Applying Ni-P-PTFE Composite Coatings by Electroless Deposition Method and Investigating Their Corrosion and Tribological Properties

To develop and improve some of the electroless nickel coating properties, nickel composite electroless coatings were introduced. In this research, Ni-P-PTFE composite coatings containing different PTFE percentages were deposited on steel substrate by electroless method. The influence of amount of PTFE on the mechanical, anti- corrosive and tribological properties of coatings was investigated. The Micro hardness and pin on disk analysis were carried out to evaluate the hardness, erosion resistance and friction coefficient of coatings. Scanning electron microscopy (SEM) and Energy dispersive X-ray spectroscopy (EDX) were performed to study the morphology and elements of coatings. The results showed in the absence of PTFE the amount of P element was about 10.42 wt.% whilst it decreased to 5.02 wt.% in the presence of 20 g/l PTFE. In addition, the presence of PTFE lubricant particles reduced the friction coefficient from 0.8 for Ni-P coating to 0.1 for Ni-P-PTFE (20g/l) composite coatings. In bath containing concentrations of 20g/l PTFE, respectively, the lowest coefficient of friction was observed. The anti-corrosive behavior of coatings was studied in 3.5 wt. % NaCl by tafel polarization and electrochemical impedance spectroscopy (EIS) methods. Evaluating the effect of PTFE concentration on the corrosion behavior of the composite coatings demonstrated that the obtained coatings in presence of 20 g/L PTFE had the maximum corrosion resistance. For example, the OCP number increased from -475 mV to -350 mV. Moreover, the logarithm of the corrosion current density decreased from 1.78 μA.cm-2 to 1.15 μA.cm-2. It was due to the proper distribution of PTFE particles in coating and their chemical stability.