Abstract:Properties of Si₃N₄/Ni electroplated nanocomposite such as corrosion current density after long time immersion, roughness of obtained layer and distribution of nanometric particulates were studied. Other effective factors for fabrication of nanocomposite coatings were fixed for better studying the effect of the average size of nanoparticulates. The effects of the different average size of nanometric particulates (ASNP) from submicron scale (less than 1 µm) to nanometric scale (less than 10 nm) were studied. The nanostructures of surfaces were examined by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM). Corrosion rates of the coatings were determined using the Tafel polarization test. It is seen that decreasing the ASNP will lead to lower corrosion current densities; however, in some cases, pitting phenomena are observed. The roughness illustrates a minimum level while the distribution of nanometric particulates is more uniform by decreasing the ASNP. The effects of pulsed current on electrodeposition (frequency, duty cycle) and concentration of nanoparticulates in electrodeposition bath on trend of obtained curves have been discussed. Response surface methodology was applied for optimizing the effective operating conditions of coatings. The levels studied were frequency range between 1 000 and 9 000 Hz, duty cycle between 10% and 90% and concentration of nanoparticulates of 10−90 g/L.

Key words: corrosion; electrodeposition; nanocomposite; nanostructure; nano diamond