Role of Ti in regulating protective scale formation and corrosion resistance of FeNiCrAlTi Multi-principal element alloys in molten chloride salts

The corrosion behavior of Fe 46−x Ni 30 Cr 20 Al 4 Ti x multi-principal element alloys (MPEAs) (x = 0, 2, 4, and 6 at.%) in molten LiCl-KCl salt at 550 °C was systematically investigated, focusing on the role of Ti in enhancing corrosion resistance. The results suggest that TiO 2 may assist the heterogeneous nucleation of α-Al 2 O 3 . The Ti-containing MPEAs exhibited fewer voids and cracks in the oxide scale, together with a denser, more protective composite scale. The Ti-containing MPEAs formed a composite scale with an inner nanocrystalline layer of intergrown α-Al 2 O 3 and rutile TiO 2 , and an outer layer of Cr 2 O 3 columnar grains elongated along the predominant scale-growth direction. Concurrent grain refinement may additionally enhance the supply of scale-forming elements to the reaction interface. As the Ti content increased from 0 to 6 at.%, the corrosion rate after 100 h immersion decreased from 93.22 ± 7.87 to 42.58 ± 4.73 μm/y. Scale spallation was also markedly reduced. This work highlights TiO 2 -assisted α-Al 2 O 3 nucleation as a possible contributor to protective scale formation in molten chloride salts. It provides guidance for designing corrosion-resistant MPEAs for high-temperature molten-salt applications.