ZrB2-Based "Brick-and-Mortar" Composites Achieving the Synergy of Superior Damage Tolerance and Ablation Resistance.

The intrinsic brittleness and poor damage tolerance of ultrahigh-temperature ceramics are the key obstacles to their engineering applications as nonablative thermal protection materials. Biomimetic layered or "brick-and-mortar" hybrid composites composed of alternative strong/weak interfaces exhibit excellent strength and high toughness; however, the commonly used interfacial materials are weak and have poor thermal stability and ablation resistance, which strictly limit their use in high-temperature and oxidative environments. In this work, ZrB2-based "brick-and-mortar" hybrid ceramics were constructed with a hierarchical biomimetic design to improve the fracture resistance and damage tolerance. ZrB2-20vol %SiC ceramics containing 30 vol % reduced graphene oxide nanosheets were used as the weak interface to increase crack growth resistance without destroying the excellent ablation resistance. Finally, the ZrB2-based "brick-and-mortar" composites achieve the synergy of superior damage tolerance and ablation resistance.

Ordered Silica Nanoparticles Grown on a Three-Dimensional Carbon Fiber Architecture Substrate with Siliconborocarbonitride Ceramic as a Thermal Barrier Coating.

Hierarchical structure consisting of ordered silica nanoparticles grown onto carbon fiber (CF) has been fabricated to improve the interfacial properties between the CFs and polymer matrix. To improve the reactivity of CFs, their surface was modified using poly(1,4-phenylene diisocyanate) (PPDI) via in situ polymerization, which also resulted in the distribution of numerous isocyanate groups on the surface of CFs. Silica nanoparticles were modified on the interface of CF-PPDI by chemical grafting method. The microstructure, chemical composition, and interfacial properties of CFs with ordered silica nanoparticles were comprehensively investigated by scanning electron microscopy, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy. Results indicated an obvious increase in the interfacial shear strength, compared to that of CF precursor, which was attributed to silica nanoparticles interacting with the epoxy resin. Furthermore, siliconborocarbonitride (SiBCN) ceramic was used as thermal barrier coating to enhance 3D CF architecture substrate antioxidant and ablation properties. Thermogravimetric results show that the thermal stability of the CF with SiBCN ceramic layer has a marked increase at high temperature.