Corrosion of an Amorphous Coating System Exposed to Molten FLiNaK Salt Nuclear Reactor Coolant at 750 oC

The requirements for more efficient and cleaner energy generation exposed structural alloys for power generation,
which experience severe degradation due to hostile operating environments. Hence, high-performance
materials are needed to resist corrosion and erosion processes. The next generation of nuclear reactor systems
is expected to operate at high temperatures to achieve high thermal-to-electrical conversion efficiency
and enable cost competitiveness with conventional electrical power generation methods. Armacor X80®, an
amorphous iron-based thermal spray coating alloy tested in a molten salt reactor (MSR) FLiNaK coolant,
seems to be an alternative to Ni-based alloys. MSR cooling systems present several technical and engineering
challenges due to their highly corrosive characteristics to typical materials. Amorphous metals (AM)
are a novel class of materials with a disordered, non-crystalline, glassy structure. Due to their unique microstructure,
AM combines ultrahigh strength, high hardness, and ductility in one single material. AM are
more corrosion resistant than conventional metals due to the lack of long-range periodicity, related grain
boundaries, and crystal defects such as dislocations.
In this presentation, we will discuss the benefits of using amorphous thermal sprayed coatings on UNS N06230
(Haynes 230) and UNS 31600 (316SS) stainless steel. We conducted corrosion testing on both coated and
uncoated Haynes 230 and 316SS alloys when exposed to molten FLiNaK salt at 750 oC. The purpose of the
coating was twofold: to protect the alloys from corrosion, as evidenced by no depletion of Cr, and to create a
barrier protective layer that resulted in minimal Cr depletion and no degradation of the coating. This work
was made possible by DoE SBIR award DE-SC0020761.