Microstructure and Tensile Properties of Alumina Forming Austenitic Alloys Fabricated by Laser Powder Bed Fusion

Nuclear fast reactors designed for high power production (>450 MW) rely on forced convection of media such as supercritical CO₂, sodium, or liquid Pb, to cool the nuclear core and transfer heat to an exchanger for energy production. Temperatures are expected to be as high as 950 °C, requiring an alloy with good high temperature strength and corrosion resistance for fabrication of the heat exchangers and other critical reactor components. A new class of high strength low-cost Fe-based alloys are being developed called alumina forming austenitic (AFA) steels, which promote the formation of Al₂O₃ for enhanced passivation, and are stable at desired temperatures. This study investigates an optimized AFA composition processed by laser powder bed fusion (LPBF), finding an ideal processing window in which the alloy could be processed to >99.9% dense. The microstructure was investigated using electron microscopy, which revealed a fine sub-grain cellular structure, decorated with carbide and oxide precipitates. The difference in tensile properties at 20-900°C between the LPBF AFA alloy and its cast counterpart can be attributed to the refined LPBF AFA microstructure.