To mitigate the formation of a porous oxide layer in a single HfC coating during long-term ablation, this work employed chemical vapor deposition to fabricate solid-solution HfxZr1-xC coatings on SiC-coated C/C composites. The microstructure, thermal properties, and ablation behavior of these coatings were investigated through experimental and first-principles calculations. Results indicated that all coatings exhibit a single-phase NaCl-type solid solution structure with uniform elemental distribution. As the Zr content increases, the coefficient of thermal expansion of the HfxZr1-xC coating increases, while the enhanced lattice distortion leads to reduced thermal conductivity. After proportional regulation, the mass and linear ablation rates of the Hf0.5Zr0.5C coating are reduced by 40.98 % and 46.15 %, respectively, after ablation for 180 s at 2300 degrees C. The formation of a dense and uniform Hf0.5Zr0.5O2 solid-solution oxide layer enhances the ablation resistance, which is attributed to its compositional homogeneity and the fusion of grain boundaries during ablation, thereby effectively suppressing oxygen diffusion and promoting more cooperative oxygen transport. This study indicates that solid-solution structure ceramic coatings hold promising prospects for application in the field of ultra-high-temperature thermal protection. (c) 2026 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

Ultra-high temperature thermal protective materials (UHTPMs), endowed with exceptional temperature resistance, high mechanical strength, and superior corrosion resistance, have emerged as critical materials in fields of aerospace, nuclear energy, and advanced equipment manufacturing. Recently, driven by the dual impetus of the worsening global energy crisis and the continuous advancement of aircraft performance, UHTPMs are gradually evolving toward lightweight and long service life. Conventional materials have been increasingly unable to meet the current stringent demands, making the upgrading of material systems an urgent necessity. The intrinsic properties of UHTPMs are core indicators that directly measure their service stability and reliability. Advanced characterization technologies serve as the key to material screening. Moreover, the correlation between “composition-structure-process-property” will be essentially established only by systematic elucidation of their thermal protective mechanisms. Therefore, this review highlights the recent progress in advanced characterization techniques and investigation methodologies for thermal protective mechanisms of UHTPMs, aiming to provide theoretical guidance and technical references for the development of new high-performance UHTPMs.

Hafnium carbonitride (HfCxN1−x) ceramics show great potential for thermal protection systems due to their ultra-high melting point, and investigating their ablation behavior is essential for their application under extreme conditions. In this work, HfCxN1−x ceramics with varying nitrogen contents were synthesized via polymer-derived ceramic followed by spark plasma sintering. Laser ablation tests showed that HfC0.75N0.25 achieved excellent ablation resistance under the laser power of 500 W, with linear and mass ablation rates of 1.08 µm s−1 and 0.32 mg s−1, respectively. This is ascribed to the high melting point and exceptional thermal stability of HfC0.75N0.25, which result from moderate nitrogen incorporation. During laser ablation, dislocation accumulation and the formation of lath-like structures dissipate part of the laser heat flux. Subsequently, a dense Hf(C, N, O) solid solution layer with high viscosity forms, which effectively impedes oxygen diffusion and maintains stable ablation resistance of HfC0.75N0.25. Conversely, excessive nitrogen incorporation induces the formation of the Hf7O8N4 phase with numerous defects and crack nucleation, ultimately deteriorating laser ablation resistance. These findings provide useful insights for the design and development of ultra-high temperature ceramics for applications in extreme environments.

The high-temperature oxidation of Carbon/carbon (C/C) composites limits their application as hot-end structural materials in the aerospace industry. To solve this problem, a HfSiO4-based coating with strong oxygen blocking ability on the C/C composites was fabricated by a compound method of slurry brushing and in-situ oxidation sintering. The C/C composites were protected by the coating for 2257 h at 1773 K, 121 h at 1973 K in air, with a mass loss of about 0.50 wt%, respectively. Such good performance was attributed to the Hf-Si-O oxygen barrier layer with abundant and uniformly distributed HfSiO4 particles (Volume accounting for over 65 %). The HfSiO4 particles could reduce the volatile mass of the SiO2 glass, and relieve the difference of coefficient of thermal expansion (CTE) between the SiC inner coating and SiO2 in the outer coating. More importantly, the oxygen diffusion resistance of the Hf-Si-O layer with HfSiO4 as the main phase was significantly enhanced, providing a basis for optimizing the composition of oxidation resistance coatings at 1973 K and above in air.

