Mechanism of low friction coefficient of carbide ceramics and carbon-containing steels

Abstract

To investigate frictional properties of carbide ceramics and carbon-containing steels reciprocating friction experiments were conducted in air. For these experiments, SiC, WC, TiC, and TiCN were used as carbides. Also, Al2O3, Si3N4, TiN, and TiAlN were used as non-carbides. In addition, experiments were conducted using three types of steel as plate materials: JIS SKH4 (carbon content 0.73–0.83%), JIS SUS430 (carbon content lower than 0.12%), and JIS 312L (carbon content lower than 0.02%). As a result of the experiment, a low coefficient of friction was obtained for all combinations of identical carbides. After the friction experiment, the wear debris adhering around the wear scar was analyzed by Raman spectroscopy. As a result, it was found that the wear debris of all carbide ceramics showing a low coefficient of friction contained a graphite-like material. These results demonstrated that a graphite-like material is generated by friction between identical carbide ceramics, as in the case of carbon-based materials such as diamond and DLC. In friction between ceramic balls and steels, the SKH4 plate showed a low coefficient of friction similar to that produced by friction between identical carbides. Raman spectroscopy revealed that the SKH4 plate wear debris contained a large amount of graphite-like materials, while the SUS430 plate wear debris, which showed a high coefficient of friction, contained only a small amount. Moreover, SUS430 showed stronger adhesion to the friction surface than SKH4 did, probably because the graphite-like material generated by friction reduces metal adhesion. These results demonstrated that carbon in steel also produces a graphite-like material by friction, and demonstrated that it lowers the friction coefficient by reducing the shear force and by suppressing adhesion.