Tribological Behavior and Corrosion Resistance of Electroless Ni-B-W Coatings

Abstract

The present study considers the tribological behavior and corrosion resistance of electroless Ni-B-W coatings deposited on AISI 1040 steel substrates. Coating is characterized using scanning electron microscopy, energy dispersive X-ray analysis and X-ray diffraction technique. In as-deposited condition, coatings are found to be amorphous. On heat treatment, precipitation of crystalline Ni (1 1 1) and its borides take place. For as-deposited coating, the microhardness is obtained as [Formula: see text]759[Formula: see text]HV[Formula: see text] which increases to [Formula: see text]1181[Formula: see text]HV[Formula: see text] and [Formula: see text]1098[Formula: see text]HV[Formula: see text] when heat treated at 350[Formula: see text]C and 450[Formula: see text]C, respectively. Incorporation of W in Ni-B coating results in an increase of hardness by 89[Formula: see text]HV[Formula: see text] in as-deposited condition. Heat treatment also results in increase in crystallite size of Ni (1 1 1). Wear rate and coefficient of friction (COF) of the coatings are evaluated on a pin-on-disc setup under both dry and lubricated sliding conditions. Wear resistance is observed to improve on heat treatment with an increase in crystallite size while COF deteriorates. However, in as-deposited condition, wear rate and COF of Ni-B-W coatings improve by [Formula: see text]5 and [Formula: see text]3 times, respectively, compared with Ni-B coatings. Wear and friction performance of the coatings are enhanced under lubrication due to the columnar structure of the coatings that retain lubricants. Corrosion resistance of Ni-B-W coating in 3.5% NaCl solution gets improved on heat treatment.