Corrosion resistance and hardness characteristics of electrodeposited ternary black Ni-Cu-Co alloy coatings

An attempt has been made to develop a novel ternary Ni-Cu-Co coatings with improved corrosion resistance and micro hardness values. XRD and XPS studies have proved that the enhancement of corrosion resistance and hardness by coating after annealing at 300°C could be due to the formation of Ni3Cu5, CuO and NiO and confirmed from the appearance of core peaks at Co 2p3/2, Cu 3p, Cu 3p3/2, Ni 2p3/2 and Ni 2p with binding energies of 785 eV, 45 eV, 933 eV, 853 eV and 839 eV respectively. The formation of uniform layer of Ni-Cu-Co coatings is evident from SEM images. The coatings offered the corrosion resistance of 40 times of uncoated mild steel surface in 3.5% NaCI. The reduction of Ecorr, Icorr, Cdl and enhancement of Rt value from polarization and impedance measurement indicated the corrosion resistance ability of Ni-Cu-Co black coatings. © 2013 University of Manchester and the authors.