Electrophoretic coating of nano NiAl₂O₄–NiCr₂O₄ on 304 stainless steel: effect of coating voltage and time on the properties

The coating of metals with nanoceramics to improve their functional properties can be achieved by electrophoretic deposition (EPD). The coating of chromiumnickel oxide by EPD was investigated to study the EPD parameters on the coating on 304 stainless steel. The EPD voltage and coating time varied from 50 to 150 V and 1 to 3 min, respectively, and were sintered at 750°C. Various analyses were performed, including Fourier transform infrared spectroscopy, X-ray diffraction, field emission scanning electron microscopy, ball-on-disk wear, microhardness, and corrosion tests. The weight of the coating increased with EPD time and voltage, reaching the maximum (8.82 mg/cm³) at 120 V⁻³ min. At 110 V, the coatings were less cracked. The quasi-spherical NiAl₂O₄/NiCr₂O₄ agglomerates (1.5 μm average size) with embedded nickel nanoparticles (15–20 nm) contributed to the improved wear resistance of the coated samples. The coating showed the best wear resistance at 110 V⁻³ min (31% improvement in wear rate); however, all coatings had promising wear resistance at 110 V. The coating at 100 V⁻³ min had the highest corrosion resistance (5.19 kΩ·cm²) compared with the other coatings, which is due to its thicker, less porous structure. According to electrochemical impedance analysis, the coated sample has a two-time constant in the circuit.