Fabrication and characterization of electroless Ni–P–ZrO₂ nano-composite coatings

A novel technique has been developed to produce nano-particle oxide reinforced metal coatings. This method is based on electroless deposition process by adding ZrO₂ sol into conventional electroless Ni–P plating bath. Ni–P–ZrO₂ nano-composite coatings have been produced with highly dispersive ZrO₂ nano-particles inside the alloy coating matrix. The as plated nano-composite coating exhibits much increased microhardness up to 1045 HV₂₀₀ and remarkably improved wear resistance. X-ray and electron diffraction patterns show a phase transformation in the Ni matrix of the coating from amorphous to nanocrystalline when ZrO₂ sol is introduced into the coating. By comparison with the plain Ni–P coating and conventional Ni–P–ZrO₂ composite coating incorporated with solid ZrO₂ powders, two mechanisms for the increased mechanical properties are proposed based on nano-particle dispersion strengthening and phase transformation strengthening. The formation mechanism of ZrO₂ nano-particle is also discussed.