Microstructural and mechanical assessment of pulse-reverse plated cobalt matrix nanocomposite coatings

• Main Author: Albusalih, Dhuha F.
• Other Authors: Gill, Simon ; Weston, David
• Published: University of Leicester 2018
• Subjects: 620
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.762639

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.