Multilayer Nanostructured TiO₂/ZnO–PEDOT:PSS/Graphene–CNT/Epoxy Coating on AISI 316L Stainless Steel: Electrochemical, Mechanical, and Tribological Performance in Simulated Aggressive Urban Environments

Farrokhi, Amir; Shanaghi, Ali

doi:10.22075/imcf...

Multilayer Nanostructured TiO₂/ZnO–PEDOT:PSS/Graphene–CNT/Epoxy Coating on AISI 316L Stainless Steel: Electrochemical, Mechanical, and Tribological Performance in Simulated Aggressive Urban Environments

Articles in Press

Document Type : Original Paper

Authors

Amir Farrokhi ¹

Ali Shanaghi ²

¹ Department of Civil Engineering, Faculty of Civil Engineering and Architecture, Malayer University, Malayer, Iran.

² Department of Materials Engineering, Faculty of Engineering, Malayer University, Malayer, Iran

10.22075/imcf...

Abstract

Protecting structural metals in urban environments demands more than corrosion resistance in isolation — it requires a coating architecture that simultaneously addresses electrochemical attack, surface wetting, and mechanical wear. Here, a three-layer nanostructured system was assembled on AISI 316L stainless steel: a cathodically electrodeposited TiO₂/ZnO ceramic base, a spin-coated PEDOT:PSS/graphene intermediate film, and a CNT/epoxy nanocomposite outer shell. All specimens were evaluated in a pH ≈ 3 electrolyte combining 3.5 wt.% NaCl and 0.1 M H₂SO₄ — a composition designed to replicate the compounded stresses of acid rain, road deicing salts, and chloride-laden urban particulates. The results at each scale of analysis are consistent. FTIR spectroscopy and FESEM imaging confirm a defect-free, crack-free multilayer structure with nanocrystalline TiO₂/ZnO domains of 20–60 nm and no evidence of delamination. Electrochemical impedance spectroscopy reveals a coating resistance of Rcoat=50,900 Ω⋅cm2 within the first hour of immersion, retaining near-ideal capacitive behavior (n=0.81) after 24 h with corrosion rates suppressed below 0.008 mm/y — a reduction exceeding 93% relative to bare 316L. Contact angle measurements confirm a transition from hydrophilic steel (θ=68 ± 2°) to a superhydrophobic surface (θ=148±3°), remaining stable at 141±4° post-immersion, consistent with a durable Cassie–Baxter state. Nanoindentation yields the highest H/E ratio in the series (0.0726) alongside a stable friction coefficient of μ=0.14±0.02 over 12,000 s — 77% below that of uncoated steel. These findings collectively demonstrate that the multilayer hierarchical architecture, rather than any individual constituent, is the primary driver of the observed protective performance under aggressive simulated urban conditions.

Keywords

Multilayer nanostructured coating

AISI 316L stainless steel

Electrochemical impedance spectroscopy

Urban corrosion protection

Subjects