Achieving superior corrosion protection of Cr(III)-ZrC composite coatings through nonionic-surfactant-mediated ZrC dispersion

Trivalent chromium (Cr(III)) electrodeposition is regarded as an environmentally benign alternative to hexavalent chromium plating, but the protective performance of Cr(III)-ZrC composite coatings can be limited by ZrC nanoparticle agglomeration and non-uniform incorporation. In this work, the nonionic surfactant Synperonic F108 (SF) was introduced for the first time into a Cr(III)-ZrC composite electrodeposition system to regulate ZrC dispersion and improve coating uniformity and corrosion resistance. SF was proposed to form a steric stabilization layer on ZrC nanoparticles, and the dispersion results were consistent with reduced agglomeration and more homogeneous incorporation into the Cr(III) matrix. At an optimal SF concentration of 0.5 g/L, the dynamic light scattering (DLS)-measured median agglomerate size of ZrC decreased from 268 to 139 nm, and scanning Kelvin probe force microscopy (SKPFM) revealed the lowest surface-potential standard deviation of 9.04 mV, indicating improved dispersion and reduced local electrochemical heterogeneity. Consequently, compared with the SF-free coating, the corrosion current density of the 0.5 g/L SF coating decreased by 90.5%, from 5.39 to 0.51 μA·cm −2 , while its charge-transfer resistance increased to 69.7 × 10 4  Ω·cm 2 . Time-dependent electrochemical impedance spectroscopy and an 80-day scratched immersion test in 3.5 wt% NaCl solution further confirmed the superior long-term protective performance of the optimized coating. The enhanced performance is consistent with reduced agglomeration-induced defects, improved microstructural uniformity, and reduced local electrochemical heterogeneity, which may contribute to limiting preferential electrolyte ingress during long-term exposure. These findings demonstrate that surfactant-mediated dispersion regulation is an effective strategy for improving Cr(III)-based composite coatings.