Boron carbide (B4C) is a highly desirable material in the field of engineering ceramics due to its excellent properties, such as high hardness, chemical inertness, neutron absorption capability, and low specific weight. However, producing high-performance B4C ceramics has always been a challenge due to its covalent nature, which results in ultralow diffusivity and high melting points.
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Previous studies have shown that high-performance B4C ceramics can be achieved by pressure-assisted techniques at ultrahigh temperatures and pressures. In this article, we explore the use of dynamic sinter forging (DSF), a new sintering process that applies oscillatory pressure rather than static pressure to enhance the densification and mechanical properties of B4C ceramics.
The Challenge of Preparing B4C Ceramics
Boron carbide is a ceramic material that has many desirable properties, such as high hardness, low density, and good chemical resistance. However, the use of this material is limited by its poor sinterability and low fracture toughness.
Sintering is the process of compacting and forming a solid mass of material by heat or pressure without melting it to the point of liquefaction. The challenge in preparing B4C ceramics lies in achieving a high density and good mechanical properties while maintaining its desirable properties.
Due to the covalent nature of B4C, conventional sintering techniques have failed to produce high-performance B4C ceramics. To achieve the desired properties, pressure-assisted techniques at ultrahigh temperatures and pressures, such as spark plasma sintering (SPS) and high-pressure hot pressing (HP), have been used. These methods can achieve higher densities at lower temperatures compared to traditional sintering methods.
Although these techniques have been successful in producing high-performance B4C ceramics, they require expensive equipment and energy consumption, making them unsuitable for large-scale production.
What is Hot Oscillatory Pressing (HOP)?
Hot oscillatory pressing (HOP) is a new sintering process that applies oscillatory pressure rather than static pressure to enhance the densification and mechanical properties of various materials, including B4C.
The particle rearrangement, grain boundary sliding (GBS), and/or intragranular plastic deformation induced by oscillatory pressure enhance densification and mechanical properties. However, the densification mechanism of HOP is greatly reduced in the later stages of sintering when the relative density is high.
Forging, including hot forging (HF) and sinter forging (SF), are dieless techniques that subject materials to much greater shear strains than hot pressing, thus improving mechanical properties by increasing relative density, reducing process flaws, forming texture, and strengthening grain boundaries.
The effectiveness of hot forging and sinter forging has been proven in various ceramic systems, but static pressure was used in all previous works. Using oscillatory pressure in forging can further enhance the shear-related processes compared to static pressure.
Dynamic Sinter Forging (DSF) for B4C Ceramics
Dynamic hot forging (DHF), which applies oscillatory pressure to hot forging, has been proven to be much more efficient than conventional forging.
This technology was the focus of a study published in the Journal of the European Ceramic Society by a group of researchers from China's Dongguan University of Technology and Zhengzhou University of Aeronautics. They developed an innovative method of creating B4C ceramics that could revolutionize the way the material is made.
In their study, they tested four different methods of creating B4C ceramics: hot pressing, hot forging, dynamic hot forging, and dynamic sinter forging. Pre-sintered samples with a relative density of ~78% and a diameter of 20 mm were first prepared by hot pressing at 1700 o C and 20 MPa. The samples were then forged at 1900 o C and 70±10 MPa @ 5 Hz 2.
They found that the dynamic sinter forging method produced the strongest and hardest B4C ceramic samples, with a flexural strength of 935 MPa and a hardness of 39.2 GPa, which is significantly higher than any previously reported value for B4C.
To understand why this method produced such strong samples, the researchers analyzed the microstructure using advanced imaging techniques and found that the process created shear deformation in the samples, leading to their enhanced mechanical properties. This study suggests that dynamic sinter forging could be a promising new method for producing ultrahigh-performance B4C ceramics.
Such materials could have potential applications in industries where high strength and hardness are required, such as aerospace, defense, and automotive industries.
Conclusion
Dynamic sinter forging (DSF) is an innovative technique that shows great potential for manufacturing high-performance B4C ceramics. Unlike other pressure-assisted techniques that utilize static pressure, DSF employs oscillatory pressure, which improves densification and mechanical properties, making it more cost-effective and efficient.
The findings made by the research group have significant implications for the development of advanced engineering ceramics with exceptional mechanical properties.
The application of dynamic sinter forging can be extended to other ceramic systems, leading to the creation of cutting-edge materials for various industries. Moreover, the research provides new insights into the sinter forging mechanisms that could be leveraged to optimize processing parameters for other materials.
If optimized, DSF could become a mainstream method for producing B4C ceramics, which has a market worth about USD 215.1 million in 2021, and the market is expected to reach USD 260 million in 2028. This technology can be a game-changer in the market's growth.
However, further research is necessary to understand the underlying mechanisms fully. Also, researchers must optimize processing parameters to achieve even higher performance.
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References and Further Reading
Factors and Factors, (2021). Boron Carbide Market Size, Growth, Global Trends, Forecast to 2028 [Online]. Facts and Factors. URL https://www.fnfresearch.com/boron-carbide-market (accessed 3.9.23).
Fan, L., Song, X., Zhao, P., Yang, S., Zhang, M., An, L. (2023). Super strong B4C ceramics prepared by dynamic sinter forging. Journal of the European Ceramic Society S0955221923001772. https://doi.org/10.1016/j.jeurceramsoc.2023.02.069
He, Y.J., Winnubst, A.J.A., Verweij, H., Burggraaf, A.J. (2004). Improvement of mechanical properties of zirconia-toughened alumina by sinter forging. Journal Of Materials Science 29, 5868–5874. https://doi.org/10.1007/BF00366869
Liu, X., Pei, J., Liu, M., Wang, Z., Liu, L., Jing, L., Wu, Z. (2017). Microstructure and mechanical properties of textured TiB2 ceramic fabricated by combination of catalyst and hot–forging. Materials Chemistry and Physics 200, 217–222. https://doi.org/10.1016/j.matchemphys.2017.07.033
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