MWCNTs增强增韧SiBCN陶瓷力学及抗氧化性能研究

SiBCN ceramics have found great potential applications in the area of aeronautics and astronautics due to their excellent thermal resistance and oxidation resistance. However, the brittle failure and low thermal shock resistance have limited their practical applications. In this project, multi-walled carbon nanotubes (MWCNTs) were employed to toughen and strengthen the SiBCN ceramics. Firstly, MWCNTs are good enhancements attribute to their excellent mechanical properties. On the other hand, nanosized SiC and BN(C) can be formed owing to the high reaction activity of MWCNTs, where the SiC and BN(C) could enhance the ceramics and improve the oxidation resistance. The present work will investigate the mechanisms for the structure transformation of MWCNTs into SiC whiskers and BN(C) nanowires. Furthermore, the phases interfacial structure together with strengthening and toughening mechanisms will be considered to reveal the intrinsic relationship between composition, microstructure and properties. Besides, the synergistic antioxidant mechanisms of the nano SiC coated MWCNTs together with SiC and BN(C) will be discussed. All the above works will provide theoretical and technical supports for processing of high performance SiBCN ceramics, which have important academic value and potential engineering application prospects.

SiBCN陶瓷具有耐高温，抗氧化等优点，尤其在航空航天领域具有广泛的应用前景。但是材料自身的断裂韧性和抗热震性还不能完全满足使用需求。本项目拟采用多壁碳纳米管增强增韧SiBCN陶瓷。首先，多壁碳纳米管具有优异的力学性能，在改善SiBCN陶瓷的断裂韧性方面具有很好的应用潜力；其次，多壁碳纳米管高的反应活性还有利于形成碳化硅（SiC）和硼氮碳（BN(C)）纳米晶粒，提高材料的力学性能和抗氧化性。本项目首先研究SiBCN陶瓷材料中碳纳米管向SiC以及BN(C)纳米线的结构演变；进而研究各相界面结构，揭示多壁碳纳米管以及纳米SiC和BN(C)陶瓷相的增强增韧机理；最后，采用纳米SiC涂层MWCNTs的方式进一步提高SiBCN陶瓷的抗氧化性，并阐明SiC涂层多壁碳纳米管、纳米SiC晶粒及BN(C)湍层结构的协同抗氧化机理，为制备优异SiBCN陶瓷提供理论与实验指导，具有重要的学术价值和工程应用前景。

主要研究了多壁碳纳米管（MWCNTs）以及SiC涂覆MWCNTs与Si2BC3N陶瓷基体间的界面结合状态，探讨了其强韧化机理；研究了金属Zr-Al复合添加剂对Si2BC3N陶瓷材料基体致密化和表面氧化层物相组成对抗氧化性的作用机理；研究直接引入超高温组元（ZrB2）提高Si2BC3N基陶瓷复合材料耐烧蚀性，并探讨其作用机理。为制备优异SiBCN陶瓷提供理论与实验指导，具有重要的学术价值和工程应用前景。通过开展上述研究工作，得到如下主要结论：.（1）引入1 vol.% MWCNTs的Si2BC3N基陶瓷复合材料抗弯强度和断裂韧性分别达到462.1 MPa和5.54 MPa·m1/2。对比而言，2 vol.% SiC涂覆MWCNTs增强Si2BC3N基陶瓷复合材料的抗弯强度和断裂韧性分别达到532.1 MPa和6.66 MPa·m1/2。从而，上述改性Si2BC3N基陶瓷抗热震性得到显著提高。MWCNTs的强韧化机理为“裂纹桥接”，“MWCNTs拔出”以及“裂纹偏转”。.（2）Zr-Al添加可促进Si2BC3N基陶瓷复合材料致密化和力学性能提高。1 mol% Zr-Al添加试样的抗弯强度和断裂韧性分别达到590.2 MPa和4.93 MPa·m1/2。上述强度和断裂韧性的提高正是由于材料中SiC和BN(C)结构的发育以及材料的致密化提高以及纳米氧化物/团聚体的钉扎作用。此外，1 mol% Zr-Al添加的Si2BC3N基陶瓷复合材料具有优化的抗热震性和抗氧化性。.（3）含有10 wt.%和20 wt.% ZrB2的Si2BC3N基陶瓷复合材料的抗弯强度和断裂韧性显著提高，分别达到559.6 MPa、6.71 MPa·m1/2和512.3 MPa、6.77 MPa·m1/2。添加10 wt.% ZrB2试样在1000 ℃热震后仍保持363.6 MPa的残余强度。引入10 wt.%和20 wt.% ZrB2试样的线烧蚀率由0.047mm/s分别降低至0.009 mm/s和0.007mm/s；质量烧蚀率由20.796 mg/s分别降低至1.908和2.095 mg/s。