【作者】 叶雅静；

【导师】 张立同；

【作者基本信息】 西北工业大学 ， 材料学， 2003， 硕士

【摘要】 材料设计的计算机模拟近二十年来发展较快，所形成的计算材料学已逐渐发展成为一门学科。材料设计分为宏观、细观(介观)和微观三个层次，其中，微观的原子级模拟已成为弥补实验不足、探索微观世界的一种重要方法。本文正是用原子级模拟的一些方法，如分子力学、分子动力学等，借助Cerius~2材料设计软件来研究C／SiC复合材料热解碳界面相区域的微结构及性能演变，及其对复合材料整体力学性能及环境性能的影响。主要研究内容和结果如下： 1．根据前处理C／SiC复合材料的断裂韧性和弯曲强度比未处理的提高了30～50％的结果，用分子动力学方法研究前处理过程对界面相微观结构和力学性能的影响。分子动力学模拟结果表明，(1)界面相内部无定形碳部分微结构无明显变化，石墨片层部分沿纤维轴向滑移；(2)界面相模量发生变化，界面相区域各部分的体积弹性模量降低，无定形碳部分及石墨片层部分垂直于纤维轴向的杨氏模量降低，平行于纤维轴向的杨氏模量升高。微结构和模量的变化使得沉积SiC后复合材料的断裂韧性和三点弯曲强度提高，纤维和界面相结合减弱，有利于裂纹扩展。 2．首次用热力学计算和分子动力学方法研究了PyC界面相注入B离子对C／SiC复合材料抗氧化性及抗腐蚀性能的影响。预测了B离子注入PyC界面相后，经高温处理生成的碳化硼能够和氧、硫酸钠反应生成氧化硼。氧化硼在其挥发温度(1273K)以下能够有效阻挡氧及部分硫酸钠蒸汽的进一步扩散，从而保护了纤维。而在1273K以上氧化硼挥发，丧失了对界面相的保护作用。 3．提出将协同学的思想用于原子级模拟及跨尺度模拟的思路，并在此基础上，提出下一步的工作设想：(1)分析热处理前后界面相区域应力-应变曲线的变化；(2)航空发动机模拟环境中，氧、硫酸钠蒸汽及水蒸汽耦合效应对界面相抗氧化性、抗腐蚀性的影响；(3)1273K以上界面相环境性能提高的方法。更多还原

【Abstract】 Materials design by computer simulation develops quickly in near 20 years. Computation materials science has gradually developed into a subject. Materials design has been divided into three scale levels: macro scale method, meso scale method and micro scale method. Among these three methods, atomic simulation has become an important method to cover shortages of experiment and explore microscopic world. In this paper, the methods of atomic simulation, such as molecular mechanics (MM) and molecular dynamics (MD), have been used to study the evolvement of microstructure and properties of PyC interphase of C/SiC composite. The influences of the evolvement on the mechanism properties and environment properties of C/SiC composite have been investigated also via the use of Cerius soft package. The main contents and conclusions investigated are as follows:1. The fracture toughness and bending strength of C/SiC composite were improved notably after the pre-treatment of Cp/Ci at 2073K. On the basis of the above phenomenon, the effect of pre-treatment on interphase microstructure and mechanical properties of C/SiC composites was investigated by MD simulation. The result of MD simulation means that: (1) the microstructure in the amorphous carbon has no obvious change, the slippage which is parallel to the fiber axes in the graphite slices of the PyC interphase was found; (2) bulk moduli of every part of interphase diminished, Young’s moduli in all three direction of amorphous carbon diminished, Young’s moduli of the graphite slices in the direction of parallel to the fiber radial decreased, and ones in the direction of parallel to the fiber axes increased. The changes of microstructure and moduli caused the increasing of fracture toughness and three point bending strength of C/SiC and the weakly bonding between fiber and interphase, which is helpful to the crack expansion.2. Thermodynamics and MD methods were used to study the mechanism ofoxidation and corrosion resistance of PyC interphase by implanting B ion. Implanted B ion in the PyC interphase came into being B4C, and reacted with oxygen and sodium sulfate producing B2O3. B2O3 could barrier the diffusion of O2 and Na2SO4 steam into interphase downwards of 1273K of volatilization temperature of B2O3. Upwards of 1273K, B2O3 will volatilize gradually and lose the protection to the interphase.3. Bring forward a new idea: the ideology of synergetics used in atomic simulation and multi-scale simulation of materials design. On the basis of this, next tasks were put forward: (1) analyzing the changes of stress-strain curves of the interphase before and after pre-treatment; (2) the efficient of the coupling effect of O2, Na2S04 and H2O stream on the oxidation and erosion resistance of interphase; (3) the methods of improving environment performance of interphase above 1273K.更多还原