The US government retains and the publisher, by accepting the article for publication, acknowledges that the US government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for US government purposes. DOE will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan .