EFFECT OF GRAIN-BOUNDARY AND INTERPHASE STRUCTURES ON MECHANICAL PROPERTIES OF STRUCTURAL MATERIALS

单相材料的晶界和复合材料的界面是导致材料力学性能下降的主要原因。本研究对存在晶界脆性问题的钼、有望作为高温结构材料的Si_3N_4、SiC和TiC陶瓷以及IC工业中重要的微结合Au-Al，用高分辨透射电子显微镜观察了晶界结构和界面结构。它们的边界强度与边界结构有关。钼中的对称倾斜边界：断裂强度强烈地依赖于钼中的晶界特征。SIGMA 1低角度和近SIGMA 3重合边界相干性较好，而错向角在30 °左右的边界相干性较差。本文认为高共价键合的钼中的晶界结构与普通金属中的晶界结构没有太大的区别。Si_3N_4、SiC和TiC的晶界结构：在Si_3N_4和SiC中，在晶界处观察到类非晶层。用电子能量损失谱（EELS）分析了SiC中的这一层。结果表明，该层既不是烧结助剂层，也不是杂质层，而是一种弛豫结构。微结合Au-Al界面：在超薄切片机上没有观察到非晶相，而在离子铣削下，界面上形成的金属间化合物大部分为非晶相。使用用切片机制备的箔，澄清了污染对粘合的影响。

Grain boundaries of single phase materials and interphase boundaries of composite materials are often responsible for the degradation of mechanical properties. In the present investigation, for molybdenum which has problems of grain boundary brittleness, ceramics of Si_3N_4, SiC and TiC which are hopeful as high-temperature structural materials, and micro-bonded Au-Al which is important in the IC industry, the grain boundary structure and interphase boundary structure have been observed by means of high-resolution transmission electron microscopy. Their boundary strength is discussed in connection with the boundary structure.Symmetric tilt-boundary in Molybdenum: The fracture strength strongly depends on the grain boundary character in molybdenum. SIGMA 1 low angle and near SIGMA 3 coincidence boundaries have a good coherency, whereas the boundaries of misorientation angle around 30ﾟ are poor in coherency. However, the structure in those boundaries was found to be described by the grain-boundary dislocation model, It is considered that the grain boundary structure in molybdenum with a high covalency in bonding is not greatly different from that in normal metals.Grain boundary structure of Si_3N_4, SiC and TiC: An amorphous-like layer was observed at grain boundaries in Si_3N_4 and SiC. That layer in SiC was analyzed by EELS using a micro beam technique. It is clarified that the layer is neither sintering aids nor impurity layer but a relaxed structure. A grain boundary layer such as observed in Si_3N_4 and SiC was not observed in TiC where the boundary structure was metal like.Interphase boundary of micro-bonded Au-Al: In the foils prepared with a ultra-microtome no amorphous phase was observed, whereas in the foils prepared by ion milling a large part of the intermetallic compound formed on the interface was amorphous. Using the foils prepared with the microtome, the contamination effect on the bonding was clarified.