An investigation on effects of heat treatment on corrosion properties of Ni–P electroless nano-coatings

Electroless Ni–P coatings are recognized for their excellent properties. In the present investigation electroless Ni–P nano-crystalline coatings were prepared. X-ray diffraction technique (XRD), scanning electron microscopy (SEM), potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) were utilized to study prior and post-deposition vacuum heat treatment effects on corrosion resistance together with the physical properties of the applied coatings. X-ray diffraction (XRD) results indicated that the As-plated had nano-crystalline structure. Heat treatment of the coatings produced a mixture of polycrystalline phases. The highest micro-hardness was achieved for the samples annealed at 600 °C for 15 min due to the formation of an inter-diffusional layer at the substrate/coating interface. Lower corrosion current density values were obtained for the coatings heat treated at 400 °C for 1 h. EIS results showed that proper heat treatments also enhanced the corrosion resistance, which was attributed to the coatings’ structure improvement.