Wire and arc additive manufacturing fabrication of ODS-RAFM steels and preliminary evaluation on microstructures and mechanical properties

Abstract

Oxide-dispersion-strengthened reduced-activation ferritic/martensitic (ODS-RAFM) steels have promising applications in future fusion reactors, but the rapid and cost-efficient fabrication of ODS-RAFM steel components still remains a major challenge. In this study, wire and arc additive manufacturing (WAAM) techniques were developed to fabricate a thin-wall ODS-9Cr-RAFM steel part, using flux cored wires containing nano-Y2O3 as the [Y] and [O] sources and Ti as micro-alloying element. Their microstructures and mechanical properties before and after austenite-quenching were both investigated, and the results were compared with other 9Cr-RAFM counterparts without the addition of nano-Y2O3 and Ti. It was suggested that Y2O3 could decompose into [Y] and [O] during the rapid melting, and then precipitate along with Ti as Y2TiO5 mostly (and perhaps also TiO2) during the rapid solidification of WAAM. These oxides have fine nano-sizes with a high number density and can provide multi-fold benefits from refining the grain/sub-grain structures, promoting martensite transformation, to pinning dislocations. After the aus-quenching, a new, more stable nano-phase of Y2Ti2O7 was formed, with combined features of ultra-fine size, high number density, and high coherency. The as-quenched ODS-9Cr-RAFM specimens can achieve markedly high strengths with good plasticity, both at room temperature and elevated temperatures up to 650 °C, showing great promises of WAAM techniques for large-scale fabricating high-performance ODS-RAFM steel structural components.