Ablation behavior of microwave absorbing SiCf/Si3N4 composites containing ZrOC-SiCN - SiCN matrix

The thermal protection materials of ultra-high speed aircraft need the stealth performance, and it require the microwave absorbing materials should have high ablation resistance to serve under extreme conditions (>2000 degrees C). In this work, amorphous ZrOC-SiCN and SiCN were introduced into the inter-bundle matrix of SiC fiber reinforced Si3N4 matrix composites to improve the ablation resistance while retaining the wave-absorbing properties. For SiCf/Si3N4, the SiC nanocrystallines in SiC fiber are oxidized into SiO2 and accumulate on the surface, and the Si3N4 matrix is first transformed into SiC grains and then the SiC grains are gradually ablated into spherical SiO2 in the ablation process. After the introduction of ZrOC-SiCN and heat-treated at 1500 degrees C, the ZrCN can be formed to increase the scouring resistance of each woven layer, and the oxide film with high viscosity also can be formed, preventing the fiber bundles from being blown away in the central region, leading to the decrease of mass and line ablation rate from 12.2 mg/s and 27.3 mu m/s to 7.3 mg/s and 16 mu m/s, respectively. Meanwhile, the minimum reflection coefficient of the composite decreases from -4.9 to -10.6 dB.