B_(4)C改性SiC/SiC复合材料自愈合机理研究

Crack Healing Mechanism of B_(4)C Modified SiC/SiC Composites

采用预浸料–熔渗工艺制备了B_(4)C改性SiC/SiC复合材料(SiC/SiC–B_(4)C复合材料),研究了SiC–B_(4)C改性基体在700℃、1000℃、1200℃、1350℃下氧化50 h的本征氧化行为及自愈合规律,有效观察到了基体的自愈合行为,同时考察了SiC/SiC–B_(4)C复合材料的抗氧化性能,通过材料重量变化和强度保持率衡量其在氧化环境中的损伤程度,揭示了氧化行为。研究结果表明,氧化初期B_(4)C开始发生氧化反应,此时的液态自愈合相主要成分为B_(2)O_(3)。随着温度的升高,氧化生成的SiO_(2)将与B_(2)O_(3)结合生成硅硼玻璃相,当温度进一步升高至1350℃时,由于硅硼玻璃分解加剧,导致自愈合效果减弱。此外,高温导致的硅硼玻璃黏度下降也将有利于氧化介质扩散。SiC/SiC–B_(4)C复合材料在1200℃氧化50 h后仍保持较好的力学性能,说明B_(4)C氧化后生成的B_(2)O_(3)、SiO_(2)等黏流态物质可以在一定程度上封填裂纹,赋予材料高温下自愈合机制。

B_(4)C induced SiC/SiC composites were prepared by prepreg-melt infiltration method.Oxidation behavior and self-healing mechanisms of B_(4)C modified SiC matrix was studied at different oxidized temperatures.Self-healing behavior of the SiC-B_(4)C matrix has also been noticed,cracks were filled by the oxidation products at the high temperatures.Moreover,the oxidation resistance of the SiC/SiC-B_(4)C composites at elevated temperature was also investigated.The results demonstrate that when the oxidation temperature is 700℃,B_(2)O_(3)glasses are formed on the surface of ceramic by B_(4)C oxides.B_(2)O_(3)is observed as the major phase in SiC matrix.With the temperature increasing,SiO_(2)phases are formed,and combined with B_(2)O_(3)phases to form the liquid borosilicate glass.When the temperature rises to 1200℃,the borosilicate glass will decomposes into SiO_(2)and gaseous B_(2)O_(3).At 1350℃,the content of B_(2)O_(3)decreases rapidly for borosilicate glass decomposing into B_(2)O_(3)which volatilizes itself.On the other hand,high temperature will cause the viscosity of borosilicate glass to decrease,hence,accelerates the oxygen diffusion.SiC/SiC-B_(4)C composites retain great mechanical properties at 1200℃for 50 h.The main mechanisms are that borosilicate glass oxidized from B_(4)C can heal cracks in the composites effectively.