Despite the improved ablation resistance offered by Hf-based ultra-high temperature ceramics (UHTCs) in carbon/carbon (C/C) composites, the porous oxide scales formed during ablation limits their long-term thermal stability, hindering advanced application. Herein, this work proposed the incorporation of Hf/Ti+Ta with varying molar ratios into C/C composites via reactive melt infiltration, and the resulting multi-component oxides after ablation promoted the formation of a dense oxide layer, thereby improving long-term ablation performance. The finding reveals that all samples were relatively dense and exhibited an identical layered structure around carbon fibers. Notably, the composites with a Hf/Ti/Ta molar ratio of 8:2:1 (8-HTT) exhibited superior ablation resistance, owing to the formation of a dense, adherent surface oxide layer, consisting of (Hf, Ti, Ta)O2 and HfTiO4. As the ablation duration increased to 240 s, the linear ablation rate for 8-HTT decreased to 0.7 mu m/s, which was attributed to the self-healing effect enabled by low-melting-point oxide Hf6Ta2O17. This work establishes a theoretical foundation and optimization strategy for designing high-performance ablation-resistant C/ C composites for extreme thermal environments.

Composite materials with gradient structures are ideal candidates for high-temperature thermal protection systems of aerospace vehicles due to their unique properties within distinct regions. Herein, we report a novel method of localized filtrating modification (LFM) for fabricating gradient materials, offering a lightweight design and exceptional thermal protection performance. Notably, the gradient structure results in a density reduction of 37 % and a linear ablation rate of only 1.43 mu m s(-1) after 120 s ablation, which is 75 % lower than that of uniform composites attributed to the reduced heat accumulation at the ablation center. Additionally, the particle refinement by LFM and the self-healing effect of the oxides of (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C prevent the failure of the produced oxide barrier layer. In this work, lightweight gradient composites that can withstand elevated temperatures with excellent thermophysical properties and ablation resistance are developed, providing a universal and adaptable strategy for the design and fabrication of advanced functional gradient materials.

The protective efficacy of hafnium carbide (HfC) coatings on Carbon/Carbon (C/C) composites is closely linked to the dynamic evolution of their oxide layer during ablation. While the dense hafnium oxycarbide (HfC1-xOx) acts as an effective barrier, its further oxidation into the loose HfO2 leads to the degradation of the protective performance of the coatings. This study extends a composition-evolution ablation model by explicitly resolving surface topography to investigate the spatiotemporal evolution of the heterogeneous oxide layer and the protective performance during ablation. The proposed ablation model is validated against experimental measurements of elemental (C, O, and Hf) distributions after ablation. The results reveal a two-stage ablation mechanism: an initial protective stage maintained by the growth of dense HfC1-xOx, followed by an accelerated degradation stage triggered by the accumulation of porous HfO2. This study also demonstrates that the geometric effect leads to a concentrated oxygen flux in the valley regions, resulting in a more rapid consumption of HfC compared to the peak regions. Furthermore, an elevated oxygen mole fraction (from 20% to 60%) accelerates the degradation of the oxygen barrier properties, causing an approximately 11% reduction in its optimal performance. These insights provide a basis for the reliability analysis and lifetime prediction of HfC-based ablation-resistant coatings.

To enhance ablation resistance in (Ta0.aNb0.aTi0.aHf0.aZr0.a)C-SiC (HEC-SiC) ceramics, the influence of SiC particle size on microstructure and ablation behavior was examined. With the addition of 20 wt% fine SiC particles, its relative density increases from 91.23 % to 97.79 %, and the grain size of the HEC phase decreased from 3.58 to 0.79 mu m. The fine SiC particles facilitated the formation of a continuous SiC network, thereby enhancing the thermal conductivity from 6.94 to 22.35 W/mK. This enhanced thermal conductivity contributed to reducing the ablation temperature from 2358 to 1721 degrees C during the ablation. The HEC-SiC sample with 0.5 mu m fine SiC particles added exhibits a mass and linear ablation rate of 0.05 mg/s and 0.67 mu m/s. The superior ablation resistance can be attributed to the reduced ablation temperature, altering the preferential oxidation sequence. This change in preferential oxidation led to the formation of a compact oxide scale with a multi-layer structure.

