Electrodeposition and Characterization of Cr-MoS2 Composite Coatings

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In this study, Cr-MoS2 composite coatings were electrodeposited from conventional Cr+6 baths containing different amounts of MoS2 particles and various types of surfactant (cationic and anionic). The effect of bath chemical composition on the coatings properties like their microstructure, morphology, chemical composition, corrosion behavior, surface roughness and microhardness was investigated using x-ray diffraction, scanning electron microscopy (SEM), energy-dispersive x-ray analysis, potentiodynamic polarization, electrochemical impedance spectroscopy, surface profilometry and Vickers microhardness measurement techniques, respectively. The results showed that incorporation of MoS2 particles into the composite coatings is very limited and Cr matrix with very low crystallinity will be electrodeposited at various experimental conditions. The presence of MoS2 particles in the bath (up to an optimum value) leads to the formation of the composite coatings with lower surface roughness values than that of conventional chromium coating. Although more MoS2 particles will be incorporated into the electrodeposits when the solid content of the bath increases, chromium cannot be electrodeposited from baths containing high amounts of MoS2 particles. Application of cationic surfactant promotes incorporation of particles into the Cr metallic matrix. Moreover, the presence of surfactant in the bath results in the formation of coatings with less microcracks. All the composite coatings have more hardness values than that of conventional chromium coating; maximum hardness is attributed to the coatings that were electrodeposited from baths containing no surfactant. The corrosion test results revealed that the smooth coatings containing more MoS2 particles and less microcracks exhibit more corrosion resistance than the other ones.