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

Abstract

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.