反应熔渗制备高体积分数SiC纳米纤维增强SiC陶瓷基复合材料的界面设计及增强增韧机制研究

SiC ceramic fiber-reinforced SiC matrix composite materials (SiCf/SiC) is a key materials for the new high temperature structural parts. SiC ceramic fiber reinforcement is the key element for the SiCf/SiC matrix composites. Compared with the third-generation continuous SiC ceramic fiber with a tensile strength of 3 GPa, the single-crystal SiC nanowires/nanofibers have small diameter, high tensile strength (16GPa) and super-plasticity. The preform of SiC nanowire nonwoven fabric and nanowire paper/mat can be fabricated by this kinds of cotton-like SiC nanofibers. SiC nanofibers were regarded as the assistant reinforcement of the matrix composite materials, which was fabricated by the in situ synthesis method on the surface of SiC ceramic fiber or carbon fiber. Although the SiC nanowire-contained SiC ceramic shows stronger and tougher performance, it cannot shows the excellent mechanical properties of SiC nanofibers because the low volume fraction, low compactness of SiC nanofibres and uncontrollable interface. Based on our previous research work on the large-scale fabrication of SiC nanofibers and the reactive melt infiltration of SiC ceramic, the SiCnf/SiC matrix composite materials with high volume fraction and high compactness of SiC nanofibres will be fabricated by the reactive melt infiltration method. The reaction mechanism and kinetics of Si/C will be investigated. The interface between SiCnf and SiC matrix will be designed. The strengthening-toughening mechanisms of the high volume fraction SiC nanofibres reinforced SiC matrix composites will be discussed. SiCnf/SiC will provide a new strategy toward materials design and fabrication for the research and development of the SiC/SiC composites.

SiC陶瓷纤维增韧SiC陶瓷基复合材料(SiCf/SiC)是新一代高温热结构部件的关键材料。增强体SiC纤维是制备高质量SiCf/SiC的关键。与第三代SiC纤维（拉伸强度约3GPa）比较，单晶SiC纳米纤维（SiCnf）具有直径小、强度高（拉伸强度约16GPa）的特点，且宏观呈现棉花絮状，可加工为无纺布/纸/毡状预制体。目前SiCnf主要通过在SiC陶瓷纤维或碳纤维表面原位生长的方式，作为第二增强体引入到陶瓷基体中，虽然有一定强韧化效果，但存在SiCnf体积含量小、致密度低和界面难以调控的问题，无法有效发挥SiCnf优异的力学性能。申请人拟在前期SiCnf规模化制备和SiC陶瓷制备的基础之上，开展基于高体积分数、致密SiCnf增强SiC的反应熔渗制备及反应机理和动力学研究，SiCnf与SiC基体的界面设计，研究SiCnf强化机制。研究可为SiC/SiC制备提供新的研究途径和策略。

SiC纤维增强SiC陶瓷基复合材料(SiCf/SiC)是重要的高温热结构材料。与传统SiC陶瓷纤维增强体比较，单晶SiC纳米纤维（SiCnf）具有直径小、强度高的特点，且宏观呈现棉花絮状，可加工为无纺布/纸/毡状预制体。项目采用SiCnf为增强体，经模压成型、聚合物浸渍裂解和反应熔渗工艺制备了高体积分数、致密SiCnf/SiC。研究了PyC、BN和SiC多种基体-纤维界面涂层的制备，为降低高温渗硅过程对SiCnf的损伤并提高SiCnf对复合材料的增韧效果，通过PIP工艺对预制体分别进行了不同次数的裂解SiC填充和C/SiC、BN/SiC界面相包覆。分析了反应机理和动力学特征。优化熔渗工艺，实现了低孔隙率、低残余硅SiC陶瓷的制备，提高了复合材料的韧性，但存在复合材料抗弯强度较低。由于反应熔渗法制备SiCnf/SiC复合材料存在液硅相侵蚀性强，容易侵蚀界面层和纳米纤维，形成强的结合界面，制备的复合材料晶粒粗大。直径小的纳米纤维，在粗大的晶粒及硅相基体中，难以充分发挥其增韧效果。针对上述问题，提出了探索纳米浸渍瞬态共晶制备碳化硅纳米纤维增强纳米碳化硅陶瓷及其界面优化研究。同时研究还以超长碳化硅纳米纤维为原料，采用传统的手抄纸工艺制备了碳化硅纳米纤维纸。纳米纤维纸可折叠，可弯曲成管材、可以做无缝管，耐火性好，纤维交织、纯度高，可制作预浸带/片。实现了大尺寸SiC纳米纤维气凝胶的制备，气凝胶具有低密度、高孔隙率、低导热系数、耐高温和抗氧化等特性。研究结果将为新型SiC 纳米纤维增强增韧SiC陶瓷和高温热防护材料的研究与开发提供新材料设计思路和新制备技术。