Analysis and interpretation of the micromechanical properties measurements of electrodeposited nickel coatings on different substrates.

Abstract

Fine-grained nickel coatings were electrodeposited by direct current (dc) regime onto different substrates: polycrystalline cold-rolled copper, polycrystalline brass and single crystal (100)-oriented silicon. These composite structures belong to different type of laminated composite systems. The influence of the substrate material and coating plating parameters on microstructural and mechanical properties, such as hardness and adhesion, was characterized by the Vickers microindentation test for different loads. Above critical indentation depth (usually around 10% of the coating thickness), the measured hardness is the so-called “composite hardness”, because the substrate participates in the plastic deformations during indentation. Three composite hardness models (Korsunsky, Chicot-Lesage and Chen-Gao), constructed on different principles, were chosen for fitting the experimental results in order to determine the coating hardness and the critical reduced depth as the adhesion parameter. The coating hardness is mainly influenced by the current density, because increase in current density leads to decrease in grain size and increase in coating hardness. The critical reduced depth as the parameter of adhesion depends on the substrate material.