Corrosion behaviour of equiatomic CoFeNi medium entropy alloy in molten chloride salts

The present work investigates the corrosion behavior of an equiatomic CoFeNi medium-entropy alloy in molten chloride salts. The CoFeNi alloy was prepared via mechanical alloying followed by furnace sintering at 1150℃. Single-phase face-centred cubic (FCC) solid solution with uniform distribution of constituent elements was observed in both the milled and the sintered alloy. Corrosion tests were conducted for 25 and 100 h in molten KCl-MgCl ₂ (60 − 40 mol%) at 600°C under an inert atmosphere, using commercial-grade Fe-based AISI 321 SS as a reference for comparison with the CoFeNi alloy. Weight loss is less for CoFeNi alloy compared to the AISI 321 SS after 100h of immersion in molten chloride salts. From the microstructural analysis, the CoFeNi alloy showed selective Fe depletion, along with void formation in intergranular and intragranular regions near the surface. While AISI 321 SS revealed spallation of corrosion products from the surface and grain boundary attack. The average corrosion depth of attack for the CoFeNi alloy after 100 h is 40.3 ± 2.76 µm, which is lower than that of AISI 321 SS. The aim of the present study is to understand and emphasise the corrosion behaviour of medium-entropy alloys in molten chloride salts and to improve their corrosion resistance in elevated-temperature molten-salt environments compared to traditional alloys.