Bioinspired Bouligand structure for the synergistic enhancement of mechanical and thermal properties in 3D-printed C _sf /ZrB ₂ -SiC composites

Short carbon fiber reinforced Ultra-high temperature ceramic matrix composites (Csf/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 Csf/ZrB2-SiC by employing direct ink writing technology. Results indicate that composite with a 30° inter-layer 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 the conventional Csf/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 the short carbon fibers. Hence, the bioinspired Bouligand structure design offers a promising strategy for the synergistic optimization of mechanical and thermal properties in Csf/UHTCMCs.