Effect of cryogenic milling on the mechanical and corrosion properties of ODS Hastelloy-N

This study entails the fabrication of two oxide-dispersion strengthened (ODS) Hastelloy-N (HN) alloys utilizing divergent methods. The first alloy was synthesized using cryogenic attritor milling coupled with spark plasma sintering (SPS), while the second was produced via room temperature attritor milling and SPS. The ODS HN alloy derived from cryogenic milling demonstrated superior strength relative to its commercial-grade counterpart. Conversely, the alloy produced through room temperature milling exhibited lower ultimate tensile strength (UTS), attributed to manufacturing defects and the precipitation of Zr at grain boundaries. Corrosion resistance in molten FLiNaK for both ODS samples was found to be inferior compared to commercial HN. Particularly, in the room temperature-milled ODS HN, Zr present at grain boundaries appeared to dissolve more readily than in cryogenic or commercial samples, facilitating enhanced penetration by molten salt. The cryogenically-milled ODS HN contained Zr, yet it was not segregated to grain boundaries. Although the homogeneously dispersed Mo-based compound in the cryogenically-milled ODS HN augmented mechanical properties, it also accelerated corrosion propagation beyond that of the commercial-grade alloy.