透明Al2O3基连续纤维的纳米晶定向互锁结构制备及其强韧化机制

Alumina-based continuous fibers are used as high temperature structural materials in aerobic environment. Aiming at the problem of strength and toughness insufficient caused by equiaxed grain, the strength and toughness of fiber can be improved greatly through the microstructure tailoring about a oriented interlocking structure of the elongated grain, and combining with the size effect of macroscopic fiber diameter and microscopic nanocrystalline grain under multiple scales.This project intends to use liquid catalyst method to prepare ultrafine nanometer mullite whisker, take it as template seed, and obtain the gel fiber which contain oriented whiskers along with the axial direction through dry spinning process. Furthermore, the dense alumina-based continuous fibers with nanometer elongated grains oriented structure were obtained by vacuum rapid sintering.The influence of size and morphology of mullite whisker template as well as the adding amount on fiber density and microstructure were studied systematically. The oriented mechanism of fiber matrix grain under the guidance of whisker template after its anisotropic growth was illuminated. The synergistic mechanism of fiber densification and ultrafine nanocrystals during rapid sintering was revealed. The effects of microstructure characteristics such as the size and distribution of elongated grains on macroscopic mechanical/optical properties were studied. Combined with the size effect, the toughening mechanism and optical properties under multiscale of fiber diameter and nanocrystalline were revealed. It provides a new method for innovative design and functionalization of ceramic fiber.

氧化铝基连续纤维作为有氧环境用高温结构材料的增强补韧体，在航空航天领域可发挥重要作用。针对等轴晶粒导致其强韧性不足的问题，通过棒状晶定向互锁结构设计，结合多尺度下宏观纤维直径和微观纳米晶粒的尺寸效应，可大幅改善纤维的强韧性。本项目拟利用液态催化剂法制备超细直径纳米莫来石晶须,以其为模板籽晶，通过干法纺丝获得籽晶沿轴向定向排布的凝胶纤维；进一步通过真空快速烧结，获得具有纳米尺度的棒状晶粒定向排布结构的致密氧化铝基连续纤维。系统研究莫来石晶须模板籽晶的尺寸和形态、以及添加量对纤维致密度和微观结构的影响规律；阐明籽晶诱导纤维基体晶粒各向异性生长进而定向的生长机制；揭示快速烧结过程中纤维致密化和超细纳米晶粒的协同调控机理；研究纤维棒状晶粒尺寸及分布等内在特征对宏观力学/光学性能的影响规律；结合尺寸效应，揭示多尺度下纤维直径和纳米晶的强韧化机制和光学特性；为陶瓷纤维的创新设计和功能化提供了新思路。

氧化铝基连续纤维作为有氧环境用高温结构材料的增强补韧体，在航空航天领域可发挥重要作用。项目针对等轴晶粒导致其强韧性不足的问题，通过棒状晶定向互锁结构设计，结合多尺度下宏观纤维直径和微观纳米晶粒的尺寸效应，大幅改善纤维的强韧性项目利用液态催化剂HF制备超细直径纳米莫来石晶须,以其为模板籽晶，通过干法纺丝获得籽晶沿轴向定向排布的凝胶纤维；进一步通过真空快速烧结，获得具有纳米尺度的棒状晶粒定向排布结构的致密氧化铝基连续纤维。系统研究莫来石晶须模板籽晶的尺寸和形态、以及添加量对纤维致密度和微观结构的影响规律；阐明籽晶诱导纤维基体晶粒各向异性生长进而定向的生长机制；结合尺寸效应，揭示多尺度下纤维直径和纳米晶的强韧化机制。研究表明，在莫来石晶须籽晶制备时，催化剂液态氢氟酸在室温溶胶阶段就通过与铝源发生反应式，以Al-F成键的形式留存在体系中，进而通过中间产物黄玉相的分解实现莫来石化转变，且黄玉相在900℃以下就会出现；莫来石籽晶在氧化铝和莫来石相变的过程中，通过升高氧化铝的相变温度，完成了对组织定向的诱导，当烧结温度低于1400 ℃时氧化铝纤维组织为等轴晶，1400 ℃以上开始形成棒状晶，1550 ℃时纤维中基体组织完成棒状定向，于此过程相对应，氧化铝相的含量从1400℃时的14%上升到了21%，而莫来石相含量由84%下降到了79%。最终获得了与纤维轴向统计夹角小于30º的棒状定向纤维，确定了莫来石晶须籽晶的最佳添加量为5 wt%，并且使纤维的制备温度升高到1500℃以上。本项目为陶瓷纤维的创新设计和功能化提供了新思路。