Interstitials enable enhanced mechanical and anti-corrosion properties of a non-equiatomic quinary high-entropy alloy

Abstract

In this work, interstitial carbon has been employed to further enhance the mechanical and anti-corrosion properties of a metastable quinary Fe₄₀Mn₁₀Co₂₀Cr₂₀Ni₁₀ (at. %) high-entropy alloy (HEA). Both the C-free and C-doped (0.5 at. %) HEAs exhibit a face-centered cubic (FCC) single-phase structure after annealing. Upon tensile deformation, martensitic transformation prevails in the C-free alloy with the formation of hexagonal closed packed (HCP) phase, whereas dislocation slip and twinning are the dominant deformation modes in the C-doped HEA. Such shift of deformation mechanisms can be attributed to the carbon induced increase of stacking fault energy (SFE) (from ∼10 to ∼15 mJ/m²). Simultaneous increases of strength and ductility are achieved in this HEA system by carbon alloying. Carbon-induced interstitial solid solution strengthening effect contributes to the increased stress level, whereas the promoted twinning behavior contributes to the enhanced strain hardening ability. Besides, electrochemical corrosion analysis demonstrates that interstitial carbon reduces the active current density and accelerates the passivation process of the HEA upon immersion in 0.1M H₂SO₄ solution, contributing to the enhanced corrosion resistance. The findings offer insights into the design of strong, ductile and corrosion-resistant alloys.