Progress and Prospect of Self-Lubrication of SiC Ceramics

Silicon carbide (SiC) has high hardness, low density, and good wear resistance; thus, SiC ceramics are an important tribological material. Under dry sliding conditions, the friction coefficient of SiC ceramics is high (0.4~0.8), reducing the reliability and durability of the tribosystem. Therefore, the widespread application of SiC ceramics is limited. In practical applications, friction components composed of SiC ceramics are sometimes used in special working conditions where lubricants cannot be used, so it is necessary to reduce their friction coefficient by self-lubrication. At present, there are four methods for SiC ceramics to achieve self-lubrication: pre-oxidation, addition of solid lubricant, surface texture, and porous structure. Pre-oxidation and addition of solid lubricant achieve the self-lubrication of SiC ceramics by changing the surface chemical composition, while surface texture and porous structure achieve the self-lubrication of SiC ceramics by changing the surface physical morphology. After pre-oxidation, SiO₂ is formed on the surface of SiC ceramics, which is beneficial to reducing the friction coefficient of SiC ceramics. Although SiC ceramics can achieve self-lubrication after pre-oxidation, the mechanisms of self-lubrication and wear are not yet fully understood. The addition of solid lubricant is to add the material with a layered crystal structure to the SiC ceramic matrix. During the sliding, the solid lubricant is extracted from the SiC ceramic matrix and smears on the friction surface; thus, the solid lubricant can provide a low friction coefficient for SiC ceramics by forming an external lubricating layer. However, the method of adding solid lubricant is not suitable for achieving self-lubrication of SiC ceramics under mild wear conditions. Either surface texture or porous structure is to pre-fabricate concave-convex structure on the surface of SiC ceramics. This concave-convex structure can not only trap wear debris generated during the sliding, reducing plowing and micro-cutting effects, but also decrease the real contact area between SiC ceramics and the counterbody, reducing the adhesion effect. For surface texture, micro-groove or micro-dimple is usually produced by artificial methods, such as laser processing, on the surface of SiC ceramics; when the layer with surface texture on the surface is worn out, it needs to be reprocessed. For porous structure, the pores are formed inside SiC ceramics uniformly; as the surface wears, the internal pores are exposed and continue to function. These methods can achieve self-lubrication of SiC ceramics under certain conditions, leading to a reduction in the energy consumption of the tribosystem. Based on the research results of self-lubrication of SiC ceramics in recent years, this review summarizes the method and mechanism of self-lubrication of SiC ceramics, and prospects the future research directions of self-lubrication of SiC ceramics, in order to provide a basis for the design and investigation of self-lubrication of SiC ceramics.