Analysis and control of microstructure of metal matrix composite under stress loading

本研究旨在分析颗粒增强金属基复合材料的颗粒、基体及其界面在静载荷下的微观行为，并明确其制备工艺对其性能的影响。首先在带变形台的扫描电镜下进行了原位拉伸试验。结果，测试成功地进行了检验，并且可以观察到均匀应力分布下由结构缺陷引起的微观结构退化。还发现，试样内部和表面也发生了相同的微观结构降解。采用粉末挤压法和熔体搅拌法制备了Al_2O_3和SiC颗粒分散铝合金复合材料。通过原位拉伸试验，观察了复合材料在拉伸加载过程中微观组织的变化。所有复合材料在最大加载前的加载点都有一些由于界面剥离和颗粒断裂而产生的微裂纹。由于基体的延展性，微裂纹不会在基体中扩展，但随着应变的增加，新的微裂纹数量增加。微裂纹的特征及其变化与复合材料的制备工艺有关。

The present research aims at analyzing microscopic behavior of particles, matrix and their interfaces of particle reinforced metal matrix composites during static loading and making clear the effects of their fabricating processes on the behavior. The in situ tensile test in the scanning electron microscope equipped with a defromation stage was investigated at the first of all. As the result the test was successfully examined and it was possible to observe only microstructural degradation owing to structural defects under homogeneous stress distribution. It was also found that the same microstructural degradation was occurred inside the specimen as wel as that observed on its surface.Some Al_2O_3 and SiC particle dispersed aluminum alloy composites were produced with the powder extruding and melt stirring methods. The change in microstructure of the composites was observed continuously during tensile loading by the in situ tensile test. Some microcracks owing to the interface debonding and the particle fracture are initiated at early loading point before maximum loading in all composites. The microcracks do not propagate in the matrix because of its ductility, but the number of new microcracks are increased with inceasing strain. The character of the microcracks and their change are depend on the fabricating process of the composites.