This study investigates the combination of dopamine (DA) and tyrosinase (TYR) for corrosion protection of carbon steel in acidic conditions, focusing on corrosion protection behavior and film formation mechanisms. Confocal Raman microscopy analysis demonstrated that DA forms a thin protective film on carbon steel through complexation with Fe ions, preferably at defect sites, thereby transforming mixed Fe oxides to Fe(catechol)3, while TYR promotes DA oxidation and enhances the complexation. Surface coverage of Fe(catechol)3 increases from 37 % at 10 min to 89 % at 60 min of exposure in the DA/TYR solution. Inductively coupled plasma-optical emission spectroscopy (ICP-OES) measurements showed a 25 % reduction in Fe release after 48 h in the DA/TYR solution. X-ray photoelectron spectroscopy (XPS) analysis revealed that TYR promotes oxidation from Fe2+ to Fe3+ at the surface, resulting in a thinner yet more protective DA-Fe complexation film. The DA/TYR system increased corrosion resistance by 47 % after 24 h, primarily attributed to the rapid and extensive formation of Fe (catechol)3 complexes between DA and Fe ions released from the substrate, further strengthened by TYR. This bio-inspired and green corrosion inhibitor strategy, combining DA's metal-binding affinity with TYR's enzymatic oxidation capability, provides a scalable and non-toxic strategy for effective corrosion protection.

New materials for wear and corrosion protection are being explored in the family of high entropy alloys. However, there is limited work on wear-corrosion synergies of these alloys, particularly for magnetron sputtered thin films, where nanoscale morphology and defects strongly affect the performance and often yield different behaviors than for bulk counterparts. In this work, CoCrFeMnNi is tested as a protective thin film under non-ideal conditions. Wear-corrosion synergies are explored for films with and without low nanometer-scale voids. The influence of corrosion on wear is tested by microtribology on pre-corroded samples, while the influence of voids and wear on corrosion is tested by electrochemical tests of pre-worn and non-worn samples during optical microscopy in 3.5% NaCl solution. 1–10 nm wide intercolumnar voids cause the formation of a millimeter-scale zone of accelerated dissolution inside the film, which propagates between columns. Anodic polarization causes an electrochemically driven delamination of the coatings. Pre-scratching of the films does not alter this corrosion mechanism significantly, except for preferential initiation of delamination at the wear track. After corrosion, the wear rate is increased by up to 320% for voided films and decreased by up to 50% for the dense films. This work provides a more realistic view of the strength and limitation of magnetron sputtered high entropy alloys as protective coatings.

Passivity is essential for corrosion resistance of Fe- and Ni-based alloys and is governed by the formation of nanometer-scale passive films that suppress metal dissolution. This study examines passive film evolution under anodic polarization up to the transpassive region for Fe-base Ni-rich Sanicro 35 (Fe–Ni–Cr–Mo) and Ni-base Alloy 718 (Ni–Fe–Cr–Nb–Mo) under acidic chloride conditions. Using synchrotron AP-XPS, GD-OES, ICP-OES, and UV–Vis spectroscopy, passive film composition, oxide growth and metal dissolution were investigated across the applied anodic potential region. Sanicro 35 forms a thicker Cr-rich passive film consisting of mainly oxides of Cr, Fe, Mo, with sustained Cr replenishment but transpassive breakdown occurs at 1.0 V (Ag/AgCl), accompanied by CrVI release. Alloy 718 suffers some pitting attack, but remains largely passive up to  1.4 V, developing a thinner passive film consisting of mainly oxides of Cr, Fe, Mo and Nb, with Mo- and Nb-enrichment and Cr depletion at high potentials. The results demonstrate that transpassive behavior is controlled by the interplay of Cr, Mo, and Nb within the oxide rather than bulk Cr, Fe or Ni content alone, providing insights for alloy design in aggressive environments.