BN纤维晶体形态及显微结构的研究

Study on the Crystallinity and Microstructural Ordering in Boron Nitride Fibers

纤维的结构是由无定形区域和纳米尺寸的晶粒沿轴向排列宽区域组成的无定形的晶体结构会造成纤维的低模量;相反,较大的晶粒,以六方结构的形式沿纤维的轴向排列会使纤维具有高模量。当结晶度提高时,外力破坏引起的纤维断裂缺陷很容易扩张,导致纤维断裂。由于纤维多孔和存在的缺陷使强度与微观结构的关系变的模糊不清。本文利用X-衍射和显微镜技术,对不同试验得到的力学性能各异BN纤维进行定性和定量测试,得到的结论是纤维的弹性模量是由晶体的取向决定的。

Young＇s modulus was controlled by grain orientation. The disordered microstructure of low modulus fibers consisted of amorphous regions and nanometer- sized crystallites arranged in a wide range of orientation. In contrast, high modulus samples showed a coarse-grained microtexture in which crystallites were ordered in a mesohexagonal arrangement along the fiber-axis. Cracks were easily propagated as crystallinity increased, leading to decreased failure strain. The strength-microstructure relationship was obscured by the fiber porosity and defects. Alitative and quantitative analysis of the microtexture/ microstructure in several experimental boron nitride fibers was investigated by X-ray diffraction and electron microscopy according to their mechanical properties.