Characterization and microhardness of Ni−W−P coatings electrodeposited with gluconate bath

Abstract

Ni−W−P coatings are electrodeposited from an acid gluconate bath and the effect of P addition to deposits is characterized by various physicochemical techniques. The effect of direct current (DC) and pulse current (PC) deposition modes on the structure, morphology, surface roughness, and elemental oxidation states of Ni−W−P coatings is studied in detail. X-ray diffraction (XRD) patterns of Ni−W−P coatings display the formation of an amorphous structure, which is influenced by the addition of phosphorus. Results obtained from field emission scanning electron microscopy (FESEM) images reveal the appearance of homogeneous coarse nodular morphology for electrodeposited Ni−W−P coatings devoid of cracks. X-ray photoelectron spectroscopy (XPS) studies of Ni−W−P coatings indicate the presence of metallic and oxidized Ni species in DC-plated coatings, whereas oxidized Ni species dominate in PC-plated coatings. Microhardness of as-deposited DC Ni−W−P coatings increases as the phosphorus content increases, whereas the microhardness is similar for all PC Ni−W−P coatings. The effect of heat treatment on the structure and microhardness of the deposits carried at different temperatures shows a substantial increase in microhardness which is comparable with hard chromium coating.