Comparisons of corrosion rates of Ni–P based composite coatings in HCl and NaCl solutions

The composite coatings of electroless Ni–P, Ni–P–PTFE, Ni–Cu–P and Ni–Cu–P–PTFE were prepared and their corrosion rates in HCl and NaCl solutions have been measured. The thickness and the compositions of the coatings were measured using a digital micrometer and an energy dispersive X-ray microanalysis (EDX), respectively. Surface morphology of the coatings was analysed by a scanning electron microscope (SEM). The incorporation of PTFE particles into Ni–P or Ni–Cu–P matrixes by gradually increasing the PTFE content from the substrate to the top surface improved the corrosion-resistant properties of the coatings significantly. The incorporation of copper into Ni–P or Ni–P–PTFE matrixes also improved the corrosion-resistant properties of the coatings.