SiC晶须及原位增强Si_3N_4基复合材料的断裂过程

FRACTURE PROCESS OF SiC_WHISKER_REINFORCED AND IN_SITU REINFORCED Si 3N 4 COMPOSITES

探讨了ＳｉＣ晶须增强和β－ｓｉａｌｏｎ细长晶粒原位增强Ｓｉ３Ｎ４基复合材料的断裂过程．２种材料的试验结果都显示出明显的二级增韧行为：一级增韧过程，断裂阻抗ＫＲ随微小的裂纹扩展而急剧增大，在裂纹扩展到大约０．２５ｍｍ时达到饱和；二级增韧过程，ＫＲ缓慢增长，一直持续到裂纹扩展达到１ｍｍ（原位增强）和１．８ｍｍ（晶须增强）．观察和分析表明：二级增韧行为的发生，本质上起因于裂纹尖端后方桥接晶须和细长晶粒与基体之间界面的后续解离，这些增强相与裂纹面法线之间方位角的存在是诱发后续解离的支配性原因．

Fracture resistance process of SiC_whisker_reinforced and in_situ reinforced Si 3N 4 composites was explored. The experimental results of both the materials show considerable two_step toughening behavior. In the first toughening process, the fracture resistance K R increases quickly with crack extension, and becomes constant when the crack extension is about 0.25 mm; while in the secondary toughening process K R gradually increase, until the crack extension reaches 1 mm (for in_situ reinforcement) and 1.8 mm (for whisker reinforcement). The observations and the analyses indicate that, the two_step toughening behavior results essentially from the further debonding of the whisker-matrix interfaces (or the grain boundaries) in the crack bridging zone behind the crack tip , and the orientation angle of the whiskers (or the elongated grains) with respected to the normal direction of crack surface was the dominant cause for the further debonding.