HUANG Xinhua ¹, YI Chenhao ², QIU Riliang ¹, XIAO Qiankun ¹, YU Huan ¹, XIAO Zhuohao ¹

(1. Jingdezhen Ceramic University, Jingdezhen 333403, Jiangxi, China; 2. Jiangxi Guanyi Grinding Co., Ltd.,

Yichun 330700, Jiangxi, China)

Extended abstract:

[Significance] Microcrystalline ceramics based composite materials can not only achieve effective densification through their crystal phase composition and viscous flow ability of residual glass phase, but also flexibly control their thermal properties, providing a unique process window and interface control space for fiber or whisker reinforcement that is different from traditional crystalline ceramics. By introducing continuous or short fibers, whiskers or carbon nanotubes as nano reinforcements, fiber/whisker reinforced microcrystalline ceramic composites are expected to have synergistic improvement in strength, stiffness and fracture toughness, while maintaining low density. Combined with thermal expansion matching design, this type of material can exhibit excellent thermal dimensional stability, which meets the requirements of high-performance, high thermal stability and strong environmental tolerance in aerospace thermal structures, precision thermal stability components and electronic packaging. Therefore, systematically sorting out the composition, preparation path interface and thermal mismatch of these materials is of great significance for promoting engineering application.

[Progress] (1) Reinforcement system and multi-scale synergy. Carbon based reinforcement systems (such as continuous or short cut carbon fibers, carbon nanotubes) have shown outstanding performance in improving toughness and achieving electrical functionalization, but their high-temperature antioxidation stability is still the main limiting factor. Silicon carbide fiber or whisker reinforced systems have more advantages in high-temperature load-bearing and antioxidant potential. New reinforcement materials, such as mullite whiskers and lithium silicate whiskers, provide new avenues for the functionalization and environmental adaptability of materials, due to their excellent thermal matching and chemical stability. At present, the multi-scale collaborative reinforcement strategy, with integration of fibers, whiskers and nanoparticles, has become an effective method for achieving synchronous improvement of strength and toughness. (2) The precursor preparation and molding process are diversified. Sol-gel penetration method is conducive to reducing the densification temperature of materials and improving the designability of matrix components. Melt crystallization method is suitable for the preparation of high-efficiency and bulk materials. The casting method facilitates the regulation of reinforcement orientation and the construction of layered structures. In addition, processes, such as electrophoretic deposition, wire drawing and extrusion, provide alternative solutions for the forming and process consistency of specific shaped components. Although there are various process routes, their core lies in achieving precise control of liquid phase viscosity, reinforcement penetration coating effect and densification process window. (3) Interface engineering and thermal mismatch control. The interface bonding strength directly determines the load transfer efficiency and crack propagation path. Combining too strong interfaces can easily lead to cracks directly penetrating the fibers, suppressing fiber pull-out energy dissipation and causing brittle fracture. However, a weak interface makes it difficult to achieve effective load transfer. By designing in-situ generated carbon rich layers or introducing structures, such as coatings and intermediate layers, the aim is to achieve “controllable debonding” and frictional energy dissipation at the interface. Meanwhile, residual stresses caused by differences in thermal expansion coefficients may induce microcracks or interface debonding. Moderate thermal mismatch can sometimes introduce beneficial compressive stress in the matrix, but excessive mismatch would lead to interface cracking and damage to the reinforcement. Therefore, it is necessary to regulate the thermal expansion coefficients of the matrix and reinforcement and design a buffer interface layer to manage it.

[Conclusions and prospects] Overall, the performance of fiber/whisker reinforced microcrystalline ceramic composites is determined by the characteristics of the matrix crystal phase and residual glass phase, the geometric shape and distribution orientation of the reinforcement, as well as the interface bonding state and residual stress. For practical applications, future research needs to follow the integrated approach of “material design, molding manufacturing and application verification”. Firstly, a multi-scale collaborative design method should be established for composition, crystal phase and interface to obtain stable and reproducible toughening equilibrium ranges. The second issue is to break through the low-cost near net forming and defect control technology of complex components, while improving the consistency of the manufacturing process. The third one is to systematically evaluate the evolution law and performance retention rate of the interface structure of materials under high-temperature oxidation, hot corrosion and thermal cycling conditions, thus developing highly reliable coating or gradient layer protection systems. Lastly, it is important to promote the integrated design and standardized verification of structural and functional aspects in cutting-edge directions, such as electronic packaging and biomedicine, thereby driving these materials from excellent laboratory performance to practical component level applications.

Key words: fiber/whisker; microcrystalline ceramics; high intensity; fracture toughness; dimensional stability