Synergistic effect of peak current density and nature of surfactant on microstructure, mechanical and electrochemical properties of pulsed electrodeposited Ni-Co-SiC nanocomposites

Abstract

Ni-Co-nano SiC composite coatings were electrodeposited from a modified Watt's bath containing CTAB or SDS by pulse electrodeposition at four different peak current densities. The synergistic effect of the pulse peak current density and surfactant results in distinct morphological characteristics (characterized by SEM & TEM) and structural properties (characterized by XRD) producing nanocomposites with different mechanical (microhardness testing and nanoindentation testing) and electrochemical properties which can be traced to a multitude of factors such as nano SiC content and distribution, Cobalt content, grain refinement and texture. CTAB acts as a better dispersing agent for stabilising SiC nanoparticles compared to SDS, producing non-agglomerated SiC nanoparticles with a narrow size distribution. Increasing current density changes microstructure from spherical aggregates of polyhedral crystals (at 0.2 Acm−2) to uniform globular morphology (at 0.3 Acm−2) and finally to spherical aggregates (at 0.4 and 0.5 Acm−2), decreases cobalt content, increases SiC incorporation (up to a peak current density of 0.4Acm−2) and decreases coating thickness. Peak current density of the pulse electrodeposition is a vital factor in determining the crystallite size whereas both peak current density and nature of surfactant used are important factors in determining the texture. Electrodeposits with CTAB as surfactant provided higher values of hardness compared to SDS as surfactant, with C3 having the maximum hardness of 582 VHN because of nanosized grains and uniform dispersion of nano sized SiC. Nanocomposite electrodeposited using SDS as surfactant at a peak current density of 0.3Acm−2 has the highest corrosion resistance with a corrosion current density of 0.47 μAcm−2 and polarization resistance of 120.37 KOhm cm−2 in 3.5 wt% NaCl solution.