Microstructure and corrosion behaviour of pulse electrodeposited Ni-TiO₂/graphene composite coating on SS316L

This study investigates Ni-TiO₂/X graphene (X = 0, 0.1, 0.2, and 0.3 g/L ) composite coatings deposited on SS316L substrates using the pulse current electrodeposition (PCE) process. The surface morphology and coating characteristics were examined using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), Vickers microhardness testing, and electrochemical corrosion analysis to evaluate chemical composition, phase formation, microstructure, mechanical properties, and electrochemical corrosion behaviour. XRD results showed that increasing graphene content leads to peak broadening and a slight peak shift, indicating grain refinement in the coated samples. The major diffraction peaks of Ni were observed at 44.6°, 52.2°, and 78.3°, confirming the presence of the FCC Ni phase. The Ni-TiO₂-0.2Gr coating exhibited the minimum crystallite size of 17.81 nm. Microstructural observations revealed that the addition of 0.2 g/L-graphene produces a more homogeneous and compact coating structure compared to other compositions. Microhardness measurements indicated that the Ni-TiO₂-0.2Gr coating achieves the highest hardness value of 582.6 HV, compared to 534 HV for 0.3 g/L of graphene and 290 HV for coatings without graphene. Among all the coatings studied, the Ni–TiO₂–0.2Gr composite coating exhibited the best corrosion resistance in NaCl solution, as evidenced by its minimum corrosion current density (6.88 × 10⁻⁶ A/cm²) and maximum protection efficiency (95.71%). The enhanced corrosion protection offered by this coating was primarily due to its denser microstructure. The refined microstructure and uniform graphene dispersion contribute to enhanced mechanical strength and reduced surface degradation. Overall, the Ni-TiO₂/graphene composite coatings produced through PCE exhibit a fine microstructure, improved hardness, and superior corrosion resistance, indicating their suitability for surface protection applications.