Microstructural and Mechanical Assessment of Pulse-Reverse Plated Cobalt Matrix Nanocomposite Coatings

Electrodeposited metal matrix nanocomposites (MMNCs) offer improved mechanical properties for tribological coatings. The development of nanotechnology in the last 25 years means there are now a multitude of nanoparticles, nanowires and nano-tubes available in an ever- increasing range of materials and hence the scope for new nanocopmosites coatings by electrodeposition is greater than ever, with the potential to develop a coating with functional performance equivalent to hard chrome. Recent work on pulse reverse deposition of MMNCs by Weston, et al has suggested the capability to control the co-deposition of metals and particulates. The technique includes the use of a surfactant and pulse reverse plating (PRP). In the present work, the suggested mechanism investigated on cobalt matrix nanocomposites with a number of particles including SiC, Al2O3, and PTFE with different particles loading and size. The produced nanocomposites assessed microstructurally and mechanically by different analysis: Field emission gun scanning electron microscopy FEGSEM cross section and surface topography, Energy Disperse X-ray EDX, image analysis, X-ray diffraction XRD, and transmission electron microscopy TEM. The microstructural results indicated the applicability of PRP for Co-SiC with different particle loadings, and for Co-SiC with 5 g l-1 Al2O3. The mechanical properties of the produced coatings suggests an increase in microhardness with increasing the particles volume fraction with 8.7 vol. % of SiC increasing the hardness by up to 25 % and 9.1 vol% of Al2O3 raising it by up to 31 % beyond the hardness of the pure Co coatings. No significant effect attributed to the reduction of the grain size was observed. A predictive model for the main controlling strengthening (dispersion strengthening) of the nanocomposites with low surfactant content 0.2 g l-1 of SDS was found. The model is applicable on both nanocomposites electroplated cobalt coatings Co-Al2O3 and Co-SiC.