Laminated structure design for strengthening and toughening of h-BN/ZrB₂–SiC composite ceramics with directional thermal conduction performance

To address the poor mechanical properties of hexagonal boron nitride (h-BN) ceramics while maintaining their high directional thermal conduction performance, this study proposes a laminated structure design using h-BN as the soft, thermally anisotropic matrix layer and ZrB₂–SiC as the hard reinforcing layer. h-BN/ZrB₂–SiC laminated composite ceramics with different layer thickness ratios were fabricated via tape casting and hot-pressing. The h-BN grains maintain strong preferred orientation with their c-axes aligned parallel to the sintering pressure, even after introducing ZrB₂–SiC layers. At an optimal layer thickness ratio of 1:1, the laminated ceramic achieves the best mechanical performance, with a flexural strength of 169.09 ± 18.67 MPa and a fracture toughness of 8.32 ± 0.97 MPa m^1/2, representing increases of 74% and 169%, respectively, compared with tape casted monolithic h-BN ceramics. These enhancements arise from synergistic toughening mechanisms including crack deflection, branching and delamination. Moreover, the laminated structure preserves strong anisotropic thermal conduction. At a layer thickness ratio of 2:1, the composite exhibits the highest thermal conduction anisotropy, with a temperature difference of ∼5 °C between in-plane and through-plane directions at 150 °C. These results demonstrate that the h-BN/ZrB₂–SiC laminated architecture effectively combines high directional heat transfer with significantly improved mechanical properties, offering a promising solution for advanced thermal management in microelectronics and high-power devices.