Cheng Laifei

增强体含量对SiC W /SiC层状陶瓷复合材料强韧性的影响

采用流延-化学气相渗透（TC-CVI）工艺制备SiC晶须（SiC W ）/SiC层状陶瓷复合材料，研究了SiC W 含量对层状陶瓷复合材料力学性能和微观结构的影响，探讨了SiC W /SiC层状陶瓷复合材料的强韧化机制。结果表明：TC-CVI工艺能够有效提高复合材料中晶须含量（40vol%），减少制备过程对晶须损伤，所制备的SiC W /SiC层状陶瓷复合材料具有合适的层内及层间界面结合强度。随着SiC W 含量增加，层状陶瓷复合材料的密度和力学性能均有明显提高。含40vol%晶须的SiC W /SiC层状陶瓷复合材料的密度、弯曲强度和断裂韧性均比含25vol%晶须的分别提高了8.4%、30.8%和26.7%。断口形貌中能够观察到层间及层内的裂纹偏转，层内的裂纹桥接和晶须拔出等，这些为主要的增韧机制。高含量SiC W 及合适的层间和层内界面结合强度，对提高SiC W /SiC层状陶瓷复合材料强韧性有明显作用。

Effects of N on Electronic and Mechanical Properties of H-Type SiC

Structural, electronic and mechanical properties of the nH-SiC (n = 2, 4, 6, 8 and 10) polytypes are calculated by using the first-principles calculations based on the density-functional theory approach. The optimized lattice parameters of nH-SiC are in good agreement with the experimental data. The mechanical properties, including elastic constants, bulk modulus, Youngs modulus, shear modulus and Poissons ratio, are calculated. The analysis of elastic properties indicates that the effects of n on the mechanical properties of the five nH-SiC structures have no difference. The indirect band gap relationship for the five polytypes is Ebg2H > Ebg4H > Ebg6H > Ebg10H > Ebg8H.