Investigation of mechanical properties and corrosion behavior of (FeNi)80-2xCr20AlxTix multi-principal-element alloys in molten chloride salts

To improve the corrosion resistance of FeNiCr-based alloys in molten chlorides, Al and Ti were introduced as co-alloying elements with equal atomic contents of 0-10 at.%. This study examines the effects of Al-Ti co-alloying on the microstructural evolution, room-temperature mechanical properties, and corrosion behavior of FeNiCr-based alloys in molten 45LiCl-55KCl (wt.%) salt at 550 °C. Al and Ti contents of 5-7.5 at.% each provide the balance between mechanical properties and molten-salt corrosion resistance. Within this compositional range, the alloys achieve high ultimate tensile strengths of 622-973 MPa while retaining tensile elongations of 20-51%. After 100 h of immersion, the Al 5 Ti 5 alloy shows 62% lower corrosion rate than the Al/Ti-free alloy, and its corrosion depth decreases from 19.2 μm to 5.9 μm. Thermodynamic calculations and microstructural characterizations reveal that the improved corrosion resistance arises from the formation of a compact Al 2 O 3 -TiO 2 -Cr 2 O 3 composite scale. This scale suppresses the outward dissolution of metal cations and limits the inward transport of corrosive species. These findings clarify the role of Al-Ti co-alloying in regulating oxide-scale formation in molten chlorides and provide a compositional design strategy for corrosion-resistant structural alloys used in high-temperature molten-salt environments.