With the increasing demands placed on materials in extreme environments—such as hypersonic flight, advanced propulsion systems, and next-generation nuclear energy—the need for ultra-high temperature ceramics (UHTCs) with balanced mechanical performance has become critical. Zirconium carbide (ZrC), a leading UHTC candidate, offers an exceptional melting point and solid-state stability, yet its practical application has been constrained by two long-standing challenges: poor sinterability requiring prohibitively high processing temperatures, and intrinsic brittleness that limits structural reliability. While various strategies—including solid solution formation, second-phase reinforcement, and composite design—have been explored to address these limitations, achieving simultaneous improvement in both strength and toughness has remained elusive. Most existing approaches enhance one property at the expense of the other, highlighting the need for innovative microstructural design strategies that can overcome this trade-off.
Recently, a team of material scientists led by Boxin Wei from Harbin University of Science and Technology and Yujin Wang from Harbin Institute of Technology, China developed a novel multi-scale microstructure design for ZrC-based ceramics through a two-step in-situ reactive spark plasma sintering (SPS) process using ZrC, TiSi 2 , and B₄C as raw materials.
The team published their work in Journal of Advanced Ceramics on February 12, 2026.
“The core challenge we aimed to address was how to simultaneously enhance both densification behavior and fracture resistance in ZrC ceramics,” explained Boxin Wei, associate professor at the School of Materials Science and Chemical Engineering, Harbin University of Science and Technology, whose research focuses on ultra-high temperature ceramics and their composites. “Our approach was to leverage a carefully designed sequence of in-situ reactions that would not only promote low-temperature densification but also create a hierarchical microstructure with reinforcing phases operating at different length scales.”
The team’s design strategy centered on the reaction between TiSi 2 and B 4 C, which proceeds in two stages. During the first SPS step at 1600 °C, TiSi 2 preferentially reacts with B 4 C to form TiB 2 and primary SiC, while the released silicon subsequently reacts with the ZrC matrix to produce ZrSi 2 and secondary SiC. The two-step sintering schedule—3 minutes at 1600 °C followed by 10 minutes at 1800 °C—was carefully designed to separate reaction-dominated and diffusion-dominated processes. This approach allowed complete in-situ reactions, liquid-phase sintering, and interdiffusion of Zr and Ti, leading to the formation of (Zr,Ti)C and (Ti,Zr)B 2 solid solutions.
“The two-step process is essential to our success,” noted Yujin Wang, professor at the Institute for Advanced Ceramics, Harbin Institute of Technology. “The lower-temperature hold prioritizes completion of the in-situ reactions, generating a high density of fine TiB 2 and SiC nuclei while intentionally limiting matrix grain growth. With these pinning phases already dispersed throughout the microstructure, the subsequent high-temperature sintering achieves full density while the nanoscale particles effectively suppress grain coarsening from the outset.”
With the addition of 30 mol% TiSi 2 and 15 mol% B 4 C, the resulting ZTS-30B ceramic exhibited a refined sub-microstructure with grain sizes below 500 nm, achieving a flexural strength of 824 ± 46 MPa and fracture toughness of 7.5 ± 0.5 MPa·m 1/2 —values that substantially exceed those of most previously reported ZrC-based materials.
“The performance enhancement arises from a true multi-scale synergistic mechanism,” explained Wei. “At the atomic scale, solid solution strengthening from (Zr,Ti)C and (Ti,Zr)B 2 introduces lattice strain fields that impede dislocation motion. At the nanoscale, both primary SiC—formed alongside TiB 2 —and secondary SiC—resulting from the reaction between silicon and ZrC—exert effective grain boundary pinning. At the microscale, plate-like TiB 2 grains promote toughening through crack deflection and bridging, while the higher-toughness ZrSi 2 phase provides additional energy dissipation during fracture.”
Detailed microstructural analysis revealed additional features contributing to mechanical performance. High-resolution transmission electron microscopy showed that secondary SiC particles maintain a specific crystallographic orientation relationship with the (Zr,Ti)C matrix, which reduces lattice mismatch and improves stress transfer. A high density of stacking faults was observed within β-SiC grains, further hindering dislocation motion and enhancing deformation resistance. At (Zr,Ti)C/(Ti,Zr)B 2 interfaces, an interdiffusion zone of approximately 9 nm was identified, indicating good chemical compatibility and interfacial bonding.
The team also compared the two-step sintering approach with conventional one-step processing. The one-step schedule showed a prominent densification rate peak at 1800 °C, indicating that intense in-situ reactions were still occurring at this stage—leading to accelerated Ostwald ripening and grain coarsening. In contrast, the two-step process exhibited a much lower rate peak at 1800 °C, confirming that major reactions were largely complete after the first step. Shrinkage analysis quantitatively confirmed that over 20% of total densification occurred during the 1600 °C hold for two-step samples, compared to significantly less for one-step processing.
“This work demonstrates that careful control of reaction sequence and thermal history can fundamentally alter the microstructure-property relationships in carbide ceramics,” commented Wei. “The in-situ formation of SiC-TiB 2 agglomerates is particularly noteworthy—these structures act as effective composite toughening units, with the interlocked SiC and TiB 2 phases deflecting propagating cracks and extending crack paths in ways that individual reinforcing phases cannot achieve alone.”
The researchers noted that the TiSi 2 addition serves multiple functions simultaneously: it provides a reactive sintering aid that promotes densification through transient liquid-phase formation, it supplies silicon for in-situ SiC formation, and it contributes titanium for subsequent solid solution formation with both carbide and boride phases. The resulting combination of solid solution strengthening, nano-scale pinning reinforcement, and micro-scale toughening represents a design strategy that could potentially be extended to other ultra-high temperature ceramic systems.
Other contributors include Zhichao Zhuang and Yang Yang from the School of Materials Science and Chemical Engineering at Harbin University of Science and Technology, China; Dong Wang from the School of Materials Science and Engineering at Anhui University of Technology, China; and Lei Chen from the Institute for Advanced Ceramics at Harbin Institute of Technology, China.
About Author
Boxin Wei is an associate professor and doctoral supervisor at the School of Materials Science and Chemical Engineering, Harbin University of Science and Technology, China. He serves as Deputy Director of the Heilongjiang Provincial Key Laboratory of Light Metal Material Modification and Green Forming Technology and has been recognized as a "High-Level Talent of Heilongjiang Province". He received his PhD from Harbin Institute of Technology in 2018. His research focuses on microstructure control of refractory metal carbide ceramics for nuclear applications.
Yujin Wang is a professor and doctoral supervisor at the School of Materials Science and Engineering, Harbin Institute of Technology, China. He serves as Deputy Director of the National Key Laboratory of Precision Welding and Joining of Materials Structures. He is a recipient of the National High-level Talent Program and the Program for New Century Excellent Talents of the Ministry of Education. His research focuses on tungsten-based composites, ultra-high temperature ceramics, high-entropy ceramics, and advanced nuclear materials. Prof. Wang has led more than 20 projects, including those funded by the National Natural Science Foundation of China. He has received four provincial and ministerial science and technology awards, two teaching achievement awards, and holds 22 authorized national invention patents. He has co-authored three books and published over 190 peer-reviewed papers with more than 3,600 SCI citations.
Funding
This work was financially supported by the National Natural Science Foundation of China (Nos. 52002098 and 52002003) and the Heilongjiang Provincial Natural Science Foundation of China (LH2023E080).
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 (1/34, 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
Journal of Advanced Ceramics
Achieving superior strength-toughness synergy in ZrC-based ceramics: an in-situ multiscale construction strategy via two-step reactive SPS process
12-Feb-2026