Preparation and characterization of electroless Ni-P and Ni-P-Si3N4 composite coatings

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 deposits is obtained at a concentration of 10 g/l in the bath. The electroless Ni-P deposits have 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.