Suspension High Velocity Oxy Fuel (SHVOF) Thermal Spraying of Cr2O3 with Graphene Nanoplatelets for Dry Sliding Wear Protection

Thermally sprayed Cr₂O₃ coatings have been shown to provide excellent protection against wear in many engineering applications. These coatings are traditionally applied using air plasma spray technology; however, suspension high velocity oxy fuel thermal spraying (SHVOF) is a promising method to improve coating properties as this technique enables powder feedstocks too small to be processed by mechanical feeders to be sprayed, allowing the production of coatings with improved density and mechanical properties. Furthermore, the addition of graphene nanoplatelets (GNPs) to the liquid feedstock has been shown to improve the mechanical properties of SHVOF sprayed ceramic coatings (e.g., alumina). In this study, an aqueous based nanometric Cr₂O₃ suspension and a Cr₂O₃ suspension with 1 wt.% GNP, prepared via a proprietary process, were sprayed by a SHVOF thermal spray onto 304 stainless steel substrates. The microstructure of Cr₂O₃ and Cr₂O₃+ GNP coatings was analysed using SEM and XRD alongside microhardness, fracture toughness and porosity investigations. Dry sliding wear performance was investigated using a micro tribometer against an alpha alumina ball at a load of 10 N. The significantly improved wear performance of the nanocomposite coatings was rationalised due to its unique microstructure and improved mechanical properties.