Silicon nitride (Si3N4), a widely adopted engineering ceramic, demonstrates significant potential in emerging applications such as Insulated Gate Bipolar Transistor (IGBT) packaging, semiconductor substrates, and bioceramics due to its high theoretical thermal conductivity and excellent biocompatibility. However, liquid-phase sintering, the dominant densification mechanism for Si3N4, restricts further performance enhancements. The inherent phase transformation of this high-temperature process typically yields a β-phase-dominated microstructure. The precipitated β-phase grains exhibit anisotropic growth with high growth rates along certain crystallographic directions, leading to the formation of an interlocking microstructure that enhances strength and toughness. Nevertheless, this high growth rate also tends to cause grain coarsening, making it difficult to precisely control microstructure evolution and thus limiting further improvements in properties.
High-pressure lowers the required densification temperature below phase transition point, thereby enabling the fabrication of dense, equiaxed α-phase Si3N4 ceramics characterized by high hardness but intrinsically low toughness. Due to their distinct lattice stacking sequences, the α and β phases essentially represent a high-hardness phase and a high-toughness phase, respectively. The adjustments of processing parameters and powder composition to content allow the tuning of toughness and hardness by manipulating phase content, but they cannot overcome the performance bottleneck caused by the phase composition and grain morphology inherent to conventional sintering. Although novel silicon nitride architectures with a certain degree of compromise between toughness and hardness can be synthesized through complex processing or extreme high-pressure techniques, these high-cost approaches have yet to achieve a definitive breakthrough in the synergistic optimization of both properties。
Notably, the previous study on high-pressure-assisted liquid-phase sintering revealed that high pressure promoted phase transformation through a mechanism involving stress-induced interfacial migration. This mechanism altering the microstructure by transcending the thermodynamic constraints of phase transformation avoided the performance limitations caused by microstructural and phase composition in conventional sintering.
Recently, a team of materials scientists led by Zhengyi Fu from Wuhan University of Technology conducted a deeper investigation into the microstructural evolution and grain growth kinetics during metastable phase transitions under high-pressure stress. This work can provide insights that break the limitations of traditional liquid-phase sintering, offering a theoretical basis and guidance for the development of a new generation of high-performance Si₃N₄ ceramics.
The team published their work in Journal of Advanced Ceramics on April 21, 2026.
In this study, samples were prepared using 2%, 4%, and 6% sintering aids and sintered at 1550 °C and 1600 °C. which depends on previous experience with additive content and sintering temperature, and to prevent grain coarsening and performance degradation induced by excessive liquid phase formation.
The effects of high pressure applied above the phase transformation temperature on phase transformation and grain growth during the final stage of densification are shown to define the microstructure evolution through interfacial stress, which varies with the liquid phase content. A low additive content (2 wt%) yielded high-hardness α-Si₃N₄, while increasing the liquid phase to 4–6 wt% facilitated complete phase transformation, thus resulting in high strength and toughness. Notably, the sample with 6 wt% additive sintered at 1600 °C achieved a simultaneous enhancement of strength (982 ± 63 MPa), toughness (10.2 ± 0.3 MPa·m¹/²), and hardness (20.1 ± 0.3 GPa). This improvement in performance is attributed to a unique twisted intergrowth mechanism, which involves stress-induced compression and shear during the ordered coalescence of precipitated particles during phase transformation.
About author:
Xiao-Wei Qin is a Ph.D. candidate at Wuhan University of Technology, affiliated with the State Key Laboratory of Advanced Technology for Materials Synthesis and Processing. Under the supervision of Research Professor Wei Ji, his academic specialization focuses on high-performance structural ceramic materials. His current research primarily investigates the fundamental principles of novel sintering technologies for advanced ceramics, particularly nitrides and oxides.
Funding:
This work was financially supported by the National Natural Science Foundation of China (52322207, 92163208, and 52494933), Fundamental and Interdisciplinary Disciplines Breakthrough Plan of the Ministry of Education of China (JYB2025XDXM408), the Natural Science Foundation of Hubei Province (2025AFA043, 2025CSA004), and the Independent Innovation Projects of the Hubei Longzhong Laboratory (2022ZZ-11).
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
