A low-friction graphene nanoplatelets film from suspension high velocity oxy-fuel thermal spray

The addition of graphene-based nanomaterials is known to improve the tribology properties of materials by lowering the coefficient of friction and reducing wear. The covering of small areas with thin graphene-based films is routinely carried out; however, a fast and efficient way of covering large areas represents an outstanding challenge. Here we present a method for the deposition of graphene nanoplatelets (GNPs) on stainless steel substrates based on suspension high-velocity oxy fuel thermal spray. GNPs were radially injected into the combustion jet, providing sufficient momentum and moderate heat transfer to facilitate effective bonding with the substrate. Upon unlubricated ball-on-disc wear testing against an alumina counterbody, GNPs undergo gradual exfoliation, covering the substrate and thus lowering the friction coefficient (<0.1). We have reported the formation of a thin layer, composed of GNPs having different amounts of disorder, which protects the underlying substrate from wear. GNP structural ordering is studied throughout deposition and wear tests, showing an increase of inter- and intralayer disorder at the nanoscale, whilst largely preserving the GNP microstructure.