Effect of heat treatment on structures and corrosion characteristics of electroless Ni-P-SiC nanocomposite coatings

Ni-P-SiC nanocomposite coatings were successfully deposited onto mild steel substrates. The coating process was performed by sealing the specimens in an evacuated tempered glass tube and heated at various temperatures of 200 °C for 2 h, 400 °C for 1 h, and 600 °C for 10 min. The effect of heat treatment on the structures and corrosion characteristics of the electroless Ni-P-SiC nanocomposite coatings was investigated by atomic force microscopy (AFM), X-ray diffraction (XRD), Vickers hardness, cyclic polarization, and electrochemical impedance spectroscopy (EIS) analyses. AFM and XRD results indicate that the optimum grain diameters of Ni and SiC in the as-plated Ni-P-SiC nanocomposite coatings are approximately 96.8 and 49.1 nm, respectively. The maximum microhardness for the as-plated Ni-P-SiC nanocomposite coatings is 968.3 HV. The highest microhardness is achieved for the samples heat treated at 600 °C for 10 min because of the precipitation of NixPy phases and the formation of an inter-diffusional layer at the substrate-coating interface. The lowest corrosion current density value is obtained for the coatings heat treated at 400 °C for 1 h. EIS data confirm these results.