Surface characteristics of electroless and sputtered Ni–P–W alloy coatings

Ternary Ni–P–W coatings have been fabricated by two kinds of deposition techniques, i.e. electroless plating and RF magnetron sputtering. Surface morphologies and roughnesses of the coatings have been investigated down to nano-scale to probe the relative surface characteristics. Various characterization methods were employed, including scanning electron microscopy (SEM) and atomic force microscopy (AFM). The surface roughness of the electroless platings on a substrate with an Ra value of 2.2 nm were measured to be in the range of tens of nanometers, while that of the sputtered coatings are an order of magnitude less. It was found that the nodular nature of the electroless coatings observed by scanning electron microscopy is responsible for the rougher surface profile as compared to the sputtered coatings. Effects due to various controlling factors, such as additional elements, deposition rate, and thermal history in the heat treatment, are also discussed. After thermal annealing at 400 and 450 °C, there is no appreciable change of surface roughness in both electroless plated and sputtered Ni–P–W coatings.