The critical role of machining-induced damages in tribological and wear behavior of C_f/SiC composite

C_f/SiC composite is regarded as promising frictional materials for advanced high-speed railway and civil aircraft. Severe damages can occur in C_f/SiC composite during mechanical machining; however, their potential impact on the friction performances is unclear. This study conducted comparative reciprocating friction tests using ground and unprocessed C_f/SiC composite, and clarified the role of grinding-induced damages in tribological and wear behavior. It was revealed that the coefficient of friction (COF) gradually decreased and then remained stable around 0.38 during friction; various fracture damages, including fiber fracture and pulling-out, matrix cracking, and interface debonding, were observed in C_f/SiC composite after grinding, resulting in a higher COF (0.73) but shorter decreasing period compared with unprocessed materials. These damages were removed with the continuous wear of surface materials, and a friction film with oxides was rapidly formed due to the micro wear debris adhering, which played the role of lubrication and antifriction. Furthermore, the wear mechanism of C_f/SiC composite underwent a transition from abrasive wear to attrition wear and adhesion wear during the entire friction process, and the existence of grinding-induced damages significantly accelerated the transition.