Fabrication of High Performance 2.5D SiO_2f/Si₃N₄‐BN Composites for High‐temperature Application

Abstract

A radar window for a reentry vehicle should process critical properties, such as high mechanical properties which are resistant to stress failure induced by large thermal impact, high microwave transmission efficiency at room and high temperature, and very high ablation resistance. Fused silica, BN and Si 3 N 4 ceramics are the three popular materials for such applications, but they are limited in some fields for their intrinsic disadvantages. [1] When Si 3 N 4 , [2] AlN, [3] AlN-Si 3 N 4 , [4] AlN-BN, [5] BN [6] were introduced into the SiO 2 matrix respectively, the resultant grain reinforced SiO 2 composites had the higher strength, fracture toughness than SiO 2 matrix. At the same time, the dielectric property was not influenced and the impact resistance was enhanced.The monolithic window materials, however, are susceptible to mechanical failure caused by shock wave loading at ultra high temperature, the destructive result is catastrophic. The continuous fiber reinforced ceramic matrix composites have received considerable attention for structural applications because of their excellent thermal stability, light weight, and damage tolerance imparted by the reinforcing fibers. In the field of the radar window materials the BN fibers and silica fibers are two common fibers reinforced ceramic matrix composites, such as BN f /SiO 2 [7] and BN f /(BN+SiO 2 ). [8] The fracture toughness of the composites was enhanced to a large degree. However, the fabrication of the continuous BN fibers is difficult and the fibers have not been manufactured on a large-scale. Silica fibers, with excellent ablative resistance, thermal shock damage resistance, dielectric properties, chemical stability and flexibility, are suitable for fabricating high temperature radar windows materials. [9][10][11] But the disadvantage of the silica fibers is that high temperature processing of typical inorganic systems will lead to serious fiber degradation. [11] Recently, three dimensional silica fibers reinforced Si 3 N 4 (3D SiO 2f /Si 3 N 4 ) ceramic composites have been prepared by Qi and his coworkers [12][13] through Preceramic polymer Impregnation Pyrolysis (PIP) methods at low temperature and the composites have good mechanical and dielectric properties while the ablation properties of the composites were not examined. In the present study, in order to fabricate a new radar window material for high-temperature application, the 2.5 dimensional silica fiber reinforced Si 3 N 4 -BN matrix composites were prepared by PIP method through repeated infiltration of hybrid precursor and pyrolysis at high temperature in ammonia atmosphere. The mechanical, microstructure, dielectric, thermal and ablation properties are characterized using a range of techniques and the results are discussed. Results and Discussion Densification of the compositesThe density of the samples as a function of pyrolysis cycles is plotted in Figure 1. Repeated infiltration pyrolysis cycles are required to densify the composites due to the shrinkage of precursor in firing. The ...

Ablation Property and Mechanism of Nitride‐Based Ceramic Composites Reinforced by Braided Silica Fibers

“…According to literature, [3] PBSZ was used to infiltrate 3-dimensional silica fiber fabric (3D SiO 2f ), the 3D-SiO 2f reinforced nitride-based composites (3D-SRNC) were prepared by PIP method. The silica fibers, produced by JingZhou Feilihua Silica Glass Corporation (China), have a diameter of 6 ∼ 8 lm, a density of 2.2 g/cm 3 , a room temperature tensile strength of 1 700 MPa and an elastic modulus of 78 GPa.…”

“…To form a 3D-braided silica fiber fabric, with the fiber volume fraction 50 %, those fabrics were woven by Beijing Fiberglass Research & Design Institute (China). The infiltration-curepyrolysis cycles were repeated for five times and then the density of the 3D-SRNC reaches 1.71 ∼ 1.74 g/cm 3 .…”

“…[18] However, for a radome or antenna window material, both of the ablation resistance and dielectric property must be considered, so a sublimation material will be better. In the work, the as-received composite are composed of Si 3 N 4 and BN, [3] both compounds have not the melting point. For example, Si 3 N 4 decomposes at 1900°C [13] and BN sublimates at 3000°C.…”

“…[2] So a radar window for a supersonic vehicle should process critical property, such as a high resistance to stress failure induced by large thermal load and a high ablation resistance. In our previous work, [3] the 2.5 dimensional silica fibers reinforced the nitride-based composites (2.5D SiO 2f /Si 3 N 4 -BN) were prepared by preceramic polymer impregnation and pyrolysis (PIP) method through repeated infiltration of hybrid precursor polyborosilazane (PBSZ). Results showed that the composites had an excellent mechanical, dielectric and ablation properties.…”

Polymer‐Derived SiBN Fiber for High‐Temperature Structural/Functional Applications

“…[11,12] Quartz fibers are one of the most commonly used reinforcements in radome composites because of their excellent dielectric properties. [13][14][15][16] However, their low mechanical property at high temperature is the critical drawback, limiting their application to more hostile conditions. [1,16,17] In addition, quartz fibers are intrinsically prone to crystallization at high temperatures, leading to the low preparation temperature of the composites.…”