Wear characteristics of functionally graded nanocrystalline Ni–P coatings

Abstract

In this study, functionally graded Ni–P coatings with a gradual change of phosphorus content were deposited using a single electroless bath. For comparing tribological and mechanical properties, three types of single layer coatings were deposited. According to the results among the single layer coatings, medium P coating had the minimum wear resistance, while its hardness was not minimum. The main reason may be that the medium P coating had the minimum H/E ratio, and this ratio is a more appropriate parameter than hardness for predicting wear resistance. Results of nanoindentation test showed gradual changes in hardness profile in the cross-section of FGCs due to the gradual changes of phosphorus content in the thickness of the coatings and, consequently, gradual changes in structures. In addition, functionally graded coatings indicated much better wear resistance than single layer coatings because during the wear process cracks were effectively prevented through the thickness as a result of gradual composition and structures.