The material removal mechanism of C_f/SiC composites in brittle regime is more complex than that of single-phase materials. Variable loading nano-scratch tests of unidirectional C_f/SiC composites along different fiber orientations were carried out. According to different fracture mechanism of fibers, the brittle regime of C_f/SiC composites can be subdivided into micro brittle fracture regime and macro brittle fracture regime. In micro brittle fracture regime, cracks were initiated under the extrusion of the indenter, and propagated between the graphite crystallites, resulting in material removal. The scratched surface of fibers was rough. The thickness of fiber subsurface damage layer was the largest when scratching along transverse fibers, and was the smallest when scratching along across fibers. In macro brittle fracture regime, fibers occurred debonding and flexural deformation under the extrusion of the indenter, which caused bending-induced fracture. The scratched surface fluctuated greatly, but the fractures or the surface of fibers were smooth.

C _f / SiC复合材料在脆性状态下的材料去除机理比单相材料复杂。进行了单向C _f / SiC复合材料沿不同纤维取向的可变载荷纳米划痕试验。根据纤维的不同断裂机理，C _f的脆性状态/ SiC复合材料可细分为微脆性断裂状态和宏观脆性断裂状态。在微脆性断裂状态下，裂纹在压头的挤压下引发，并在石墨微晶之间传播，从而导致材料去除。纤维的刮擦表面是粗糙的。当沿横向纤维刮擦时，纤维表面下损伤层的厚度最大，而当沿横向纤维刮擦时，其厚度最小。在宏观脆性断裂状态下，纤维在压头的挤压下发生脱胶和挠曲变形，从而引起弯曲引起的断裂。刮擦表面起伏很大，但断裂或纤维表面光滑。