Enhancing corrosion resistance of non-equiatomic FeNiCoCr high-entropy alloys via metalloid Si alloying

This study investigated the electrochemical corrosion behaviors of a Si-containing high strength and ductile non-equiatomic Fe₃₀Ni₂₀Co₂₀Cr₂₀Si₁₀ high-entropy alloy (HEA) with a single-phase solid solution structure in a 3.5 wt% NaCl solution. Compared to Si-free Fe₂₀Ni₂₀Co₂₀Cr₂₀Mn₂₀ and Fe₄₀Ni₂₀Co₂₀Cr₂₀ HEAs with identical Cr contents, the present HEA alloyed with metalloid Si shows prominent corrosion resistance with a significantly higher positive breakdown potential (∼1 V_SCE) and a lower current density (∼7.62 × 10⁻⁸ A/cm²). The elevated corrosion resistance is attributed to the reinforced stability of the passive film with modulated compositions by alloying of metalloid Si and elimination of Mn. The alloying of Si triggers the formation of (Fe, Cr)-mixed silicate in the passive film, yielding a high stability. In contrast, the presence of Mn oxides in the passive film of Fe₂₀Ni₂₀Co₂₀Cr₂₀Mn₂₀ degrades the anti-corrosion performance. These insights are useful for guiding the further development of strong and ductile alloys with superior anti-corrosion performance.