Novel precipitation–densification strategy enables hardness–toughness synergy in in-situ composite ceramics of triphase silicon nitride ceramics

Achieving a balance between high hardness and high toughness is a critical challenge in advanced structural ceramics. Silicon nitride (Si₃N₄) ceramics have attracted considerable attention for demanding engineering applications because of their excellent mechanical properties and diverse polymorphs with distinct structural and mechanical characteristics. Among these polymorphs, γ-Si₃N₄ exhibits high hardness, while β-Si₃N₄ commonly develops elongated grains that can contribute to crack deflection and crack bridging. These complementary characteristics make multiphase Si₃N₄ an attractive candidate for achieving synergistic mechanical properties.

Generally, multiphase silicon nitride ceramics are developed by combining different phases through conventional processing or by controlling phase transformations during sintering. However, the different transformation kinetics of Si₃N₄ polymorphs, together with rapid volume shrinkage during phase transitions, make it difficult to simultaneously regulate phase composition, microstructure, densification, and interfacial bonding. In particular, rapid γ-phase formation and growth are accompanied by defect formation, while the substantial volume shrinkage during phase transition adversely affects interfacial bonding. Therefore, an effective strategy is needed to exploit the intrinsic phase-transition behavior of Si₃N₄ for coordinated microstructural and interfacial engineering.

Recently, a team of material scientists led by Professors Bingbing Liu and Hu Tang from Jilin University, China, reported the construction of triphase silicon nitride through a novel phase-transition-regulated precipitation–densification strategy.

This work not only demonstrates a route to construct a uniformly distributed triphase silicon nitride microstructure with strong interfacial bonding, but also provides a new strategy for exploiting phase-transition kinetics to achieve a synergistic combination of hardness and fracture toughness in structural ceramics.

The team published their work in Journal of Advanced Ceramics on August 28, 2026.

“In this work, we developed a phase-transition-regulated precipitation–densification strategy based on the distinct transformation kinetics of α-, β-, and γ-Si₃N₄. γ-Si₃N₄ was first rapidly precipitated at elevated temperature to introduce the hard phase. The temperature was subsequently lowered to regulate γ-phase growth and mitigate defects associated with rapid phase transformation and volume shrinkage. Meanwhile, the residual α-Si₃N₄ was promoted to transform into β-Si₃N₄, while progressive densification of the ceramic was achieved,” said Hu Tang, professor at the State Key Laboratory of High Pressure and Superhard Materials, Synergetic Extreme Condition High-Pressure Science Center, College of Physics, Jilin University, Changchun, China, and an expert whose research interests focus on the synthesis and applications of high-performance structural materials under high-temperature and high-pressure conditions.

“The resulting ceramic consists of three uniformly distributed Si₃N₄ polymorphs, with α-, β-, and γ-Si₃N₄ serving complementary roles in mechanical performance. The γ phase provides hardness enhancement, while elongated β-Si₃N₄ grains contribute to crack deflection, crack arrest, crack branching, repeated crack initiation, and crack bridging. The in-situ composite interfaces between different polymorphs further facilitate cooperative load transfer and regulate crack propagation,” said Tang.

“Through this phase-transition-regulated strategy, the triphase silicon nitride ceramic achieved a Vickers hardness of 26.34 ± 0.61 GPa and a fracture toughness of 6.02 ± 0.48 MPa·m^1/2. These results demonstrate that phase transformation can be actively harnessed to coordinate phase composition, microstructure, and interfacial structure, rather than being regarded simply as a phase evolution process,” said Tang.

However, further research is still needed to investigate the broader applicability of phase-transition-regulated microstructural engineering to other multiphase ceramic systems and to further optimize the balance between hardness, toughness, and structural reliability. In this regard, the phase-transition engineering concept may provide new opportunities for the development of high-performance structural ceramics for demanding engineering applications.

Other contributors include Shucheng Liu, Bingtao Feng, Zhaodong Liu and Bingbing Liu from Jilin University, China.

About Author

Hu Tang is a professor at the State Key Laboratory of High Pressure and Superhard Materials, Synergetic Extreme Condition High-Pressure Science Center, College of Physics, Jilin University, China. He received his PhD degree in Materials Science from Yanshan University in 2018 and subsequently conducted postdoctoral research at the Beijing High Pressure Science Research Center, Southern University of Science and Technology, and the University of Bayreuth. His current research focuses on the high-temperature and high-pressure synthesis and development of high-performance novel structural materials. He has published more than 30 SCI papers in journals including Nature, Nature Materials, Advanced Materials, and Journal of Materials Science & Technology.

Funding

This work was supported by the National Natural Science Foundation of China (Nos. 12374201, U25A20192, and U2032215), the National Key R&D Program of China (No. 2023YFA1406200), Fundamental and Interdisciplinary Disciplines Breakthrough Plan of the Ministry of Education of China (JYB2025XDXM311), the Jilin Province Major Science and Technology Program, China (No. 20240211002GX), the Science and Technology Development Project of Jilin Province (No. SKL202402004), the Science and Technology Development Plan Project of Changchun, China (No. 23GZZ18), the Xiaomi Young Talents Program.

DOI LINK: 10.26599/JAC.2026.9221366

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