Synthesis and Tribological Performance of Carbon Nanostructures Formed on AISI 316 Stainless Steel Substrates

Carbon nanostructures were directly grown onto standard AISI 316 stainless steel by spray pyrolysis of α-pinene, a biorenewable material. Two different nanostructures were formed: (1) multi-walled carbon nanotubes when using ferrocene as an external catalyst mixed with α-pinene and (2) ribbon carbon nanofibers when using only α-pinene. In both cases, homogeneous layers of carbon nanostructures randomly distributed and completely covering the metal substrate were observed. Carbon nanotube films were thicker (~230 μm) than carbon nanofiber films (~180 μm). A significant friction reduction was observed for both structures; however, carbon nanofibers displayed a lower friction coefficient (~0.15) than carbon nanotubes (~0.20) at 5 N of load for 200 and 2000 cycles. Scanning electron microscopy and Raman spectroscopy analyses of the wear tracks reveal that, upon rubbing, both carbon nanostructures experienced the removal of stacking faults developing large, parallel and smooth graphene layers with low interfacial shear strength which may account for the friction reduction and wear protection observed.