Due to rapid advancement of aerospace industry, severe aerodynamic heating phenomenon results in the service temperature of thermal insulation component above 2000°C. However, common oxide thermal insulation materials cannot survive in elevated ultrahigh temperature due to their relatively low melting points. Hence, it is urgent and necessary to develop new ultrahigh-temperature insulation materials with low density, high strength, extremely low thermal conductivity, and outstanding thermal stability. As is well known, ultrahigh-temperature ceramic (UHTC) is a series of promising ultrahigh-temperature thermal insulation material, especially for carbide, which stems from their high melting temperature (>3000°C), excellent thermochemical stability, high strength and ablation resistance. Nevertheless, high density and high intrinsic thermal conductivity hinder their further application in lightweight ultrahigh-temperature thermal insulation field.
Recently, a team of material scientists led by Jingyang Wang from Institute of Metal Research, Chinese Academy of Science, propose a strategy of multiscale collaborative design which combines high-entropy effect and porous structure to solve the above drawbacks and develop a novel porous dual-phase high-entropy ultrahigh-temperature ceramic (TiZrHfNbTa)C-(TiZrHfNbTa)B2. The as-prepared porous ceramic possesses fascinating properties, including ultrahigh porosity, low density, high strength, low thermal conductivity, and excellent oxidation resistance. The research provides a potential alternative for critical materials in ultrahigh-temperature thermal insulation.
The team published their work in Journal of Advanced Ceramics on July 30, 2025.
"High-entropy effect in multi-element composition can obviously increase lattice distortion resulting in lower thermal conductivity, while the introduction of porous structure with ultrahigh porosity can effectively decrease density and thermal conductivity of UHTC at the same time." said Jingyang Wang, the professor at Institute of Metal Research, Chinese Academy of Sciences (CAS), "Significantly, an extra dual-phase composition design can compensate for each other's drawbacks: borides phase in the matrix can make up for the deficiency of oxidation resistance for carbides; conversely, high thermal conductivity of borides can be restrained by the existence of carbides.''
The researchers utilize foam-gelcasting-freeze drying and in-situ pressureless reaction sintering techniques to prepare porous dual-phase high-entropy UHTC. According to SEM and TEM results, the porous samples have uniform pore size and random alternating distributions of HEB particles and HEC particles. Two-phase components help to form tremendous number of grain boundaries to inhibit the grain growth of each other. And then the generated small grains are beneficial to obtain high strength and low thermal conductivity. By using EDS technique, it is worth noting that the distribution of elements is homogeneous at micro and nano levels. Moreover, the dual phases could also result in abundant interface thermal resistance and further decrease the thermal conductivity of UHTC. The prepared porous ceramics possess excellent overall properties, such as ultrahigh porosity of 96.4%–90.1%, low density of 0.31–0.87 g/cm3, high strength of 0.45–4.17 MPa, and low thermal conductivity of 0.202–0.281 W/(m·K), as well as good oxidation resistance. The research results indicate that the highly porous dual-phase high-entropy UHTC has broad application prospect in ultrahigh-temperature thermal insulation field.
However, more delicate research works are still needed to explore the oxidation behaviors of porous dual-phase high-entropy UHTC. In this regard, the analysis of oxidation kinetics under isothermal oxidation would be pursued in future work.
This work was supported by the National Natural Science Foundation of China under Grant Nos. U21A2063, U2441266, 52372071, 52302076, International Partnership Program of the Chinese Academy of Sciences under Grant No.172GJHZ2022094FN and LiaoNing Revitalization Talents Program under Grant Nos. XLYC2203090.
About Author
Jingyang Wang is the Vice President of Liaoning Academy of Materials (LAM) and the director of Institute of Coating Technology for Hydrogen Gas Turbines in LAM. He is also a professor of Advanced Ceramics and Composites Division, Institute of Metal Research, Chinese Academy of Sciences (CAS). His research interests are focused on fundamental exploration and technological developments of structure ceramics, ceramic-matrix-composites, and high temperature thermal barrier coating and environmental barrier coating for extreme environmental applications.
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 2024 IF is 16.6, ranking in Top 1 (1/33, Q1) among all journals in "Materials Science, Ceramics" category, and its 2024 CiteScore is 25.9 (5/130) in Scopus database. ResearchGate homepage: https://www.researchgate.net/journal/Journal-of-Advanced-Ceramics-2227-8508
