In situ Observation of Crack Growth in Structural Ceramics and Microstructural Characterization

点击翻译按钮获取中文摘要

To clarify the micromechanisms of fracture and crack growth in engineering ceramics, microstructures in the process zone and zone wake of cracks were examined by transmission electron microscope (TEM) for the Si/SiC (TPCC) and PLS SiィイD23ィエD2NィイD24ィエD2 (TSN-03) ceramics which were subjected to fracture toughness measurement tests. The tests were carried out by a short bar method for the PLS SiィイD23ィエD2NィイD24ィエD2 ceramics and by a three-point bend test for the Si/SiC ones with chevron notched bean specimens. The three-point bend test was conducted at an elevated temperature (1673K) as well as at room temperature. As to the PLS SiィイD23ィエD2NィイD24ィエD2 (TSN-03) ceramics, it was found that microcracking appeared to be independent of dislocation structures. Some of grain boundary microcracks were connected with grain bridging phenomena. Main cracks were often observed to grow on the (0001) basal plane of an elongated β-SiィイD23ィエD2NィイD24ィエD2 grain. As to the Si/SiC ceramics, on the other hand, typical microstructures of the surfaces fractured at room temperature were characterized by stacking faults in the SiC grains and by dislocation structures in silicon phases. At elevated temperatures, crack temperatures, crack growth in transgranular modes would be related to the evolution of dense stacking faults. In addition, cyclic fatigue tests were also carried out on ZrOィイD22ィエD2 thin plate specimen to study fatigue crack growth behavior under cyclic stressing in plane bending from the microstructural points of view. The results were discussed in connection with martensitic transformation caused in the process zone wake of fatigue crack.