Nanomechanical properties of functionally graded composite coatings: Electrodeposited nickel dispersions containing silicon micro- and nanoparticles

Abstract

Functionally graded composite coatings constitute a class of materials which are mostly used for mechanical and tribological applications. Among these materials, nickel metal deposits with incorporation of SiC particles have excellent mechanical properties due to nickel metal and good tribological properties due to the SiC particles. In this work, nickel coatings containing different sizes of SiC particles, nanoparticles and microparticles (10 nm to 5 μm), were electrodeposited from an additive-free sulfate bath containing nickel ions and SiC particles. The material properties of the coatings were compared to nickel coatings containing microparticles (5 μm). The effect of current density, SiC content in the bath, and electroactive species concentration on the codeposition of SiC were studied. Afterwards, the effect of particle size and codeposition percentage of SiC particles on the nanomechanical properties on the morphology and structure of the electrodeposits were investigated. The coatings were analyzed with scanning electron microscopy (SEM), X-ray diffraction (XRD), nanoidentation and lateral force microscopy (LFM). The Ni–SiC electrocomposites, prepared at optimum conditions, exhibited improved nanomechanical properties in comparison to pure nickel electrodeposits. The improved properties of the composite coatings are associated to structural modifications of the nickel crystallites as well as the morphology of the electrodeposited layers. The improved nanomechanical properties of electrocomposites containing nanosized SiC particles, as compared to electrocomposites containing micron-sized SiC particles, is attributed to the increasing values of the density of embedded SiC particles with decreasing particle size and the mechanism of embedment of the SiC particles.