Role of humidity in reducing the friction of graphene layers on textured surfaces

A multiple-layer graphene was prepared on steel surface to reduce friction and wear. A graphene-containing ethanol solution was dripped on the steel surface, and several layers of graphene flakes were deposited on the surface after ethanol evaporated. Tribological performance of graphene-contained surface (GCS) was induced by reciprocating ball against plate contact in different RH (0% (dry nitrogen), 30%, 60%, and 90%). Morphology and wear scar were analyzed by OM, 2D profile, SEM, Raman spectroscopy, and XPS. Results show that GCS can substantially reduce the wear and coefficient of friction (COF) in 60% relative humidity (RH). Low COF occurs due to graphene layer providing a small shear stress on the friction interface. Meanwhile, conditions of high RH and textured surface could make the low COF persist for a longer time. High moisture content can stabilize and protect the graphene C-network from damage due to water dissociative chemisorption with carbon dangling bonds, and the textured surface was attributed to release graphene layer stored in the dimple.