The Atomic Simulation Of PyC Interphase Of C/Sic Composite

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.