Self-lubrication behavior of the reaction-formed graphite/SiC composites with optimizing graphite content

Graphite/SiC composites, as one kind of self-lubricating composites, are used in aerospace, aviation and nuclear engineering and other high-tech fields faced with harsh working conditions. The fraction of soft lubricant (graphite) have a significance influence on its lubricating properties. However, it is extremely difficult for the reaction-formed graphite/SiC composites to maintain adequate graphite content given the rapid Si–C reaction at high temperature. In this work, different sizes of composite-powders constructed by graphite and glassy carbon were used as carbon sources to control the carbon content of reaction-formed graphite/SiC composites. The tribological properties of the composites was investigated by a ball-on-disk reciprocating tribometer under different loads, respectively. The results show that the carbon content increased from 15.80 vol% to 38.38 vol% with the increase of powder size (104 μm–345 μm) and the graphite/SiC composites with carbon content of 38.38 vol% exhibited the most outstanding self-lubricating with low friction coefficient (∼0.13) and wear rate (∼10⁻⁶ mm³ N⁻¹m⁻¹). In addition, the wear mechanisms of the composites against steel balls were investigated in detail through the microstructures of the wear surfaces. It reveals that the obtained higher carbon content in the composites can effectively improve the lubricating performance of the composites because of the formation of self-lubricating films derived from more layered structure graphite particles.