On the adhesion performance of gradient-structured Ni–P metallic coatings

Hard metallic coatings can provide exceptional protection for industrial settings; however, they usually have a uniform microstructure and suffer from poor adhesion with substrates because of stress/strain incompatibility induced by the sharp interface. Here, a gradient structure that transitions from coarse-grained Ni to nanocrystalline/amorphous Ni–P alloy has been designed to improve the adhesion performance of the electrodeposited Ni–P coatings. Based on two measures of adhesion performance, a high interface shear strength of ∼282.6 MPa and high bending strength of ∼868.4 MPa have been determined for the gradient-structured Ni–P coatings on the CuCrZr alloy substrate, which are increased, respectively, by ∼90% and ∼60% from those of the conventional monolithic-structured Ni–P coating. Post-mortem fractographic analysis reveals that introducing the gradient structure accommodates plastic deformation of the coating and provides exceptional crack arrest capability, contributing to the enhancement of adhesion performances under both shearing and bending. The present work not only reveals how the adhesion performance can be significantly improved in gradient-structured Ni–P coatings, but also provides a promising methodology for manufacturing novel GS metallic coatings with a combination of excellent surface functions and strong interface adhesion.