High-temperature evolution of specialty ceramic fibers and novel toughening mechanism via bio-inspired conchoidal-like architectures

The development of high-temperature wave-transparent ceramic fibers represents a critical breakthrough in overcoming material limitations for advanced radome applications. This investigation systematically elucidates the high-temperature structural evolution mechanisms of boron nitride (BN) and alumina (Al₂O₃) fibers, with particular emphasis on the first discovery of biomimetic conchoidal-like layered architecture in BN fibers demonstrating multiscale toughening mechanisms. The hierarchical structure consists of hexagonal BN grains aligned along the fiber axis, which are interlocked to form an intricate three-dimensional network. Under mechanical stress, this architecture exhibits multi-level coordinated responses: Lamellar grain boundary sliding induces crack deflection along intercrystalline paths, and non-close-packed BN grains undergo stress-induced rotation to dissipate energy. These synergistic mechanisms collectively sustain fiber pull-out effects. Benefiting from the thermal stability of covalent B–N bonds coupled with continuous energy dissipation through 2D boundary sliding, the bending strength retention rate of BN fibers after sintering at 1400 °C is 57.67 % relative to their bending strength at room temperature, whereas for Al₂O₃ fibers, the bending strength retention rate after sintering at 1400 °C is only 7.26 % compared to their room-temperature value. Following sintering at 1400 °C, the bending strength retention rate of BN fibers exhibits a 794 % enhancement compared to that of Al₂O₃ fibers. This study establishes the decisive role of biomimetic layered structures in regulating high-temperature ceramic fiber performance, providing groundbreaking theoretical foundation for designing next-generation wave-transparent materials in strategic domains including aerospace defense systems and satellite communication technologies.