Thermal protection systems are essential for hypersonic vehicles operating under extreme conditions. Ultra-high temperature ceramics, particularly ZrB2- and HfB2-based diborides, are key materials for such applications due to their ultra-high melting points and excellent high-temperature performance. However, as hypersonic vehicles evolve toward multi-mission, reusable designs, the demand for oxidation resistance above 2000 ℃—especially under cyclic thermal conditions—has become increasingly critical.
Although multi-principal component (medium- and high-entropy) design has been shown to enhance the oxidation resistance of diboride ceramics, most previous studies have been limited to isothermal oxidation below 1500 ℃. The intrinsic oxidation behavior above 2000 ℃ remains largely unexplored, primarily due to the limitations of conventional testing methods. Traditional furnace heating suffers from slow ramp rates and limited maximum temperatures, while ablation techniques (oxyacetylene torch, plasma, wind tunnel) introduce aerodynamic erosion and non-uniform flow fields that physically remove or damage oxide scales, making it difficult to decouple intrinsic oxidation kinetics from thermomechanical effects. Laser heating, though capable of ultra-fast heating, produces large temperature gradients across the sample.
To address these challenges, a team of materials scientists led by Prof. Guo-Jun Zhang and Prof. Ji-Xuan Liu at Donghua University, China, utilized a rapid-heating furnace (UHS-3000, Tianjin Zhonghuan Electric Furnace Co., Ltd., China) equipped with a graphite heating element to establish an ultra-fast oxidation testing method capable of elevating specimens to 2300 ℃ in just 23 seconds (100 ℃/s heating rate) under flowing air. This ultra-fast heating profile effectively minimizes pre-oxidation during the transient stage, enabling more accurate evaluation of the intrinsic oxidation resistance of MEB ceramics under ultra-high-temperature conditions.
The team published their work in Journal of Advanced Ceramics on August 25, 2026.
The team systematically investigated the cyclic oxidation behavior of three representative compositions—(Zr1/4Hf1/4Ta1/4Ti1/4)B2, (Zr1/4Hf1/4Ta1/4Nb1/4)B2, and (Zr1/3Hf1/3Ta1/3)B2—along with monolithic ZrB2 as a reference. The samples underwent five 1-minute cyclic exposures at 2300 ℃, for a total of 5 minutes of cumulative holding time.
"We found that MEB ceramics form multi-layered oxide scales with substantially reduced thicknesses (99-125 μm), while monolithic ZrB₂ develops only a porous and cracked single-layer scale of 230 μm that offers negligible protection," said Prof. Liu. "Among the MEB compositions, the Ti-containing (Zr1/4Hf1/4Ta1/4Ti1/4)B2 exhibits the best overall oxidation resistance, with the thinnest oxide scale, the densest outer layer, the least mass loss, and intact scale integrity with no interfacial separation after five thermal cycles."
The superior performance of the Ti-containing composition arises from the bifunctional role of the element Ti. At high temperatures, Ti forms a liquid oxide phase (enriched in Ti and Ta) that wets and densifies the outer (Zr, Hf)O2-based layer—derived from the structural elements Zr and Hf—creating an effective oxygen diffusion barrier. Simultaneously, during cooling, Ti modifies the crystallization environment of Ta2O5, promoting the precipitation of a porous needle-like Ta2O5 network in the inner layer. This porous skeleton provides local strain-accommodation space, effectively relaxing thermal stress accumulation and preventing crack propagation and interfacial delamination during subsequent thermal cycles.
"This work demonstrates that the oxidation resistance of multi-principal component non-oxide ceramics is governed by elemental functionality rather than by configurational entropy alone," emphasized Prof. Zhang. "Our findings provide a design principle that can be extended from equimolar to non-equimolar systems for reusable thermal protection applications."
The team's findings not only establish a rapid-heating method for conveniently and efficiently evaluating ultra-high-temperature oxidation of materials but also reveal a fundamental mechanistic insight: the synergy between structural elements and the functional elements is the key to designing oxidation-resistant multi-principal component ceramics: structural elements provide the high-melting-point oxide skeleton, while functional elements densify the outer layer and induces a porous network in the inner layer upon cooling that buffers thermal stress accumulation during subsequent cycles.
About Author
Yizhou Cao (First Author) received his master's degree from the College of Materials Science and Engineering at Donghua University, China, in 2026. His research focuses on the preparation and oxidation resistance of high-entropy boride ceramics.
Ji-Xuan Liu (Corresponding Author) is a professor at the College of Materials Science and Engineering, Donghua University.
Guo-Jun Zhang (Corresponding Author) is a professor at the College of Materials Science and Engineering, Donghua University. He is an Academician of the World Academy of Ceramics and a council member of the Advanced Ceramics Branch of The Chinese Ceramic Society.
Funding
The present work was financially supported by the National Natural Science Foundation of China (No.52332003, 52371023, 52032001).
DOI LINK: 10.26599/JAC.2026.9221361
About Journal of Advanced Ceramics
Journal of Advanced Ceramics (JAC) is an international academic journal that presents the state-of-the-art results of theoretical and experimental studies on the processing, structure, and properties of advanced ceramics and ceramic-based composites. JAC is Fully Open Access, monthly published by Tsinghua University Press, and exclusively available via SciOpen . JAC's 2025 IF is 14, ranking in Top 1 (1/34, Q1) among all journals in "Materials Science, Ceramics" category, and its 2025 CiteScore is 24.6 (6/133) in Scopus database. ResearchGate homepage: https://www.researchgate.net/journal/Journal-of-Advanced-Ceramics-2227-8508
