新型液态聚碳硅烷前驱体制备碳化硅基超高温陶瓷及复合材料的研究

Advanced SiC based ultrahigh-temperature ceramics and composites are regarded as the materials of choice for sharp leading edges and nose tips of hypersonic vehicles, due to many advantages such as low density, high strength and good high temperature stability that they display. Moreover, SiC based ultrahigh-temperature powders are also key raw materials for matrix and surface oxidation and ablation resistance of Cf/SiC composites. To date, solid PCS had to infiltrate in the form of solution or fusion, which makes complicated procedures, high cost and low ceramic yield. On this account, we propose a new approach to prepare SiC based ultrahigh-temperature ceramics and composites using novel liquid polycarbosilane (LPCS). First, solid ultrahigh-temperature ceramic precursors dissolve directly into LPCS without extra solvent, forming liquid hybrid SiC based ultrahigh-temperature precursors, and their crosslinking and pyrolysis features are studied. Then, SiC based ultrahigh-temperature ceramics including powders and dense bulks, as well as composites are fabricated using the hybrid precursors, and their mechanical, oxidation and ablation properties are investigated, besides, the oxidation and ablation mechanisms are also given. Finally, the liquid hybrid precursors can be employed to manufacture light-weight SiC based porous ultrahigh-temperature ceramics for the first time, and their mechanical and contact damage tolerant ability are also evaluated.

先进SiC基超高温陶瓷及复合材料具有低密度、高强度和良好的高温稳定性等特点，成为高超声速飞行器翼前缘、鼻锥等部位防热构件的候选材料之一。SiC基超高温陶瓷粉体也是Cf/SiC等复合材料的基体和表面抗氧化、抗烧蚀涂层的关键原材料。针对目前PIP工艺中由于固态聚碳硅烷不能直接用于浸渍，需要采用溶液浸渍或熔融浸渍，从而导致工艺复杂、制造成本高以及陶瓷化产率低等问题，提出利用新型液态聚碳硅烷（LPCS）制备SiC基超高温陶瓷及复合材料。首先，拟将LPCS与固态超高温陶瓷前驱体在没有溶剂的情况下混合得到液态杂化SiC基超高温陶瓷前驱体，分析其交联裂解特性。然后，拟利用该前驱体制备SiC基超高温陶瓷（粉体、块体）及复合材料，研究其力学性能和抗氧化烧蚀性能，并阐明氧化和烧蚀机理。最后，拟利用该液态杂化前驱体通过模板复制法制备轻质SiC基多孔超高温陶瓷，并对其力学性能及抗接触损伤能力进行评价。

前驱体转化法制备超高温陶瓷及复合材料有着传统陶瓷工艺无法比拟的诸多优点。针对目前固态聚碳硅烷不能直接用于浸渍，需要采用溶液浸渍或熔融浸渍而导致的工艺复杂、制造成本高及陶瓷化产率低等问题，提出利用新型液态杂化聚碳硅烷（LPCS）前驱体转化制备SiC基超高温陶瓷及其复合材料，拓宽超高温陶瓷的应用。本项目的主要研究内容包括：（1）新型液态杂化SiC基超高温陶瓷前驱体的制备及其物性表征，将含锆聚合物或含铪聚合物在无需外加溶剂的条件下直接溶解到LPCS中，得到均相液态杂化SiC基超高温陶瓷前驱体，混杂前驱体的黏度和制备时间可通过改变各聚合物的比例进行调控，且该液态杂化前驱体具有高的陶瓷产率。（2）液态杂化陶瓷前驱体转化制备SiC基超高温陶瓷复合材料及性能研究，以液态杂化前驱体为原料，经过交联、裂解后得到SiC基复合陶瓷粉体，采用热压烧结得到SiC基超高温复相陶瓷，研究表明SiC基超高温陶瓷粉体结晶度高、粒径均匀、具有优异的抗氧化性能；而SiC基超高温复相陶瓷中两相分布均匀，且具有优异的力学性能。（3）碳纤维增强SiC基超高温复合材料的制备及性能研究，以液态杂化前驱体为原料，通过PIP工艺得到了二维穿刺碳纤维增强的SiC基复合材料，该复合材料具有较好的抗烧蚀性能，此外裂纹会通过在热解炭与陶瓷基体间形成的弱界面处发生偏转而使其拥有较高的力学性能。（4）生物形态的SiC基多孔超高温陶瓷的制备及性能研究，以碳化的木材为模板前驱体转化制备了轻质SiC基多孔超高温陶瓷，研究中通过优化制备工艺而使得轻质SiC基多孔陶瓷具有极高的力学性能和出色的抗接触损伤能力，可用于高温轻质结构部件。（5）静电纺丝结合前驱体热解制备SiC基复合陶瓷纤维的研究，以液态杂化前驱体为原料，通过静电纺丝技术在无需助纺剂的情况下得到复合陶瓷纤维前驱体，经交联、高温热解后得到了兼具连续均匀、直径可调控、比表面积大、拉伸强度高、耐高温特性好的SiC基陶瓷纤维，可作为模板制备纤维增强超高温复合材料。