Process–structure–property coupling in vat-photopolymerized Si/SiC composites through PRIP-driven SiC formation and morphology-retained transformation of SiC whiskers

In this work, a morphology-retained transformation of SiC whiskers into fibrous Si during reactive melt infiltration is reported for the first time. Silicon carbide (SiC) offers high specific strength and stiffness; however, conventional processing routes still face challenges in fabricating lightweight components with complex geometries. Vat photopolymerization (VPP) combined with reactive melt infiltration (RMI) provides an effective route for producing architected SiC-based composites, although the roles of residual-Si morphology and distribution in determining mechanical performance remain insufficiently understood. This work demonstrates that SiC whiskers undergo a morphology-retained interfacial transformation during reactive melt infiltration, which contributes to enhanced fracture toughness. In this work, a Si-morphology regulation strategy based on SiC whiskers, together with phenolic resin infiltration and pyrolysis (PRIP), was developed to improve the mechanical properties of Si/SiC composites fabricated by VPP and RMI. During RMI, SiC whiskers undergo localized interfacial dissolution in molten Si, and the original whisker-shaped channels are subsequently occupied by residual Si after infiltration and cooling, forming whisker-like residual-Si regions. Meanwhile, PRIP introduces additional carbon into the porous preforms, which reacts with molten Si to form additional fine SiC and reduces the amount and continuity of residual Si. These two microstructural regulation mechanisms jointly promote crack deflection, branching, and crack-path tortuosity, thereby enhancing fracture toughness. The fabricated Si/SiC composites achieved a maximum bulk density of 3.02 g/cm³ , a maximum flexural strength of 436.27 ± 9.57 MPa, and a maximum fracture toughness of 5.02 ± 0.06 MPa·m 1/2 . Compared with samples without Si-morphology regulation and PRIP treatment, the maximum flexural strength and fracture toughness increased by 31.70% and 36.78%, respectively. In addition, the composites containing 5 vol% SiC whiskers exhibited minimal anisotropic shrinkage during pyrolysis, with shrinkages of 0.81 ± 0.28%, 2.67 ± 0.25%, and 4.18 ± 0.38% in the X, Y, and Z directions, respectively, which is beneficial for high-precision near-net-shape fabrication. These results provide a practical route for manufacturing high-precision, complex-shaped Si/SiC composites with improved strength and toughness.