原位自生碳纳米管增韧二硼化钛基陶瓷的韧化机制研究

The intrinsic low toughness of ceramics is still the shortcoming to limit the wider application of monolithic TiB2 material. In this study, fabrication of composites reinforced with CNTs grown in situ by CVD process can effectively solve the agglomeration problem of CNTs. High dense TiB2-based ceramics toughened by CNTs are sintered by SPS. Effects of the formation condition of CNTs and the sintering process of SPS on material properties are analyzed. In order to elucidate the toughening mechanism, the toughening effect of CNTs during crack propagation process is thoroughly investigated by numerical simulation and microanalysis. Combined with finite element model, the thermal shock behavior of TiB2-based ceramics toughened by CNTs is investigated by quenching test to understand the thermal shock mechanism. The investigation presented here will enrich the design theory of ceramic composites for high temperature structural applications and point out a promising way for improving the mechanical properties of TiB2-based ultra-high temperature ceramics. It also gives a theoretical basis to advance the practical course of the predicting for safety use in advanced thermal protection systems.

二硼化钛（TiB2）作为超高温结构陶瓷材料，本征脆性是制约它实际应用的关键因素。本课题拟通过化学气相沉积法在二硼化钛基体粉料中原位生长出均匀分散的碳纳米管（CNTs），采用放电等离子烧结（SPS）技术制备CNTs/TiB2复合材料，以有效地解决碳纳米管易团聚的问题而实现增韧效果；系统地考察CNTs的生成条件、SPS烧结工艺参数对材料性能的影响规律，通过断裂力学模型数值模拟和微观分析等方法弄清裂纹扩展过程中CNTs的作用，阐明CNTs的韧化机制；建立复合材料热震过程的有限元模型，并结合水淬–残余强度法考察CNTs/TiB2复合材料的抗热震性能，厘清其抗热震机理。它将丰富超高温结构陶瓷材料的制备方法，为开发高性能的二硼化钛基超高温结构陶瓷材料，推进其在高超声速飞行器结构部件的实用化进程，提供理论依据。

二硼化钛（TiB2）由于具有高熔点、高强度、高硬度以及优秀的化学稳定性等优点，成为高温结构材料的优秀候选材料。但是同其他陶瓷一样本征脆性仍是制约它实际应用的关键因素。本项目采用了化学气相沉积法在二硼化钛基体粉料中原位生长出均匀分散的碳纳米管（CNTs），并结合放电等离子烧结（SPS）技术制备了CNTs/TiB2复合材料，成功地获得了均匀分散的CNTs增韧TiB2基复合材料；系统地考察了CNTs的生成条件、SPS烧结工艺参数对材料性能的影响规律，最终获得的CNTs/TiB2基复合材料具有优秀的室温力学性能，断裂韧性达到15.9MPa·m1/2；通过断裂力学模型数值模拟和微观分析等方法厘清了裂纹扩展过程中CNTs的作用，阐明了韧化机制主要有裂纹偏转、裂纹桥联、CNTs脱粘以及拔出增韧；建立了复合材料热震过程的有限元模型，并结合水淬–残余强度法考察了CNTs/TiB2复合材料的抗热震性能，厘清了抗热震机理。研究结果丰富了复合材料的制备方法，为开发高性能的二硼化钛基复合材料，推进其在高超声速飞行器结构部件的实用化进程，提供了理论依据。