Chromium-based functional coatings (CFCs) are widely recognized for their outstanding wear and corrosion resistance across diverse industrial sectors. However, despite advancements in deposition techniques and microstructural enhancements, many contemporary CFCs remain vulnerable to degradation in highly corrosive environments. For the first time, this research delivers a thorough characterization of the corrosion resistance of advanced CFCs, focusing on the performance of a 5 μm thin dense chromium (TDC) coating. These TDCs exhibit a distinctive, uniform nodular microstructure, characterized by approximately 3.6 μm nodules composed of defect-free near-nanocrystalline grains (227 ± 75 nm) plus enhanced electrochemical nobility. This structure promotes the rapid formation of a stable, dense bilayer oxide, resulting in a remarkably low corrosion susceptibility, effectively impeding both charge transfer and mass transport, particularly the diffusion of Cl^- ions. Furthermore, the coating sustains an exceptionally high polarization resistance over extended exposure times in aqueous NaCl electrolyte. These findings offer critical insights into the design of CFCs optimized for extreme environmental durability.

Chromium coatings, famed for their superior wear and corrosion resistance, are a critical component in countless industrial processes. However, the longevity of these coatings in aggressive corrosive environments continues to be a significant hurdle, even with recent advances in deposition technology and microstructural improvements. An advanced thin dense chromium (TDC) coating, with a near-nanocrystalline structure and unique morphology, naturally forms a non-conductive nano-bilayer oxide. This passive and protective layer effectively moderates electrical charge transfer, offering superior corrosion resistance. X-ray photoelectron spectroscopy (XPS) shows significant Cr³⁺ oxide layer formation, distinguished by multiplet splitting, after 7 days in a 0.6 M NaCl solution. The unique characteristics of this non-conductive bilayer oxide structure promote its growth and densification, leading to vertical differential charging in the O1s electron energy region. This effect arises from the enhanced resistivity of the oxide layer. Electrochemical impedance spectroscopy (EIS) confirmed these findings, showing a substantial increase in charge transfer resistance at the chromium metal/bilayer oxide interface, reaching 1.01 MΩ. Scanning Kelvin probe force microscopy (SKPFM) analysis shows that both TDC nodules and their boundaries exhibit high surface potential and work function. However, after exposure to NaCl media, these values are moderately reduced, likely due to diminished electrical surface charge distribution.