Carbon fiber-reinforced high-entropy carbide ceramics (Cf/HECs) are considered promising candidates for ultrahigh-temperature structural applications. The fiber-matrix interface plays a crucial role in determining the overall performance of these materials. This study proposes a novel interface design strategy inspired by the traditional Chinese mortise-tenon joint. In this design, microscale carbon spheres are deposited on the surface of carbon fibers to function as the "tenon", while the matrix serves as the corresponding "mortise". Furthermore, a TiC interfacial layer is introduced to improve the interfacial bonding through atomic diffusion. Owing to this distinctive interface structure, the resulting Cf/(TiZrHfNbTa)C-SiC composite exhibits excellent mechanical properties, with a flexural strength of 1053.33 MPa and a fracture toughness of 9.77 MPa & centerdot;m1/2. Additionally, the composite demonstrates remarkable thermal shock resistance, with a critical thermal shock temperature difference (Delta Tc) of 802 degrees C. It also displays superior ablation resistance, characterized by a linear ablation rate of 3.27 mu m & centerdot;s-1 and a mass ablation rate of 0.05 mg & centerdot;s-1.

Hafnium carbide (HfC) coatings are critical for protecting C/C composites in high-temperature and oxygen-rich environments. During service, ablation-induced chemical reactions and the associated volumetric expansion generate complex internal stress fields. Ultimately, these stresses drive the cracking and spallation of the coating. This work proposes a coupled chemo-mechanical ablation model that incorporates the feedback loop between stress-dependent reaction kinetics and chemical expansion strain. The model is implemented via a user-defined element (UEL) subroutine. It is employed to investigate the critical role of surface roughness in the coevolution of composition and internal stress within HfC coatings. Its predictive accuracy is validated against experimental post-ablation residual stresses and oxygen distribution profiles. The results identify the peak-to-valley transition regions as critical failure sites, where prolonged ablation (up to 40 s) elevates shear stress to 375 MPa. Furthermore, increasing surface roughness (Ra) from 4 to 12 mu m accelerates the degradation of oxygen barrier properties and amplifies the maximum tensile and shear stresses by over 48%. These findings provide fundamental insights into the failure mechanisms of HfC-based thermal protection systems.

High-entropy carbides are promising candidates for high-temperature structural applications owing to their exceptionally high melting points and outstanding thermal stability. However, their intrinsic brittleness severely restricts practical use. To address this limitation, carbon fiber reinforcement has emerged as a viable approach to enhance fracture toughness. In this study, pyrolytic carbon (PyC) was employed as a protective layer for the carbon fibers, while a TiC interface layer was incorporated to strengthen interfacial bonding. During high-temperature sintering, elemental diffusion at the interface promotes chemical interactions. The findings reveal that TiC diffusion catalyzes the graphitization of PyC, resulting in the in-situ formation of a multilayer graphene (MLG) bonding structure at the fiber-matrix interface. Molecular dynamics simulations elucidate that MLG formation proceeds via a generation-redecomposition mechanism involving TiC. This in-situ-formed MLG significantly enhances interfacial adhesion, enabling the Cf/(TiZrHfNbTa)C-SiC composite to achieve remarkable mechanical performance, with a flexural strength of 652.87 MPa and a fracture toughness of 7.64 MPa m1/2 . Furthermore, the MLG significantly improved thermal conductivity, endowing the composite with excellent thermal shock resistance (with a critical temperature difference, ATc, of 692 degrees C) and superior ablation resistance (with linear and mass ablation rates of 3.75 mu m s-1 and 0.16 mg s-1, respectively). (c) 2026 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

Hafnium carbide(HfC)serves as a critical ablation-resistant coating for C/C composites used on the wing leading edges of high-speed vehicles during atmospheric re-entry[1-3].Under the action of high-temperature,oxidizing gas flow,the HfC coating forms a high-melting-point heterogeneous oxide layer,significantly delaying oxidation of the underlying material and pre-serving the structural integrity of the C/C composites[4].

