Kun Zhou

SiCf/SiC composites are critical high-temperature materials for aerospace. However, severe machining damage caused by their inherent heterogeneity and brittleness degrades their service life. Currently, low-damage machining methods and quantitative evaluation systems remain insufficient. In this study, typical machining damage such as fiber fracture and interfacial debonding was observed during systematic laser ablation-assisted grinding experiments. Among these damages, the various fracture forms of surface and normal fibers, as well as matrix cracks, were accurately identified by the three algorithms. The YOLO demonstrated the optimal performance, with a recall above 0.91 and a precision of approximately 0.93. Building on this, 22 quantitative indicators were established within the multi-dimensional evaluation system. Specifically, the surface evaluation included per-damage counts and area proportions, as well as the overall degree, whereas the subsurface evaluation included the same metrics, along with entropy and dominance indicators. The mapping relationships between process parameters and damage evolution were revealed. Feed speed was identified as the most dominant process parameter governing damage evolution. Increasing feed speed triggered brittle fiber fractures and macrocracks, with the total number of damage counts rising up 107% and NF-B fractures rising up 230%. Furthermore, multi-objective optimization was performed. Under the optimal parameters, the matrix and the subsurface damage were confined to shallow microcracks, with the damage depth reduced to 4.2 μm. Subsequently, fatigue tests confirmed the optimization's reliability, showing the increased fatigue life resulted from the preserved steady-state frictional energy-dissipation pathway.

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 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.