Carbon fiber-reinforced ultrahigh-temperature ceramic matrix composites (C_f/UHTCs) suffer from limited structural continuity, regional protection mismatch, and unstable failure mechanisms in oxidative plasma ablation environments above 2500 °C, where single-phase UHTC systems (e.g., HfC or HfB₂) fail to maintain wide-temperature synergistic stability. To address this ablation-limit imbalance, a dual-UHTC-phase C_f–HfC–HfB₂–SiC composite is designed, achieving a wide-temperature synergistic protection effect. The composite exhibits an ultralow linear ablation rate of 1.88×10⁻⁴ mm·s⁻¹ at 2600 °C for 1500 s, increasing only slightly to 2.32×10⁻⁴ mm·s⁻¹ at 2700 °C. Structural analyses reveal a stable triple-layer oxidation architecture consisting of a dense HfO₂ outer layer, an HfO₂–SiO₂ intermediate layer, and a porous inner buffer layer with spatially partitioned responses. First-principles calculations show that the HfC–HfB₂ interface facilitates the formation of a continuous oxygen coordination network, supporting the evolution of a continuous protective oxide scale. These findings suggest a zonal synergistic protection behavior associated with the cooperative evolution of different ablation regions under nonuniform ultrahigh-temperature environments.

With the advancement of hypersonic vehicles, extreme high temperature environments have imposed increasingly stringent requirements on the performance of thermal protection systems. Consequently, the development of high-performance thermal protection materials capable of withstanding extreme conditions has become a primary focus of current research. Ultra-high temperature ceramics (UHTCs) and their composites, known for their excellent oxidation resistance and ablation performance, are regarded as highly promising non-ablative thermal protection materials. This paper provides a systematic review of recent research progress on UHTC composites in several key areas, including innovations and optimizations in fabrication processes, exploration of toughening strategies and mechanisms, in-depth studies on oxidation and ablation resistance mechanisms, and the development and potential applications of high-entropy ceramics. Furthermore, the paper discusses the practical application prospects of UHTCs and their composites in extreme environments, analyzes the current technical challenges, and proposes future research directions and priorities.

Carbide- and boride-based ultrahigh temperature ceramics (UHTCs) are the materials of choice for hypersonic vehicles and scramjet engines. Nevertheless, these UHTCs are prone to oxidation in an oxygen-containing atmosphere. In addition, the high density of these UHTCs limits their widespread applications in the aerospace industry. To address the urgent need for lightweight thermal protection materials (TPMs) and mitigate oxidation-induced volume changes, a novel HfO₂–SiBOC ceramic was designed in this work, in which amorphous SiBOC is the matrix, while nanosized HfO₂ acts as the reinforcement phase. The advantages of these HfO₂–SiBOC ceramics are as follows. This HfO₂–SiBOC ceramic simultaneously achieves light weight by tuning the SiBOC matrix content and mitigates oxidation through nanosized HfO₂ uniformly dispersed in the matrix via preferential oxidation of Hf from the precursor. To achieve the above goals, a novel amber liquid SiHfBOC precursor was synthesized via a sol–gel and solvothermal method as the first step. The precursor, featuring Si–O–Si, Si–O–B main chains and Si–O–Hf side chains, achieves a high ceramic yield of 80.8 wt%. Its polymerization mechanism and properties were studied. The effects of the Hf/Si ratio and pyrolysis temperature on the SiHfBOC ceramic powder composition, microstructure evolution behavior, and oxidation resistance were systematically investigated. Based on the above results, HfO₂–SiBOC bulk ceramics were then prepared by hot pressing sintered powders. Oxyacetylene flame ablation tests at 2000 °C for 300 s confirmed their near-nonablation behavior, demonstrating exceptional ablation resistance. The ablation mechanism is elucidated. This work provides a new strategy for designing lightweight high-performance polymer-derived ceramics (PDCs) for ultrahigh temperature applications.

To meet the stringent demands for toughening and ablation resistance in high-speed aircraft components, C/C-SiHfCB composites were fabricated by introducing a novel liquid SiHfCB precursor into a porous C/C matrix via high-pressure precursor infiltration and pyrolysis. This approach yielded an integrated three-dimensional continuous ceramic phase tightly bonded to the matrix. The composite achieved a flexural strength of 237 ± 42 MPa with non-brittle fracture, a critical thermal shock temperature difference of 912℃. During oxyacetylene flame tests, extremely low linear ablation rates of 5.7 × 10⁻⁴ mm/s and 15.6 × 10⁻⁴ mm/s were recorded at 2000℃ and 2150℃, respectively. An effective oxygen diffusion barrier consisting of an HfO₂ skeleton with SiO₂-filled pores was formed. This study offers a viable strategy for the synergistic optimization of mechanical and ablation properties.

