Tailoring layer architecture to enhance the toughness of ZrB₂-ZrC-SiC/C laminated ultra-high temperature ceramics

To address the intrinsic brittleness and reliability challenges of Ultra-high temperature ceramics (UHTCs) in thermal protection systems, this study investigates a laminated ceramics architecture (ZrB₂-ZrC-SiC/C) fabricated via tape casting and spark plasma sintering (SPS). The effects of sintering temperature (1600-1900 °C) and structural parameters (layer thickness ratio and interlayer thickness) on the microstructure, mechanical properties, and fracture behavior of the material were systematically investigated. Results indicate that samples sintered at 1800 °C exhibited the highest level of densification and superior overall mechanical properties, achieving a flexural strength of 319 ± 23 MPa and a fracture toughness of 8.41 ± 0.31 MPa m1/2, respectively. By tailoring the layer thickness ratio and interlayer thickness, the crack propagation path and residual stress were effectively controlled. An optimal combination of a 5:1 layer thickness ratio and a 70 μm interlayer thickness yielded a fracture toughness of 10.61 ± 0.45 MPa m1/2, representing an approximately 155% improvement over a monolithic ceramic of the same composition. Microstructural analysis revealed that the laminated architecture significantly enhanced fracture toughness through the carbon (C) interface layers, which promoted repeated crack deflection and extension. This effectively prolonged the crack propagation path and shifted the material toward a non-brittle fracture mode. This study offers a novel approach and an experimental basis for designing ultra-high temperature laminated ceramics that combine high toughness with excellent ablation resistance.