Low-Friction Characteristics of Nanostructured Surfaces on Silicon Carbide for Water-Lubricated Seals

This paper experimentally investigates the effects of induced nanostructures on the reduction of friction for mechanical seals. This study examines the properties of low-friction seals, whose surfaces were fabricated using a titanium-sapphire-based femtosecond laser in the authors' previous study. Tribological experiments are carried out with a ring-on-disk apparatus under various loads, which are increased in a stepwise manner. Three surface patterns on seals are used for tribological investigations: a flat surface, a step-bearing surface, and a step-bearing surface combined with nanostructures. The experimental results show that the step-bearing surface with nanostructures had the smallest friction coefficient, which was about 20 % smaller than that of the step-bearing surface without nanostructures. Nanostructures on the SiC surface generate a thicker SiO2 film than that on SiC without nanostructures and prevent the direct contact of the relative moving surfaces of the ring and disk when the water film breaks down. This study also examines the surface damage of the specimens. Scanning electron microscopy images indicate that the nanostructures on the specimen are not damaged with a step-bearing surface under the hydrodynamic lubrication condition. Hence, employing nanostructures on the surfaces of mechanical seals has great potential to reduce the friction coefficient.