Time Evolution of Passive Behavior on CoCrFeNi High-Entropy Alloy
摘要
As a paradigmatic example in the development of new corrosion-resistant materials, the CoCrFeNi high-entropy alloy possesses a single-phase fcc solid solution structure that effectively prevents the occurrence of localized corrosion, thereby exhibiting outstanding corrosion resistance. Investigations into corrosion resistance mechanisms have identified the inhibition of electron transfer and ion migration by the passive film as the primary origin of this property. This study focuses on the growth process of the passive film on the corrosion surface of the complex multi-component CoCrFeNi HEA. The results indicate that during potentiostatic polarization at 0.25 V versus Ag/AgCl, the passive film on the CoCrFeNi high-entropy alloy formed rapidly within 0.5 h and completely covered the alloy substrate. Subsequently, the film underwent thickening and flattening stages, and its properties stabilized after approximately 6.5 h; the corrosion current density of the passive film in this stable state was approximately 8.6 nA/cm2. Following 12 h of potentiostatic polarization, the passive film exhibited a bilayer structure composed of oxides and hydroxides of Cr and Fe. Specifically, the surface layer at depths of 1–3 nm was enriched in Cr, while the sub-surface layer at depths of 4–7 nm was enriched in Fe. These insights into the growth of the passive film provide a valuable reference for the regulation of passivation behavior and the optimization of corrosion resistance in future, more complex HEAs.