Bioinspired Bouligand structure for the synergistic enhancement of mechanical and thermal properties in 3D-printed C_sf/ZrB₂-SiC composites

Short carbon fiber reinforced ultrahigh temperature ceramic matrix composites (C_sf/UHTCMCs) are recognized as leading candidates for thermal structures owing to their precisely tailorable composition and enhanced tunability in structure and properties. Inspired by nature, the Bouligand structure—characterized by a gradual angular rotation between successive layers—exhibits remarkable load-bearing and thermal conductive capacity. In this study, the Bouligand structure was introduced into C_sf/ZrB₂-SiC by employing direct ink writing technology. The results indicate that the composite with a 30° interlayer Bouligand structure achieves a synergistic improvement in both mechanical performance and thermal diffusion uniformity. Specifically, enhancements of 42% in flexural strength and 35% in fracture toughness were achieved compared to conventional C_sf/ZrB₂-SiC. Meanwhile, the Z-axis thermal conductivity increased by 24.5%, along with a notable enhancement of in-plane thermal diffusion. These improvements can be attributed to the smaller deflection angles and more frequent unidirectional deflections within the 30° Bouligand structure, which promote more pronounced crack deflection. Furthermore, the small-angle rotational design improves in-plane thermal diffusion uniformity by leveraging the high intrinsic radial thermal conductivity of short carbon fibers. Hence, the bioinspired Bouligand structure design offers a promising strategy for the synergistic optimization of mechanical and thermal properties in C_sf/UHTCMCs.