Novel suspension route to incorporate graphene nano-platelets in HVAF-sprayed Cr3C2-NiCr coatings for superior wear performance

Journal article, 2021

Graphene nano platelets (GNP) have several attractive properties, including excellent lubricity that can be used to develop wear-resistant coatings. Thermally sprayed chromium carbide-nickel chromium (Cr3C2-NiCr) coatings are widely employed to impart wear resistance to engineering components. This work attempts to improve the wear resistance of high velocity air fuel (HVAF) sprayed Cr3C2-NiCr coatings by incorporating GNP using a hybrid approach in which Cr3C2-NiCr (powder) and GNP (suspension) are co-axially injected. Two different powder-to-suspension delivery ratios were employed in this study that utilizes a liquid feedstock in tandem with a HVAF system. Furthermore, for comparison, a pure (without graphene) Cr3C2-NiCr reference coating was deposited by the HVAF process using identical spray parameters. The as-sprayed coatings were characterized for their microstructure and phase constitution by SEM/EDS and X-Ray Diffraction. Mechanical properties such as hardness and fracture toughness were evaluated using micro-indentation technique. The hybrid coatings were subjected to dry sliding wear tests and wear performance was compared with reference Cr3C2-NiCr. The GNP incorporated hybrid coatings exhibited lower CoF and lower wear rates than the reference Cr3C2-NiCr coating. Post wear SEM/EDS analysis revealed different wear mechanisms predominant in the investigated coatings. Utilizing the above as a case study, this work provides key insights into a new approach to produce GNP incorporated coatings for mitigating wear.