Preparation and Characterization of Electroless Ni-P and Ni-P-Si₃N₄ Composite Coatings

SUMMARY

The present work pertains to the study of electroless Ni-P and Ni-P-Si₃N₄ composite coatings. The deposits are obtained from a proprietary high phosphorus electroless nickel plating bath, comprising nickel sulphate, sodium hypophosphite, complexing agents and stabilizers. The maximum weight percent of Si₃N₄ incorporated in the electroless deposit is obtained at a concentration of 10 g/l in the bath. The electroless Ni-P deposits having 0%, 2.01%, 5.81% and 8.10% of Si₃N₄, respectively, obtained from baths containing 0, 2, 5 and 10 g/l of Si₃N₄, are characterized by optical microscopy, XRD and TEM. Hardness is found to increase with the incorporation of Si₃N₄ at all heat treatment temperatures studied. Also hardness increases with an increase in weight percent of Si₃N₄ incorporated in the deposit. The analyses of the composite coatings by XRD and TEM reveal that the inclusion of Si₃N₄ particles does not change the amorphous nature of the Ni-P matrix.