Aerodynamic heating, oxidation, ablation, and high dynamic pressure represent the extreme environments that aerospace vehicles must withstand during high-Mach atmospheric or trans-atmospheric flight. The temperature of critical components on the vehicles can reach 3000 °C or higher. Such an extreme environment imposes stringent requirements on thermal protection materials, such as ultrahigh temperature ceramics (UHTCs) and their composites. The formation of a dense oxide scale with low oxygen permeability is crucial for ensuring the ablation resistance of UHTCs. As such, searching for oxides with melting points exceeding 3000 °C is one of the emerging directions. This perspective aims to briefly review the development of UHTCs and their composites over the past few decades. In addition, promising directions are proposed to meet extreme environments. Concurrently, the assistance of multiscale modeling techniques to accelerate the development and application of UHTCs and their composites is emphasized.

Oxide scales grown on carbides or borides based ultrahigh thermal protection materials during service play crucial roles in the safe operation of the systems in extreme environments, where advancing technologies are pushing temperature limits beyond 3000 °C, exceeding the melting points of all known nonradioactive oxides. Although cationic solid solutions offer a pathway to modulate melting behavior, conventional phase diagrams show that most solid solutions exhibit lower melting points than their parent components. The mechanisms underlying melting point elevation in oxides have remained unclear. Here, we demonstrate a cationic design strategy for ultrahigh melting point oxides based on simultaneous control of the valence electron concentration, cation size, orbital overlap, coordination number and crystallographic symmetry. Using this approach, we developed a Ta-doped HfO₂ solid solution with a melting point of 3006 °C, the highest reported nonradioactive oxide, which represents an increase of nearly 150 °C over the parent oxide. This approach should be universally applicable to designing various ceramics with high or ultrahigh melting points.

The difficulty of reducing the diameter of lutetium oxide (Lu₂O₃) continuous fibers below 50 μm not only limits the flexibility of the sample but also seriously affects their application and development in high-energy lasers. In this work, a Lu-containing precursor with high ceramic yield was used as raw material, fiberized into precursor fibers by dry spinning. The pressure-assisted water vapor pretreatment (PAWVT) method was creatively proposed, and the effect of pretreatment temperature on the ceramization behavior of the precursor fibers was studied. By regulating the decomposition behavior of organic components in the precursor, the problem of fiber pulverization during heat treatment was effectively solved, and the Lu₂O₃ continuous fibers with a diameter of 40 μm were obtained. Compared with the current reported results, the diameter was reduced by about 50%, successfully breaking through the diameter limitation of Lu₂O₃ continuous fibers. In addition, the tensile strength, elastic modulus, flexibility, and temperature resistance of Lu₂O₃ continuous fibers were researched for the first time. The tensile strength and elastic modulus of Lu₂O₃ continuous fibers were 373.23 MPa and 31.55 GPa, respectively. The as-obtained flexible Lu₂O₃ continuous fibers with a limit radius of curvature of 3.5–4.5 mm had a temperature resistance of not lower than 1300 ℃, which established a solid foundation for the expansion of their application form in the field of high-energy lasers.

Ultra-high temperature ceramics (UHTCs) are generally referred to the carbides, nitrides, and borides of the transition metals, with the Group IVB compounds (Zr & Hf) and TaC as the main focus. The UHTCs are endowed with ultra-high melting points, excellent mechanical properties, and ablation resistance at elevated temperatures. These unique combinations of properties make them promising materials for extremely environmental structural applications in rocket and hypersonic vehicles, particularly nozzles, leading edges, and engine components, etc. In addition to bulk UHTCs, UHTC coatings and fiber reinforced UHTC composites are extensively developed and applied to avoid the intrinsic brittleness and poor thermal shock resistance of bulk ceramics. Recently, high- entropy UHTCs are developed rapidly and attract a lot of attention as an emerging direction for ultra-high temperature materials. This review presents the state of the art of processing approaches, microstructure design and properties of UHTCs from bulk materials to composites and coatings, as well as the future directions.