Optimizing the Tribological Behavior of Nanocrystalline Inconel 718 by Solid Lubricant Reinforcements

Bulk metal matrix composites of nanocrystalline Inconel 718 (IN718) reinforced with various solid lubricant (SL) particles were fabricated from powder blends using a combination of colloidal mixing and high-pressure torsion (HPT). Conventional (MoS 2 , WS 2 , graphite) and modern SL (graphene nanoplatelets and functionalized carbon nanotubes) were incorporated at varying concentrations. Tribological performance was investigated under ambient conditions with a focus on running-in behavior. Linear reciprocating ball-on-disc tests were conducted against spherical Si 3 N 4 and 100Cr6 counterbodies, with wear characterized by confocal laser microscopy and scanning electron microscopy, including qualitative chemical analysis. The friction evolution of HPT-deformed IN718 exhibited strain-dependent behavior, as evidenced by microhardness measurements. Conventional SL and graphene provided predominantly limited improvements in friction and wear. Only carbon nanotube reinforcements consistently improved tribological performance across all concentrations and counterbody materials. Best results were achieved at a content of 5 wt%, exhibiting stable self-lubricating behavior, thereby reducing the friction coefficient from 0.78 to 0.14 and the specific wear rate by an order of magnitude to ~ 10 –9 mm 3 N −1 mm −1 . These findings highlight the potential of carbon nanotube-reinforced IN718 composites for more sustainable tribological applications under ambient conditions.