Eco-Friendly Ni-P-TiO2 Composite Coatings on AH36 Steel Using Plant-Extracted Nanoparticles for Marine Corrosion Resistance

Marine grade AH36 steel, widely used in offshore and shipbuilding industry, tends to suffer severe corrosion from aggressive marine condition. In order to improve its corrosion resistance and mechanical hardness this research deals with the development of electroless Ni-P composite coatings reinforced with TiO2 nanoparticles in three structural states: anatase, rutile and amorphous derived from plant extraction. A fourth hybrid specimen having all the three TiO2 phases was also examined. The coatings were deposited on AH36 steel and analyzed by Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD), Atomic Force Microscopy (AFM), microhardness measurement and electrochemical Tafel polarization measurement. The sample containing anatase coating had the best performance, showing up to 27 µm thickness. The results indicate a 13.5% increase in performance compared with the Ni–P sample, 67.4 nm surface roughness, and 200 HV (25% increase) microhardness. It also showed the highest corrosion resistance, with the maximum corrosion potential (–0.65 V) and lowest corrosion current density, which means the lowest corrosion in the sample. In comparison, the amorphous Titanium di oxide (TiO2) coating had a large surface roughness of 170.1 nm and lower coating thickness of 20 µm, where the hybrid sample was marked with the smallest coating thickness of 16 µm along with in homogeneous morphology. The rutile-type coating showed a mediocre performance with coating thickness of 24 µm and surface roughness of 106.6 nm. These results clearly demonstrate that the anatase phase is beneficial for homogeneous dispersal, large surface coverage and electrochemical protection. This work emphasises that TiO2 phase is crucial in developing efficient electroless composite coatings for marine steel.