CHARACTERIZATION AND MICROHARDNESS OF ELECTRODEPOSITED Ni–W COATINGS OBTAINED FROM GLUCONATE BATH

Ni–W alloy coatings are electrodeposited with direct and pulse current using gluconate bath at pH5. Effects of direct current (DC) and pulse current (PC) on structural characteristics of the coatings have been investigated by energy dispersive X-ray spectroscopy (EDXS), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), differential scanning calorimetry (DSC) and X-ray photoelectron spectroscopy (XPS). EDXS shows that W contents are 13.3 and 12.6 at.% in DC and PC (10:40) Ni–W coatings, respectively. FESEM analysis exhibits the homogeneous coarse nodular morphology in DC plated deposits. DSC studies reveal that Ni–W coatings are thermally stable up to 400°C. XPS studies demonstrate that DC plated coating has significant amount of Ni and W in elemental form along with their respective oxidized species. In contrast, mainly oxidized metals are present in the as-deposited coatings prepared with PC plating. The microhardness of pulse current (100:400) deposited Ni–W coating is about 750 HK that is much higher than DC plated coating (635 HK). Heat treatment of the deposits carried out at different temperatures show a significant increase in microhardness which can be comparable with hard chromium coatings.