Corrosion-Resistant Multi-principal Ni₆₀Cr₁₅Co₁₅Ti₅Al_2.5Nb_2.5 Alloy: Loss of Passivation (LOP) and Recovery of...

This study explores the corrosion behavior of a nonequiatomic Ni₆₀Cr₁₅Co₁₅Ti₅Al_2.5Nb_2.5 high-entropy alloy (HEA) subjected to thermal aging. Electrochemical testing in 3.5 wt% NaCl solution revealed that short-term aging (≤1 h) induces a loss of passivation (LOP), marked by a corrosion potential drop to -260 mV_SCE and an increase in corrosion current density (i _corr) to 2.7 μA/cm². In contrast, prolonged aging (≥10 h) promotes a recovery of passivation (ROP), driven by microstructural elemental redistribution. This recovery is evidenced by a positive shift in corrosion potential to -125 mV_SCE, a significant reduction in i _corr to 7.1 × 10^-2 μA/cm², and an increase in pitting potential (E _pit) from 413 mV to 495 mV. Electrochemical impedance spectroscopy (EIS) further confirmed enhanced passivity through a reduction in effective capacitance (from 3.2 to 2.6 μF/cm²) and an increase in polarization resistance (from 960 to 1084 kΩ·cm² ). However, excessive aging (>50 h) may trigger a secondary LOP. An optimal aging window (30-50 h) yields a stable and protective passive film.