To address the extreme thermal challenges in ultra-high temperature scenarios, a synergistic strategy combining layered toughening and N-doped modification was adopted to enhance the ablation resistance of HfC-based coatings. This study systematically explored the relationship between phase composition, multi-layer structure and anti-ablation performance through a two-stage progressive approach. The results demonstrate that the moderate N-doping (HfN0.25C0.75) significantly improves ablation resistance of HfC coatings. Building upon this foundation, an innovative TaC/HfN0.25C0.75 multilayer coating was successfully constructed, exhibiting 18.2 % and 16.1 % reductions in mass/linear ablation rates respectively compared to monolithic coatings after 120 s ablation. Notably, it maintained low ablation rates of 0.66 mg/s and 0.84 mu m/s even under cyclic ablation environment (30 s x 4). The excellent performance originates from two synergistic mechanisms: 1) Multilayer interfaces effectively release thermal stress through crack deflection, inhibiting through-thickness cracking; 2) In-situ formed Hf-Ta-O self-healing glassy phases combined with stable Hf6Ta2O17 phases provide dual functionality of oxygen barrier and structural stabilization. This work provides new insights into designing advanced thermal protection systems through multi-scale structural engineering and composition optimization.

Ultrafine boride solid solutions offer immense potential for extreme environmental applications, yet their rapid synthesis with nanoscale compositional control remains a challenge. Herein, we exploit ultrafast high-temperature sintering to achieve the rapid synthesis of a (HfxZr1u2212x)B2 solid solution with exceptional nanoscale homogeneity. The phase composition and evolution during solid solution formation, as well as the formation tendency with varying Hf/Zr molar ratios, were systematically investigated. First-principles calculations reveal a progressively enhanced tendency to form a single-phase solid solution with increasing Hf content, which is attributed to the lower solution energy (Esol) for Zr atoms incorporating into the HfB2 lattice compared with the reverse process. This finding is consistent with the result of a lower synthesis temperature for (Hf0.8Zr0.2)B2 (1700 u00B0C). In addition, (Hf0.8Zr0.2)B2 also exhibits superior phase and thermodynamic stability, as demonstrated by its more negative u0394Gmix, lower DOS value at Ef, and reduced average bond length. This work not only establishes an efficient pathway for powder synthesis but also delivers foundational insights for the rational design of multidiboride ceramics.

SiC ceramic lattice structures (CLSs) have become increasingly popular in engineering applications due to their remarkable specific strength and thermal properties. To investigate their quasi-static compressive mechanical behavior, binder jetting additive manufacturing technology was used to produce various configurations of SiC CLSs, specifically Edge Center Cubic (ECC), Face Center Cubic (FCC) and Gyroid-type triply periodic minimal surfaces, namely the Gyroid-sheet (GSH) and Gyroid-skeletal (GSK). The findings reveal that the GSH configuration exhibits the highest quasi-static compressive strength at similar to 54 MPa. The failure mechanism is characterized by a sequential propagation of damage. Micro-cracking initiates at points of peak tensile stress-specifically, at the nodes or on the strut surfaces. These cracks then extend through the strut cross-section. The failure of a single critical strut redistributes the load to its neighbors, inducing sequential overloading and fracture. This chain reaction ultimately leads to the catastrophic crushing of the entire structure along an inclined shear zone. This research offers valuable insights for optimizing the design and assessing the mechanical performance of SiC CLSs.

