Properties of gradient Ni-P-PTFE coatings on stainless steel with different polytetrafluoroethylene concentrations

Ni-P-PTFE (polytetrafluoroethylene) coatings were prepared on stainless steel surfaces to enhance their anti-fouling performance. However, the coatings face the challenge of low adhesion strength due to the complex deposition conditions. To address this issue, gradient Ni-P-PTFE coatings with varying concentrations of PTFE emulsion were fabricated on stainless steels, and non-gradient Ni-P-PTFE coatings were also synthesized for comparison purposes. The surface morphology, cross-sectional morphology, and element distribution in the vertical direction were characterized using Scanning Electron Microscopy (SEM) and Energy-Dispersive Spectroscopy (EDS). X-ray Diffraction (XRD) was employed to examine the microstructure of the coatings. Nanoindentation was conducted to evaluate hardness and elastic modulus, while a friction and wear tester was used to measure the coefficient of friction. A coating adhesion scratch tester was utilized for testing the adhesion strength, whereas a contact angle tester determined wetting property characteristics. The results demonstrate that an increase in PTFE emulsion content leads to a reduction in the hardness and elastic modulus of Ni-P-PTFE coatings while gradually enhancing their hydrophobicity. The overall performance of gradient coatings surpasses that of non-gradient coatings. Notably, when the PTFE concentration reaches (25+50) mL/L, the gradient coatings exhibit uniform particle distribution, superior friction and wear resistance, and the bonding strength is enhanced.