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相界往往是导致力学性能退化的原因。本文对存在晶界脆性问题的钼，有望作为高温结构材料的氮化硅、碳化硅和碳化钛陶瓷，以及在集成电路工业中具有重要意义的微结合金铝材料，用高分辨电子显微镜观察了晶界结构和相界结构。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小角和接近Sigma 3的重合边界具有良好的相干性，而30ﾟ左右的错位角的边界相干性较差。然而，晶界结构符合晶界位错模型，认为共价性较高的钼的晶界结构与普通金属没有太大差别。Si3N4、SiC和TiC的晶界结构：在Si3N4和SiC的晶界观察到类非晶层。用EELS微束技术对碳化硅中的这一层进行了分析。结果表明，该层既不是助烧剂，也不是杂质层，而是一种松弛结构。在TiC中没有观察到Si_3N_4和碳化硅中观察到的晶界层，其边界结构为金属状。微结合Au-Al：在用超微切割机制备的薄片中没有观察到非晶相，而在离子球磨制备的薄片中，界面上形成的金属间化合物大部分是非晶态的。利用显微切片机制备的薄片，阐明了污染对粘接效果的影响。

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.