Electroless deposition of graded Ni–P coatings

In this study, graded Ni–P coatings were deposited on copper substrates by electroless plating method. The surface morphology and cross-section observations were made using scanning electron microscopy and optical microscopy. Degree of crystallinity was determined using X-ray diffraction (XRD). Results showed that the use of electroless Ni–P coatings with gradual change of phosphorus content led to an increase in surface smoothness and the formation of more compact nodules. The XRD patterns indicated that by heat treating, the amorphous phase of the high phosphorus layer was changed to crystalline phases, such as Ni, Ni₂P and Ni₃P. The graded Ni–P coatings had high wear resistance, and the coatings with the sequence of low P/medium P/high P layers from the substrate to the surface had the best wear resistance.