Surface morphology and structure of electroless ternary NiWP deposits with various W and P contents

Abstract

Electroless ternary NiWP deposits were prepared using an alkaline citrate bath. Sodium tungstate concentration in the bath was varied from 5 to 40 g/L to obtain NiWP deposits containing various W and P contents. Deposits were characterized for their structure, composition, morphology and microhardness. A marginal increase in the grain size (from 1.4 to 3.5 nm) was observed with increasing sodium tungstate content in the bath due to the decrease in phosphorus content in the deposit (from 13 to 4 wt.%). Whereas W content in the deposit was increased (0.5–8.2 wt.%) by the addition of 20 g/L of sodium tungstate in the bath beyond that it was decreased to 4 wt.%. Scanning electron microscopy (SEM) images exhibited the nodular morphology of as-deposited coatings. Deposits were heat treated at various temperatures from 200 to 400 °C for 1 h and phases formed were identified by X-ray diffraction (XRD). Microhardness measurements were made for as-deposited and heat treated coatings at various temperatures. The applicability of the concept of kinetic strength analysis was also validated using the microhardness data obtained as a function of heat treatment temperature.