Reactive atmosphere fabrication of nanostructured alumina-forming austenitic alloys for nuclear applications

Abstract

Although advanced austenitic alloys are advantageous in non-nuclear applications due to their high creep strength, designing irradiation-resistant austenitic alloys is challenging due to the difficulty of dispersing irradiation defect-capturing sinks uniformly throughout the material. In this work, nanostructured alumina-forming austenitic (NAFA) alloys were successfully produced with fine multi-precipitate dispersions of oxides and carbonitrides using a reactive atmosphere melting and solidification technique. Following processing, chemical composition analysis confirmed the successful uptake of oxygen within the ball-milled (BM) variant and N2 within the reactive atmosphere build; other compositions remained unchanged based on the processing methodology. It was found that due to the extended high temperature hold times associated with consolidation, that the hot isostatically pressed (HIP) and BM variants exhibited low fracture toughness and lower strength at high temperature due to the nucleation of grain boundary intermetallic phases. Conversely, the LPBF-produced Ar and N2 prints exhibited high tensile strength (900 MPa) and ductility (10%-30%) at 600 °C and fracture toughness values of approximately 100 MPa⋅m1/2. Printing in a nitrogen reactive atmosphere produces Y-rich oxides (10–20 nm diameter) and Zr/Nb-rich carbonitrides (20–30 nm diameter). These spatially anticorrelated precipitate distributions demonstrate the feasibility of multi-dispersion reactive element alloys that can be optimized for strength and irradiation resistance.