B4C纳米线／Al2O3基纳米复合材料的微观力学及其断裂韧性评价

Could ceramics be toughened by one-dimensional nanomaterials and to what degree the toughening by fiber bridging across the crack wake in fiber-reinforced composite contribute to the toughening with carbon nanotubes, these are questions that need to be answered. In situ observation techniques under low loading rate is used to study the fracture behavior of carbon nanotube/ceramic matrix nanocompositesc, the results confirm that carbon nanotubes can play a role of bridging toughening ceramic matrix. However, the layered structure of carbon nanotubes leads to the complexity of the interface, along with the thermal expansion mismatch between carbon nanotubes and ceramcs, limit carbon nanotubes’ toughening effect. B4C nanowires with a structure is close to conventional fibers and a thermal expansion coefficient close to Al2O3, has a great potential to improve the fracture toughness of ceramics. In this project, B4C nanowires are introduced into the Al2O3 ceramic matrix as the second phase, and the toughening mechanism and toughening effect of one-dimensional nanomaterials on the ceramic matrix are studied. By means of in situ observation, constitutive relation of bridging crack cohesive stress and crack opening displacement will be built to discuss the micromechanics of nanocomposites. It has important academic significance and application value for the relationship between the composition, microstructure and properties of toughening mechanism understanding of one-dimensional nanomaterials and composites.

一维纳米材料等能否起到增韧陶瓷基体的作用，传统的纤维桥联增韧机理在多大程度上适用于一维纳米材料，有待深入研究。低加载速度下的原位观测手段被用来研究碳纳米管/陶瓷基纳米复合材料的断裂行为，证明了碳纳米管确实能起到桥联增韧陶瓷基体的作用，但其层状结构导致的界面结构复杂性以及碳纳米管/陶瓷基体间的热胀失配，限制了碳纳米管的增韧效果。B4C纳米线的实心结构与传统纤维相似，热膨胀系数与Al2O3接近，将其加入纳米Al2O3陶瓷基体中，界面结构简单可控，在改善材料断裂韧性方面具有巨大的潜力。本项目将B4C纳米线作为第二相引入纳米Al2O3陶瓷基体中，开展关于一维纳米材料对陶瓷基体的增韧机制和增韧效应的研究。结合原位观测手段建立桥联裂纹的内聚应力和裂纹张开位移之间的本构关系来分析裂纹扩展中的微观力学，对于认识一维纳米材料的增韧机理与复合材料的组成、显微结构和性能的关系具有具有重要的学术意义和应用价值。

本项目研究了不同B源、C源以及原料配比，催化剂种类和比例，Ar气氛的流量，坩埚的形状和尺寸，原料在坩埚中的位置以及铺排方式对B4C纳米线的产量以及形貌均匀度的影响，完善了B4C纳米线的制备工艺。利用杂凝聚方法得到均匀分散的B4C纳米线/Al2O3纳米复合粉体；利用SPS对制备的一系列不同含量的B4C纳米线/Al2O3纳米复合粉体进行了烧结，对于烧结工艺进行了探索，在1300C温度下制备了一系列不同组分的致密B4C纳米线/Al2O3纳米复合陶瓷样品。研制了原位观测的双悬臂梁法测试用夹具和三点弯曲测试用夹具；加工了用于原位观测的样品，并利用硬度仪在样品表面预制了微裂纹；在GatanMtest2000拉伸／压缩台上以较低的加载速率（0.033-50μm/s）原位观察纳米复合材料的断裂行为，测量了裂纹位移与应力曲线。对深入探讨一维纳米材料对陶瓷基体的增韧效应和增韧机制具有重要的研究价值。采用改进的气-液-固（VLS）法合成的B4C纳米线因为含有丰富的堆叠层错缺陷而表现出不错的微波吸收性能。通过多步VLS过程将SiC纳米颗粒引入到B4C纳米线中，实现了B4C纳米线的异质界面工程。SiC/B4C杂化纳米线的低反射损耗值和宽吸收带宽，以及高温稳定性和轻质性使其成为恶劣环境下高效电磁波吸收剂的良好候选材料。