To mitigate the degradation of mechanical properties caused by high-temperature melt erosion and reactions during the reactive melt infiltration process for fabricating carbon fiber reinforced ultra-high-temperature ceramic matrix composites, this work proposes an in-situ protection strategy that utilizes chemical vapor infiltration to uniformly fabricate a PyC/SiC/ZrC multi-layer interface layer on carbon fibers, thereby avoiding damage to carbon fibers. The results showed that the introduction of a PyC/SiC/ZrC interface layer significantly increased the flexural strength of the prepared composites by 133.3% in comparison to composites with a single PyC interface layer. Besides, after ablation under oxygen acetylene flame for 240 s, the mass and linear ablation rates show significant reductions of 69.6% and 90.1%, respectively. The tailored PyC/SiC/ZrC multi-layer interface delivered dual functionality: (i) synergistically introducing multiple pathways for energy dissipation while shielding fibers from Zr-Si melt erosion through the multi-layer interface, thus enhancing mechanical properties; (ii) in-situ generating a protective ZrO2/SiO2 oxide barrier layer on fibers during ablation to improve ablation resistance. This work provides new insights and valuable references for the efficient preparation of ceramic matrix composites with excellent ablation protection and mechanical properties. (c) 2026 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

Although high-temperature heat treatment improves the thermal stability and ablation resistance of carbon/ carbon (C/C) composites, the generation of microcracks and the weakening of interfacial bonding strength severely reduce their mechanical properties. Herein, this work proposes a novel approach involving additional Isothermal Chemical Vapor Infiltration (ICVI) for heat-treated C/C composites (HT-C/C) to form re-carburizing composites (rHT-C/C), repairing defects generated during the heat treatment process and enhancing interfacial bonding. After additional ICVI, the flexural strength and interlaminar shear strength of rHT-C/C reaches 223.7 MPa and 14.9 MPa, respectively, representing increases of 45.8 % and 106.9 % compared to HT-C/C. The superior mechanical properties of rHT-C/C can be attributed to enhanced interface bonding combined with stepped crack propagation and a complex multi-directional crack network. This work provides a theoretical foundation and process optimization strategy for enhancing the mechanical performance of C/C composites, facilitating their application as high-temperature structural components.

Multicomponent (Hf,Zr,Ta)C ceramics are promising candidates for ablation-resistant coating materials applied in ultrahigh-temperature environments. However, the influence of compositional variations on their ablation behavior remains insufficiently understood. In this study, the effect of Ta content on the ablation resistance of (Hf,Zr,Ta)C coatings was systematically investigated. Moderate Ta addition promotes the densification of oxide scales, whereas excessive Ta reduces the thermochemical stability of the oxide scale, leading to increased ablation damage. The optimized composition, the T15 coating, exhibits superior ablation resistance, maintaining structural integrity for 300 s under an ~2160 u00B0C oxyacetylene flame. This enhancement is attributed to the co-formation of the (Hf,Zr,Ta)O2 and (Hf,Zr)6Ta2O17 phases. Ta5+ partially dissolves into (Hf,Zr)O2 (~5 at%), reducing the oxygen vacancy concentration and improving the oxidation resistance. Additionally, the Ta-rich liquid phase generated from the decomposition of (Hf,Zr)6Ta2O17 enhances oxide scale densification and contributes to structural stability during cooling through peritectic transformation. These results demonstrate that non-equimolar multicomponent carbides offer a feasible strategy for improving the ablation resistance of ultrahigh-temperature coatings.

To withstand the thermal gradients experienced by ablation-resistant coatings in extreme environments, we integrate a functionally graded design with the compositional engineering of multicomponent borides to enhance the ablation resistance and cyclic stability of a (Hf,Zr,Ti)B2-SiC composite coating. The coating, with compositional gradients in Si and Ti across its thickness, was deposited onto carbon/carbon composites using atmospheric plasma spraying. After three 120-s oxyacetylene flame cyclic tests above 2200 degrees C, the coating exhibited remarkable ablation resistance, with a linear recession rate of-0.15 mu m s-1. The resulting oxide scale comprises an outer porous, fine-grained, and lattice-distorted (Hf,Zr,Ti)O2 layer and an inner (Hf,Zr)O2-SiO2 composite layer. This hierarchical architecture merges high-temperature stability, thermal insulation, and oxidation resistance. The coating remained effective even after prolonged exposure (6 x 120 s); however, extended cycles led to (Hf,Zr,Ti)O2 grain coarsening and SiO2 volatilization, resulting in performance degradation. This study proposes an effective strategy to enhance the long-term ablation resistance of coatings, contributing to the development of advanced thermal protection systems. (c) 2025 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.