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 ZrO 2 sol into conventional electroless Ni–P plating bath. Ni–P–ZrO 2 nano-composite coatings have been produced with highly dispersive ZrO 2 nano-particles inside the alloy coating matrix. The as plated nano-composite coating exhibits much increased microhardness up to 1045 HV 200 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 ZrO 2 sol is introduced into the coating. By comparison with the plain Ni–P coating and conventional Ni–P–ZrO 2 composite coating incorporated with solid ZrO 2 powders, two mechanisms for the increased mechanical properties are proposed based on nano-particle dispersion strengthening and phase transformation strengthening. The formation mechanism of ZrO 2 nano-particle is also discussed.