Self-driven bidirectional redistribution of Zr species constructing a dual oxidation barrier in SiC-ZrC ultrafine fibers

Silicon carbide (SiC) ultrafine fibers hold great promise for flexible thermal protection systems, yet their service temperature is severely limited by oxidative degradation above 1300 °C. Herein, SiC-ZrC ultrafine fibers (SZF) with linearly tunable Zr content are fabricated by electrospinning, electron-beam curing, and carbothermal pyrolysis. The optimal SZF-20 maintains structural integrity after oxidation at 1600 °C for 30 min and at 1300 °C for 30 h in air. Focused ion beam sectioning and transmission electron microscope reveal temperature-dependent spatial redistribution of Zr species across the oxide scale. During high-temperature oxidation, nonstoichiometric ZrO x C y intermediates redistribute inward along the advancing oxidation front and accumulate at the oxide-matrix interface, forming a linear, high-melting-point inner ZrO 2 barrier. Meanwhile, some ZrO 2 grains segregate outward as the SiO 2 matrix crystallizes into cristobalite, pinning grain boundaries to create an outer passivation layer. This dual-barrier architecture synergistically suppresses oxygen ingress and microcrack formation, thereby enabling reliable short-term high-temperature oxidation tolerance up to 1600 °C. The assembled fiber aerogels demonstrate nearly full shape recovery with residual strain below 1% following 80% compression, good thermal shock stability over repeated rapid cycles between 1600 and 25 °C, and low thermal conductivity, highlighting their great potential as reusable high-temperature thermal protection materials.