Bilayer carbonised polyacrylonitrile-epoxy coatings with enhanced anticorrosion and antiwear performance

This paper proposes a bilayer coating strategy for steel protection in which the carbon functional layer is formed in situ by carbonising polyacrylonitrile (PAN) directly on the substrate, hence eliminating the dispersion–agglomeration difficulties associated with nanofiller–epoxy composites. Raman spectroscopy revealed peak graphitic ordering at 2–2.5 w/v% PAN, which was supported by FT-IR findings of conjugated C═C/C═N structures. Thermal investigation revealed stability to around 600 °C, with a more practical glass transition at 63 °C. Contact angle measurements revealed that the carbon underlayer lowers hydrophobicity while maintaining barrier performance, implying that anticorrosion behaviour is determined by crosslink density, free volume, and diffusion tortuosity rather than surface wettability. EDS investigation ruled out substrate alteration during high-temperature processing as a factor affecting electrochemical performance. After a 60 day exposure to a 3.5 wt% NaCl solution, the P2.5-EP formulation demonstrated an impedance modulus (|Z|0.01 Hz) of 1.62 × 105 Ω cm2, approximately two orders of magnitude greater than that of bare steel, and a corrosion current density of 5.01 × 10−7 A cm−2, two orders lower than bare steel. P3-EP reduced wear rate by up to 79.86% and improved hardness from 127.7 ± 0.8 to 138 ± 1.1 HV10, shifting wear from adhesive/fatigue to mild abrasive. Since optimal anticorrosion and antiwear performance occur at different PAN concentrations (2.5 and 3 w/v%), this bilayer offers a tunable, scalable alternative to nanofiller–epoxy composites for corrosion and wear protection.