Non-uniform corrosion of UNS N10003 alloy induced by trace SO42- in molten FLiNaK salt

Abstract

An un-expected non-uniform corrosion was observed for the UNS N10003 alloy immersed in static molten FLiNaK salt at 650 °C for 400 h. Results show that corrosion nodules with pores, embedded particles and boundaries inside form at some surface areas of the alloy, whereas other surface areas remain flat. Meanwhile, fine Cr3S4 precipitates form at grain boundaries and carbide-matrix phase boundaries beneath the surface. The non-uniform corrosion is mainly induced by the trace amount of SO42- in the salt, which causes the surface depletion of Cr and Fe, and internal sulfidation of Cr and Mo in the alloy.