With the rapid development of modern industrial technology, the forming technology of ceramic matrix composites has become a key area of global research interest. Among numerous ceramic matrix composites, silicon carbide (SiC) has attracted sustained attention over recent decades due to its excellent mechanical properties, low density, corrosion resistance, strong oxidation resistance, good chemical and thermal stability, and outstanding friction and wear performance, making it a highly promising new material. Its application scenarios cover high-power microwave devices in commercial and military systems, electronic devices such as LEDs and MOSFETs, optical devices in automotive and aerospace fields, micro-electromechanical system (MEMS) sensors for harsh environments, gas and chemical sensors for internal combustion engines and furnaces, as well as photoelectric sensors in optoelectronics, demonstrating broad application prospects.
Si-SiC Composites
Si-SiC composites are mainly prepared by reaction sintering: SiC powder and graphite powder are mixed in a specific ratio and pressed into a green body, then infiltrated with molten or gaseous silicon at temperatures above 1410 °C under vacuum, allowing Si to react with graphite, ultimately forming a dense SiC-based ceramic composite. This material not only inherits the excellent characteristics of SiC itself, but also offers advantages such as low density, high mechanical strength, excellent thermal conductivity, and extremely low coefficient of thermal expansion, along with simple processing, low sintering temperature, controllable cost, and flexibility to combine with other forming processes. As a result, it plays a key role in many fields.
However, low fracture toughness is a critical weakness of reaction-bonded Si-SiC composites, severely limiting their application in more demanding scenarios. To address this drawback, current research mainly adopts two optimization approaches: one is to reduce the free Si content inside the material through process improvement, enhancing mechanical properties from the perspective of composition control; the other is to introduce a reinforcing phase into the material system, improving fracture toughness through structural optimization, thereby laying the foundation for further promotion of Si-SiC composites.
SiC-SiCf Composites
SiC-SiCf composites are the best among SiC-based ceramic composites, combining high-temperature resistance, high specific strength, and high specific modulus, while exhibiting pseudoplastic behavior similar to metals and low notch sensitivity. They have gradually become the preferred material for key hot-section components of aero-engines and thermal structural components of supersonic aircraft, holding an irreplaceable position in high-end equipment such as aerospace. These composites possess a complex multiscale hierarchical structure, which gives rise to different fracture mechanisms at various specific scales as well as cross-scale coupled failure characteristics, bringing both challenges and opportunities for precise performance control.
Through in-depth research, scientists have successfully established, from a macroscopic mechanical perspective, the relationship between internal constituent properties (such as fibers, matrix, and interface) and the mechanical behavior of SiC-SiCf composites, providing theoretical support for material performance optimization. In terms of preparation techniques, current mainstream methods include precursor infiltration and pyrolysis (PIP), chemical vapor infiltration (CVI)/chemical vapor deposition (CVD), reactive melt infiltration (RMI), hot pressing (HP), etc. Among these, CVI and PIP are traditional and most widely used techniques. CVI achieves densification through the decomposition, polycondensation, and deposition of precursor gaseous compounds at high temperature inside a porous medium, involving key steps such as gas diffusion, adsorption, surface reaction, and gas desorption; while PIP is more adept at filling large pores inside the material.
In actual production, considering the limitations of a single process, a combined CVI/PIP process is often employed. This combination integrates the advantages of continuous gas-phase deposition of CVI with the high efficiency of liquid-phase infiltration of PIP, enabling rapid densification of SiC-SiCf composites, effectively improving production efficiency and material performance, thus providing technical support for their large-scale application in high-end fields.
Summary
In summary, silicon carbide ceramics and their two core types of composites, each with unique performance advantages, demonstrate great application value in many key areas of modern industry. With continuous optimization of preparation processes and deepening performance research, these materials are bound to play an important role in more high-end scenarios, promoting technological upgrading and development in related industries.