Abstract
SiBN fibers are one of the most admirable microwave-transparent reinforced materials for high Mach number aircrafts. Currently, the detailed high-temperature oxidation behavior of SiBN fibers has not been studied yet. In this work, we studied the high-temperature oxidation behavior of SiBN fibers with different boron contents at the temperature range of 1000–1400 °C in air. SiBN fibers started to be oxidized at 1100 °C, with Si3N4 and BN phase oxidized to SiO2 and B2O3, respectively. Due to the gasification and the escape of molten B2O3 at high temperatures, amorphous SiO2 could be remained at the fiber surface. As the fiber further oxidized, the molten B2O3 at the inside may infiltrate into the fiber interior to react with Si3N4, causing the precipitation of hexagonal boron nitride (h-BN) nanoparticles and the formation of SiO2/BN layer. Finally, complex oxidation layers with two distinct concentric sublayers accompanied with two transition sublayers could be formed after the oxidizing treatment.
Highlights
With the flight speed of aircrafts increasing to a higher Mach number, the aerodynamic heating effect could be more drastic, which caused a huge challenge to the thermal protection of the components in hot end, especially for the radomes that used as the communication windows [1,2]
J Adv Ceram 2021, 10(4): 768–777 related to the high-temperature properties of SiBN fibers are still lacking, especially for their oxidation resistance at high temperatures, which is very important for their actual applications in reinforcing the microwave-transparent composites (MTCs) that used in high-temperature oxidation atmosphere
Whereas SNB-5 and SNB-7 fibers showed a rather lower surface roughness (Ra) of 3.25 and 1.85 nm, respectively. These results mean that SiBN fibers with a higher boron content showed a rather smooth surface, which may be attributed to the higher ceramic yield of pre-ceramic precursors that used to prepare these SiBN fibers
Summary
With the flight speed of aircrafts increasing to a higher Mach number, the aerodynamic heating effect could be more drastic, which caused a huge challenge to the thermal protection of the components in hot end, especially for the radomes that used as the communication windows [1,2]. The preparation of high-quality SiBN fibers is still a huge challenge due to the complex fabrication process and high sensitivity of precursor [12,13]. Cinibulk and Parthasarathy [15] investigated the oxidation behavior of SiBCN fibers They observed the complex sublayers with three distinct concentric layers, each increasing in oxygen concentration from the core to the outer surface. SiBN fibers showed different chemical composition from Si3N4 fibers and SiBCN fibers, should present different oxidation behavior and oxidation layer microstructures. The obtained SiBN fibers showed excellent high-temperature stability up to 1600 °C in an inert atmosphere. In this work, these SiBN fibers with different boron contents were treated in the temperature range of 1000– 1400 °C in air. The oxidation behavior as well as the microstructural evolution and mechanical properties of the SiBN fibers have been discussed through the whole paper
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