Effect of Polytetrafluoroethylene (PTFE) Content on the Properties of Ni-Cu-P-PTFE Composite Coatings

Q235B mild steel has the advantages of good mechanical properties, welding properties, and low cost, and it is widely used in bridges, energy fields, and marine equipment. However, Q235B low-carbon steel is prone to serious pitting corrosion in urban water and sea water with high chloride ions (Cl^-), which restricts its application and development. Herein, to explore the effects of different concentrations of polytetrafluoroethylene (PTFE) on the physical phase composition, the properties of Ni-Cu-P-PTFE composite coatings were studied. The Ni-Cu-P-PTFE composite coatings with PTFE concentrations of 10 mL/L, 15 mL/L, and 20 mL/L were prepared on the surface of Q235B mild steel by the chemical composite plating method. The surface morphology, elemental content distribution, phase composition, surface roughness, Vickers hardness, corrosion current density, and corrosion potential of the composite coatings were analyzed by scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), X-ray diffraction (XRD), three-dimensional profile, Vickers hardness, electrochemical impedance spectroscopy (EIS), and Tafel curve test methods. The electrochemical corrosion results showed that the corrosion current density of the composite coating with a PTFE concentration of 10 mL/L in 3.5 wt% NaCl solution was 7.255 × 10^-6 A∙cm^-2, and the corrosion voltage was -0.314 V. The corrosion current density of the 10 mL/L composite plating was the lowest, the corrosion voltage positive shift was the highest, and the EIS arc diameter of the 10 mL/L composite plating was also the largest, which indicated that the 10 mL/L composite plating had the best corrosion resistance. Ni-Cu-P-PTFE composite coating significantly enhanced the corrosion resistance of Q235B mild steel in 3.5 wt% NaCl solution. This work provides a feasible strategy for an anti-corrosion design of Q235B mild steel.