For decades, materials scientists have faced a persistent challenge with advanced ceramics: increasing hardness often comes at the cost of fracture resistance. This hardness-toughness trade-off is particularly severe in transition metal carbides, which are widely considered for high-temperature equipment, cutting tools, protective coatings, and other extreme-service components. While spinodal decomposition can separate a solid solution into nanoscale compositionally distinct phases and create dense interfaces that strengthen ceramics and deflect cracks, the intrinsic brittleness of carbides still limits the toughening achievable through this single mechanism.
Now, a team of researchers at Shandong University has introduced a different solution. Using (Ti, Zr, V, Nb, Mo)C high-entropy carbide as a model system, they demonstrated that spinodal decomposition and precipitation can be activated simultaneously through controlled aging. The coexistence of these two phase-transformation pathways creates a hierarchical microstructure that combines different interfaces and defects, enabling a synergistic improvement in both hardness and toughness.
The team published their work in Journal of Advanced Ceramics on August 10, 2026.
“For a long time, spinodal decomposition has been viewed as an effective way to strengthen carbide ceramics, but relying on one phase-transformation mechanism still places a limit on toughness,” says Weibin Zhang, the corresponding author of the study and a professor at Shandong University. “Our idea was to make two different transformations work together in the same ceramic, so that each could contribute a distinct strengthening and toughening effect.”
The study revealed a complex microstructural evolution. After aging, the initially single-phase solid solution developed coexisting (Ti, V, Mo)C-rich and (Zr, Nb)C-rich spinodal domains together with ZrC-rich precipitates. The spinodal phases formed semi-coherent interfaces associated with lattice strain and dense dislocation structures, while the precipitates formed incoherent interfaces and contained abundant nanotwins and stacking faults.
“The key is that these two phase transformations do not simply coexist; they generate different interfaces and defect structures that complement one another,” Zhang explains. “The semi-coherent spinodal interfaces provide extended strain fields and promote dislocation formation, while the incoherent precipitate interfaces act as strong local pinning sites. Nanotwins and stacking faults inside the precipitates provide additional barriers and energy-dissipation pathways, creating a multi-scale network that resists both deformation and crack propagation.”
The results were striking. The team identified aging at 1300 °C for 20 h as the optimal processing condition. Under this condition, hardness increased by about 36% and fracture toughness by about 45% compared with the as-sintered state. However, the researchers also found that excessive aging or higher temperatures caused coarsening of the phase-separated structure and precipitates, together with recovery and annihilation of dislocations, reducing the mechanical benefits. This highlights the importance of precisely regulating phase-transformation kinetics.
Looking ahead, the team plans to explore whether this dual-transformation design principle can be extended to other advanced ceramic systems. “Our ultimate goal is to develop a more general strategy for overcoming the hardness-toughness trade-off in refractory ceramics,” adds Zhang. “High-entropy compositions provide a broad thermodynamic design space, and we believe that deliberately coupling multiple metastable phase transformations could open new opportunities for creating ceramics that combine extreme hardness with improved damage tolerance for demanding aerospace, machining, nuclear, and other structural applications under extreme conditions, without introducing softer external phases.”
Other contributors include Zhixuan Zhang, Na Li, Zongyao Zhang, Jiatai Zhang, Qiang Zhang, Guorui Chang, and Weili Wang from Shandong University.
About Author
Weibin Zhang is a professor and doctoral supervisor at the School of Materials Science and Engineering, Shandong University. He is the Chief Scientist of a Young Scientist Project under the National Key Research and Development Program of China and a Qilu Young Scholar at Shandong University. His research has long focused on high-performance hard and wear-resistant ceramics and materials genome engineering. He has led more than 10 national and provincial-level research projects, including the National Key Research and Development Program of China, the National Natural Science Foundation of China, the Key Research and Development Program of Shandong Province, and the Key Research and Development Program of Henan Province. He has published more than 100 SCI-indexed papers in journals including J. Adv. Ceram. , Adv. Funct. Mater. , Adv. Energy Mater. , Acta Mater. , J. Mater. Sci. Technol. , and Rare Met. , and has been granted more than 10 national invention patents. He also serves as an expert on the General Expert Panel of the National Key Research and Development Program on “High-end Functional and Intelligent Materials” and as a Young Editorial Board member of several journals, including Materials Genome Engineering Advances , Journal of Materials Engineering , and Journal of Aeronautical Materials .
Funding
This work was supported by the National Key Research and Development Program of China (No. 2023YFB3712600).
DOI LINK : 10.26599/JAC.2026.9221357
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
Journal of Advanced Ceramics
Multi-scale hardening and toughening of (Ti,Zr,V,Nb,Mo)C high-entropy carbides through coexisting phase separation and precipitation mechanisms
10-Aug-2026