Preparation and Oxidation Behaviors of C/SiC-BN Composites

doi:10.15541/jim20230583

Abstract

Abstract:

As thermal structural materials operating at high temperatures, C/SiC composites have extensive applications as thermal protection systems in aerospace vehicles. However, their limited antioxidant performance at low and medium temperatures restricts their utilization in diverse fields. In this work, an improved slurry impregnation technique was employed to introduce antioxidant component BN at different contents into the carbon fiber felts by adjusting the ceramic content in the slurry, and then densified the felts to prepare C/SiC-BN composites using reaction melt infiltration method. Effects of BN content on the composition, microstructure and oxidation behaviors of the composites were systematically studied, and relevant oxidation mechanisms were explored. Experimental results indicate that introduction of BN particles significantly reduces the open porosity of C/SiC and enhances the initial oxidation temperature of C/SiC. The C/SiC-BN composite with 3% BN (mass fraction, sample B3) has optimal antioxidant performance, and the corresponding mass loss rates in static air at 900, 1200 and 1500 ℃ for 1 h are 0.009%, -0.301%, and -0.596%, respectively. After oxidation at 1500 ℃, the strength retention rate of sample B3 is up to 52%. At 900 ℃, the mass change is dominated by slow weight loss controlled by O₂diffusion and oxidation of C and BN. At 1200 ℃, the oxidation rates of C and BN phases increase while SiC begins to undergo significant oxidation. New formed oxidation products, such as B₂O₃, borosilicate and SiO₂, gradually slow the diffusion of O₂and reduce the damage of carbon. At 1500 ℃, the oxidation rate of SiC is accelerated obviously. Finally, a continuous oxidation film formed by generated SiO₂ retards the inward diffusion of O₂, and overflow of gas products (such as B₂O₃ and CO) and continuous formation of SiO₂ dominate the oxidation process.

Key words: slurry impregnation, C/SiC, BN, microstructure, oxidation behavior

CLC Number:

TB332

JIANG Lingyi, PANG Shengyang, YANG Chao, ZHANG Yue, HU Chenglong, TANG Sufang. Preparation and Oxidation Behaviors of C/SiC-BN Composites[J]. Journal of Inorganic Materials, 2024, 39(7): 779-786.

Figures/Tables 11

Fig. 1 Schematic preparation process of C/SiC-BN composites

Fig. 2 SEM images of low-density C/C preforms after slurry impregnation with BN (a) Sample B1; (b) Sample B3; (c) Sample B5; (d) Enlarged image of sample B5

Fig. 3 Cross-sectional morphologies of C/SiC and C/SiC-BN composites and their magnification images (a, b) Sample B0; (c, d) Sample B5

Table 1 Densities and porosities of C/SiC and C/SiC-BN composites

Sample	Density/(g·cm^-3)	Porosity/%
B0	2.29	8.5
B1	2.37	5.6
B3	2.34	6.3
B5	2.37	6.7

Fig. 4 Oxidation weight loss curves of C/SiC and C/SiC-BN oxidated at different temperatures (a) 900 ℃; (b) 1200 ℃; (c) 1500 ℃

Fig. 5 TG-DSC curves of composites with different BN contents Colorful figure is available on website

Fig. 6 Surface morphologies of C/SiC-BN(B3) after oxidation at different temperatures for 1 h (a) 900 ℃; (b) 1200 ℃; (c) 1500 ℃

Table 2 Flexural strength and modulus of C/SiC-BN composites before and after oxidation

Sample	Flexural strength/MPa	Strength after oxidation/MPa	Strength retention rate/%	Modulus/GPa
B1	172	70	41	18.2
B3	198	103	52	19.3
B5	181	78	43	17.3

Fig. 7 XRD patterns of the surface of C/SiC-BN(B3) after oxidation at different temperatures

Fig. 8 Cross-sectional morphologies of C/SiC-BN(B3) after oxidation at different temperatures for 1 h (a) 900 ℃; (b) 1200 ℃; (c) 1500 ℃

Fig. 9 Vapor pressure-temperature curves of B2O3 and SiO2

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