Influence of nanoparticles concentrations on Cr-C-Al2O3 and Cr-C-SiC nanocomposite coatings electrodeposited from trivalent chromium bath

In the current study, Cr-C-Al2O3 and Cr-C-SiC nanocomposite coatings were electrodeposited on copper substrates using a modified trivalent chromium electroplating bath containing 80 nm Al2O3 and 50 nm SiC powder, respectively. The influence of concentrations of Al2O3 and SiC nanoparticles on the coatings' crystalline structure, surface morphology, hardness, and corrosion behavior were studied. The crystalline structure, composition, and surface morphology of the coatings were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and energy-dispersive X-ray spectroscopy (EDX). The corrosion resistance test was carried out by the potentiodynamic polarization method. The microhardness was studied via Vickers Microhardness Test. The incorporation of Al2O3 and SiC nanoparticles into the Cr matrix is critical in enhancing microhardness. From the EDX analysis, it was determined that the highest weight percentage (wt%) of Al2O3 and SiC nanoparticles in the Cr-C- Al2O3 and Cr-C-SiC nanocomposite coatings was deposited from the baths containing 40 g/L Al2O3 and SiC, respectively. Moreover, the Cr-C-Al2O3 and Cr-C-SiC nanocomposite coatings achieved the highest hardness values at concentrations of 40 g/L Al2O3 and 10 g/L SiC, respectively. The addition of nanoparticles enhanced the hardness of the coatings by 17% (Cr-C-Al2O3) and 13% (Cr-C-SiC) compared to the as-plated chromium coating. The study highlights the dispersion hardening effect of the nanoparticles, which effectively strengthens the nanocomposite coatings. However, the incorporation of agglomerated nanoparticles formed surface defects, such as microholes and gaps in the coatings, reducing their corrosion resistance. This was evidenced by a shift in corrosion potential (Ecor) towards more negative values and an increase in the corrosion current density (icor). Notably, increasing the Al2O3 concentration increased particle content and microhardness in the Cr-C-Al2O3 nanocomposite coatings, whereas this effect was not observed for Cr-C-SiC nanocomposite coatings. The hardness of the Cr-C-SiC coatings exhibited a decrease as the nanoparticle concentration increased, primarily due to the poor wettability of SiC particles. This led to the agglomeration of particles and the formation of a defective microstructure. In addition, this study presents a novel approach for the electrodepo-sition of Cr-C-Al2O3 and Cr-C-SiC nanocomposite coatings, effectively incorporating Al2O3 and SiC nano -particles into the chromium matrix. The investigation of nanoparticle concentrations and their impact on the crystalline structure, surface morphology, hardness, and corrosion resistance provides valuable insights for the development of nanocomposite coatings with enhanced mechanical and protective properties.