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Analysis of Grain Boundary Microstructure and Grain Boundary Control

晶界微观结构分析及晶界控制

基本信息

批准号：
08242101
负责人：
WATANABE Tadao
金额：
$ 40.45万
依托单位：
Tohoku University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research on Priority Areas
财政年份：
1996
资助国家：
日本
起止时间：
1996 至 1998
项目状态：
已结题

项目摘要

Development of superplasticity is a key technology to overcome poor workability of intrinsically brittle materials such as refractory metals and ceramics. The goal of this project was to obtain a principle of grain boundary control and design to achieve superplasiticity. For this purpose, we quantitatively analyzed grain boundary microstructures such as the grain boundary character distribution (GBCD) in polycrystalline materials, and examined the relationship between superplastic behaviour and grain boundary microstructures. The chief results obtained are as follows :(1) Improvement of workability of brittle polycrystalline materials by controllinng grain boundary : Relationship between intergranular fracture behaviour and grain boundary microstructures was examined using systematically the grain size and the GBCD controlled molybdenum polycrystals. We have found that fracture strength depends on the grain size with the similar manner to the Hall-Petch relation. A particularly importa … More nt finding is that the observed Hall-Petch relation depends on the GBCD, in trun, the grain size dependence of fracture strength becomes more significant as the frequency of low Σ coincidence boundary decreases. In addition, we examined the evolution of grain boundary microstructures and cavitation at grain boundaries during superplastic deformation of Al-Li alloys. In the course of superplastic deformation, grain boundaries change their character towards increase in the frequency of random grain boundaries that slide more readily, and cavities preferentially nucleate at the grain boundary triple junctions where random grain boundaries interconnect. From these results, we provided insights on an optimized grain boundary microstructure not only to develop superplasticity but also to reduce cavitation damage.(2) Grain boundary structure and superplasticity in ceramic materials : Grain boundary structures in fine grained silicon carbides with addition of 7mol% AlィイD22ィエD2OィイD23ィエD2, 2mol% YィイD22ィエD2OィイD23ィエD2 and 1mol% CaO were observed by transmission electron microscopy. Then, development of superplasticity in SiC was examined in connection with the grain boundary structure. TEM observation revealed that the frequency of low angle and coincidence grain boundaries in SiC showing superplastic flow was ca. 25% and tended to decrease during deformation. We also investigated superplasticity in AlィイD22ィエD2OィイD23ィエD2/TiC composites that were sintered with different temperatures and with different amounts of TiC. A particular attention was paid to the role of TiC in superplastic deformation of AlィイD22ィエD2OィイD23ィエD2/TiC composite. A maximum superplastic elongation was obtained with the specimen containing 10 mol% TiC, and TiC particles were found to be responsible for retardation of grain growth in AlィイD22ィエD2OィイD23ィエD2. Less

发展超塑性是克服难熔金属和陶瓷等脆性材料加工性能差的关键技术。本项目的目标是获得晶界控制和设计的原则，以实现超塑性。为此，我们定量分析了晶界微观结构，如晶界特征分布（GBCD）在多晶材料，并检查超塑性行为和晶界微观结构之间的关系。（1）通过控制晶界改善脆性多晶材料的加工性能：利用晶粒尺寸和晶界缺陷控制钼多晶，系统地研究了沿晶断裂行为与晶界组织的关系。我们发现断裂强度与晶粒尺寸的关系与Hall-Petch关系相似。一个特别重要的 ...更多信息新的发现是，所观察到的Hall-Petch关系依赖于GBCD，而随着低重符合边界频率的降低，断裂强度的晶粒尺寸依赖性变得更加显著。此外，我们还研究了Al-Li合金超塑变形过程中晶界组织的演变和晶界空穴现象。在超塑性变形过程中，晶界改变其性质对随机晶界，更容易滑动的频率增加，和空洞优先形核的晶界三重连接处的随机晶界互连。从这些结果中，我们提供了一个优化的晶界微观结构的见解，不仅开发超塑性，但也减少空蚀损伤。(2)陶瓷材料中的晶界结构与超塑性：用透射电镜观察了添加7mol%Al_（22）Al_（23）Al_（22）Al_（23）Al_（22）Al_（23）Al_（然后，在SiC超塑性的发展进行了检查与晶界结构。透射电镜观察表明，SiC中出现小角度晶界和重合晶界的频率约为100%。25%，并在变形过程中趋于减少。我们还研究了在不同温度和不同TiC含量下烧结的Al_（22）Al_（23）/TiC复合材料的超塑性。重点研究了TiC在Al_（22）Al_（23当试样中TiC含量为10 mol%时，试样的超塑性延伸率最大，TiC颗粒对Al_（22）Al_（23）Al_（22）Al_（23）Al_（2少