Nanocontact Characteristics of Composite Galvanic Chrome Coatings Detected by Sclerometry and Atomic Force Microscopy

Abstract

Using the atomic force microscopy (AFM) and scanning electron microscopy (SEM) the surface morphology of chromium coatings formed from standard electrolytic chromium plating with additional 10-120 mg/l of multi-walled carbon nanotubes (MWCNT) was investigated. Methods of sclerometry (or scratch testing) and AFM were used to study the dependence of the nanocontact characteristics of composite electrochemical chromium coatings on the concentration of CNTs in the electrolyte. With a CNT concentration of 60-70 mg/dm 3 in the electrolyte, the hardness of the Cr/MWCNT coatings increased up to 65 %, the volume of material displaced by scratching decreased to 55 % with respect to pure electrolytic chromium. Improvement of the nanocontact characteristics of composites can be associated with a decrease in the average grain size and a change in the morphology of the coating surface. Using the example of composite chrome coatings, it is shown that the sclerometry method is more sensitive and representative for description of physical-mechanical properties of composite electrolytic coatings, including those with a high surface roughness (Ra ≈ 1.5-2 μm) than micro-and nanoindentation methods.