CoCrFeMnNi high entropy alloys (HEAs) were additively manufactured (AM) by laser powder bed fusion and their corrosion resistance in 3.5 wt% NaCl solution was studied by potentiodynamic polarization and electrochemical impedance spectroscopy tests. A systematic study of AM CoCrFeMnNi HEAs’ porosity under a wide range of laser processing parameters was conducted and a processing map was constructed to identify the optimal laser processing window for CoCrFeMnNi HEAs. The near fully dense AM CoCrFeMnNi HEAs exhibit a unique non-equilibrium microstructure consisting of tortuous grain boundaries, sub-grain cellular structures, columnar dendrites, associated with some processing defects such as micro-pores. Compared with conventional as-cast counterpart, the AM CoCrFeMnNi HEAs showed higher pitting resistance (ΔE) and greater polarization resistance (R_p). The superior corrosion resistance of AM CoCrFeMnNi HEAs may be attributed to the homogeneous elemental distribution and lower density of micro-pores. Our study widens the toolbox to manufacture HEAs with exceptional corrosion resistance by additive manufacturing.

Dual-phase high entropy alloys have recently attracted widespread attention as advanced structural materials due to their unique microstructure, excellent mechanical properties, and corrosion resistance. However, their molten salt corrosion behavior has not been reported, which is critical in evaluating their application merit in the areas of concentrating solar power and nuclear energy. Here, the molten salt corrosion behavior of AlCoCrFeNi_2.1 eutectic high-entropy alloy (EHEA) was evaluated in molten NaCl-KCl-MgCl₂ salt at 450 °C and 650 °C in comparison to conventional duplex stainless steel 2205 (DS2205). The EHEA showed a significantly lower corrosion rate of ~1 mm/year at 450 °C compared to ~8 mm/year for DS2205. Similarly, EHEA showed a lower corrosion rate of ~9 mm/year at 650 °C compared to ~20 mm/year for DS2205. There was selective dissolution of the body-centered cubic phase in both the alloys, B2 in AlCoCrFeNi_2.1 and α-Ferrite in DS2205. This was attributed to micro-galvanic coupling between the two phases in each alloy that was measured in terms of Volta potential difference using a scanning kelvin probe. Additionally, the work function increased with increasing temperature for AlCoCrFeNi_2.1, indicating that the FCC-L1₂ phase acted as a barrier against further oxidation and protected the underlying BCC-B2 phase with enrichment of noble elements in the protective surface layer.

Refractory high-entropy alloys (RHEAs) have recently attracted widespread attention due to their outstanding mechanical properties at elevated temperatures, making them appealing for concentrating solar power and nuclear energy applications. Here, the corrosion behavior of equimolar HfTaTiVZr and TaTiVWZr RHEAs was investigated in molten FLiNaK eutectic salt (LiF-NaF-KF: 46.5−11.5−42 mol.%) at 650 °C. Potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and immersion test measurements were carried out for these two RHEAs and compared with Inconel 718 (IN718) superalloy and SS316 stainless steel under identical test conditions. Both TaTiVWZr and HfTaTiVZr refractory high-entropy alloys exhibited an order of magnitude lower corrosion rate than SS316. IN718 and TaTiVWZr showed similar corrosion rates. Corrosion products enriched with noble alloying elements formed in the case of TaTiVWZr and IN718 were stable and protective on the substrate. SS316 showed the lowest corrosion resistance and void formation along the exposed surface due to the active dissolution of Cr and Fe, which provided diffusion paths for the corroded species. The surface analysis results showed that IN718 underwent pitting corrosion, while TaTiVWZr experienced selective dissolution in the inter-dendritic area. In contrast, HfTaTiVZr and SS316 experienced corrosion at the grain boundaries.