Preparation of Electroless Ni-P Composite Coating and its Tribological Properties

Abstract

The Ni-P composite coatings onto 4043 aluminum alloy were prepared by electroless plating with nickel sulfate and sodium hypoposphite as raw material. The Ni-P composite coatings were heat-treated for 1 hour at 200°C, 300°C, 400°C, 500°C and 600°C, respectively. The tribological behaviour of the coatings was investigated on a vertical universal friction/wear tester under dry friction. The morphology and phase structure of the composite coatings were characterized by scanning electron microscope (SEM) and transmission electron microscope (TEM), and the microhardness of the composite coatings were measured by Vickers diamond indenter. The results showed that the as-deposited coatings had smooth cellular pattern and amorphous structure, and the microhardness of the coatings reached the maximum at 400°C heat treatment, the reason is the formation of Ni3P alloy phase with increasing of the heat treatment temperature. The friction coefficient of coatings annealed at 400°C is the lowest. The wear loss was found to increase with corresponding increase in load and sliding speed. It was found that the wear mechanism of the as-deposited Ni-P composite coatings was dominated by adhesive wear and scuffing under the experimental conditions, but the wear mechanism of the coatings annealed at 400°C was scuffing.