C/SiC-BN复合材料的制备及氧化行为

Preparation and Oxidation Behaviors of C/SiC-BN Composites

C/SiC复合材料作为一种高温结构材料,在航空航天热防护领域具有广泛的应用前景。然而,该材料的中低温抗氧化性能相对较差,制约了其在更广泛领域的应用。本研究采用料浆抽滤工艺,通过调节料浆中陶瓷含量在纤维增强体中引入不同含量的抗氧化组元BN,再通过反应熔体渗透法制备C/SiC-BN复合材料。系统研究了不同BN含量对复合材料结构组成及抗氧化行为的影响,并分析相关氧化机理。研究结果表明:引入BN颗粒显著降低了C/SiC的开口孔隙率,并明显提高了C/SiC的起始氧化温度。引入质量分数3%BN时,C/SiC-BN复合材料(B3样品)的抗氧化性能最优,其在900、1200和1500℃静态氧化1 h的质量损失率分别为0.009%、–0.301%、–0.596%,显著优于C/SiC。1500℃氧化后,B3样品的强度保持率最高,达到52%。900℃氧化时,C/SiC-BN复合材料主要经历C相和BN相的氧化,以O_(2)扩散反应控制的缓慢失重为主;1200℃氧化时,C相和BN相氧化速率加快,SiC发显著氧化,生成的B_(2)O_(3)、硼硅酸盐和SiO_(2)等氧化产物减缓了O_(2)的扩散速率,减小了基体碳的损伤;1500℃氧化时,SiC氧化速率加快,生成的SiO_(2)在复合材料表面形成的连续氧化膜阻碍了O_(2)的向内扩散。B_(2)O_(3)、CO等气体产物溢出及持续生成SiO_(2)主导了整个氧化过程。

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 B_(3) is up to 52%.At 900℃,the mass change is dominated by slow weight loss controlled by O_(2)diffusion 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 B_(2)O_(3),borosilicate and SiO_(2),gradually slow the diffusion of O_(2)and reduce the damage of carbon.At 1500℃,the oxidation rate of SiC is accelerated obviously.Finally,a continuous oxidation film formed by generated SiO_(2)retards the inward diffusion of O_(2),and overflow of gas products(such as B_(2)O_(3)and CO)and continuous formation of SiO_(2)dominate the oxidation process.