High-pressure synthesis, mechanical properties and oxidation behavior of advanced boron-containing α/β-Si3N4/Si ceramics using polymer-derived amorphous SiBN ceramics

The preparation of dense Si₃N₄-based ceramics has attracted great attention due to the achievable improvements in mechanical properties and high-temperature oxidation resistance. In general, the densification of nitride ceramic materials is achieved by liquid-phase sintering using oxidic-based sintering additives such as Al₂O₃ and Y₂O₃ due to their high covalent bond. However, the sintering additives usually remain as crystalline or amorphous phases at grain boundaries and/or at grain junctions. These intergranular phases soften at high temperatures, causing creep and reducing the high temperature behavior. These features limit the application of nitride ceramics at high temperatures under harsh conditions.

Within recent years, considerable interest has been developed in the preparation of additive-free Si₃N₄-based ceramics. Therefore, it is still a challenge to synthesize fine-grained α-Si₃N₄ or α/β-Si₃N₄ bodies with high hardness by conventional pressure sintering methods. In addition, amorphous materials possess much more disordered structure, highly homogeneous sites down to the atomic scale, composition flexibility, isotropic molecular diffusion and more percolation pathways in solid mixtures compared to crystalline materials, providing them with more densification possibilities. The polymer derived ceramic (PDC) route is an attractive method for the fabrication of amorphous ceramics due to the facile tailoring of element content at molecular level, exhibiting significant advantages compared to the traditional ceramic processing techniques.

Recently, two teams of material scientists led by Prof. Ralf Riedel from Technical University of Darmstadt, Germany and Prof. Tian Cui from Ningbo University, China, first reported microstructural evolution, mechanical properties (hardness and fracture toughness) and oxidation behavior (1400 ^oC, 50 h) of advanced boron-containing α/β-Si₃N₄/Si ceramics prepared by high pressure technique combining the PDC route. This work not only explains the effect of boron on suppressing phase transformation from α-Si₃N₄ to β-Si₃N₄, but also clarifies that the incorporation of boron in Si-N network is beneficial for the improvement of mechanical properties and oxidation resistance of the obtained Si₃N₄-based ceramics.

The team published their work in Journal of Advanced Ceramics on August 22, 2024.

In this report, the authors synthesized dense additive-free boron-containing α/β-Si₃N₄/Si ceramics using high pressure technique combined with polymer-derived ceramic route. The phase evolution of the obtained samples at different temperatures was investigated using XRD Rietveld Refinement and STEM techniques. The results show that phase transformation from α→β-Si₃N₄ is strongly suppressed due to the presence of boron in the Si₃N₄ matrix.

Furthermore, the authors found that the presence of boron has a significant influence on their mechanical properties and oxidation behavior. The mechanical properties of the as-prepared samples were measured and the maximum hardness and fracture toughness of boron-rich SiBN samples reaches up to 14.8 GPa and 7.96 MPa·m^1/2, respectively. The hardness of the obtained boron-rich SiBN samples is stable at 300 ^oC. The authors also pointed out that SiBN1-derived Si₃N₄ samples show higher fracture toughness than most of the reported Si₃N₄-based materials but without sacrificing hardness, even including 30 wt% of low hardness Si (~ 11 GPa). Accordingly, the resultant boron-containing Si₃N₄ ceramics possess both high hardness and fracture toughness simultaneously. Therefore, the boron-containing Si₃N₄ ceramics prepared by high-pressure technique is considered to be a potential candidate material for structural applications.

Besides, the Si₃N₄ ceramics containing moderate amounts of boron (Si:B=5:1) exhibit remarkable oxidation resistance in comparison to the boron-free Si₃N₄ ceramics owing to the formation of a borosilicate glass as a protective layer, suggesting potential structural applications of boron-containing Si₃N₄ products in high-temperature oxidation and corrosion environments. Therefore, this work provides a guidance for the synthesis of boron-containing α/β-Si₃N₄-based ceramics with excellent mechanical properties and oxidation resistance.

Other contributors include Wei Li, Jingxue Ding, Marc Widenmeyer, Ying Zhan, Anke Weidenkaff and Ralf Riedel from the Department of Materials and Earth Sciences at Technical University of Darmstadt in Germany; Siwen Cui, Xiaoqi Zhang and Pinwen Zhu from the College of Physics at Jilin University in Changchun, China; Zhaoju Yu from the Key Laboratory of High Performance Ceramic Fibers at Xiamen University in Xiamen, China.

This work was supported by the National Natural Science Foundation of China (No.12204254), the Natural Science Foundation of Zhejiang province (No. LQ23A040005), Program for Science and Technology Innovation Team in Zhejiang (2021R01004) and the German Ministry of Education and Research (project number: 03SF0618B).

About Author

Shuailing Ma is an associate research fellow at Institute of high-pressure physics (IHPP), Ningbo University. He received PhD at Jilin university at 2017. He worked at HPSTAR, DESY from 2019 to 2022. He then joined the IHPP at Ningbo. His current research focuses on the design and synthesis of hard materials under high pressure and high temperature.

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 2023 IF is 18.6, ranking in Top 1 (1/31, Q1) among all journals in “Materials Science, Ceramics” category, and its 2023 CiteScore is 21.0 (top 5%) in Scopus database. ResearchGate homepage: https://www.researchgate.net/journal/Journal-of-Advanced-Ceramics-2227-8508

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