Characterization of electrodeposited Ni–Cr/hBN composite coatings

In this study, Ni–Cr/hBN composite coatings with different hBN content were deposited on AISI 1040 mild carbon steel using electrodeposition. The coatings were characterized using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffractometry (XRD), cyclic voltammetry (CV), 2D surface profilometery, nano-indentation, corrosion and wear tests. While some cracks were observed in the Ni–Cr alloy coatings, more compact and crack-free surfaces were obtained in the Ni–Cr/hBN composite coatings under all deposition conditions. XRD analysis of the Ni–Cr/hBN layer revealed the presence of a predominant Ni phase with Cr, Cr2Ni3B6, (Ni2Cr23)0.16, and hBN phases in the structure. Depending on deposition parameters, the microhardness and nanohardness of the Ni–Cr and Ni–Cr/hBN coatings were found to range between 308 and 538 HV and 1,86–7,69 GPa respectively. hBN acted as a solid lubricant in the wear tests; the friction coefficient decreased and wear resistance was improved. Among the composite coatings, the corrosion resistance of the coating with 20 g/l hBN was found to be 12 and 3.3 times higher than the steel substrate and Ni–Cr alloy, respectively. The hBN additive provided better mechanical properties and corrosion resistance in the range of 5–20 g/l hBN, but after 20 g/l hBN agglomeration became a problem and impaired the mechanical properties. The highest corrosion and abrasion resistance was obtained with 20 g/l hBN.