U.S.-Mexico Cooperative Research on Grain Boundary Phenomena in Oriented Bicrystals Subjected to High Tempature Fatigue

该奖项支持西北大学的Julia R. Weertman与墨西哥国立理工学院的Jose G. Cabanas的联合研究项目，旨在提高我们对金属和合金疲劳的理解。西北大学研究小组在晶界微损伤研究、用于这些研究的双晶材料生长和高温疲劳技术方面的经验将与墨西哥机构在扫描和透射电子显微镜方面的经验相结合。在西北大学，单晶或双晶铜将被生长，以预定的方向切割，并进行疲劳处理。在国立理工学院，将使用扫描电子显微镜进行选择区域通道研究，并使用透射电子显微镜进行其他分析，以研究疲劳材料的晶界迁移和滑动，空化和空化发生附近区域的位错结构的相互依赖性。从这些测量结果中，可以看出空腔与位错结构之间的关系、晶界的迁移以及空腔生长的动力学。随着对现代材料的要求越来越高，金属和合金中的疲劳，以及疲劳失效与材料中微观空洞和其他缺陷的关系，特别是当它们发生在晶界时，变得越来越重要。为了便于对晶界效应进行控制实验，可以使用从适当取向的双晶中分离出来的“模型晶界”。在受控条件下疲劳后，通过扫描电子显微镜对晶界取向和完善的通道研究以及透射电子显微镜对晶界本身的研究，可以表明晶界的运动及其与疲劳相关的微缺陷的关系。西北大学的首席研究员是这种双晶体生长和定向方面的专家，而墨西哥合作者在专业电子显微镜方面具有互补的专业知识。这项研究将有助于回答有关高温疲劳产生的晶间损伤的某些基本问题，从而有助于开发适合在高温环境下高应力使用的材料。

This award supports the participation of Julia R. Weertman of Northwestern University in a program of joint research with Jose G. Cabanas of the Instituto Polytecnico Nacional of Mexico with the goal of improving our understanding of fatigue in metals and alloys. The experience of the Northwestern University research group in the study of micro-damage at grain boundaries, in the growth of bicrystalline materials for these studies, and in techniques for high-temperature fatiguing, will be combined with the experience at the Mexican institution in scanning and transmission electron microscopy. Single or bicrystalline copper will be grown, cut in predetermined orientations, and fatigued, at Northwestern. Selected-area channeling studies using a scanning electron microscope, and other analyses using transmission electron microscopy, will be performed at the Instituto Polytecnico Nacional to study the interdependence in fatigued material of grain boundary migration and sliding, cavitation, and dislocation structure in the region near where cavitation occurs. From these measurements light should be thrown on the relationship between cavities and dislocation structure, on the migration of grain boundaries, and the dynamics of void growth. Fatigue in metals and alloys, and the relationship of fatigue failure to microscopic voids and other defects in materials particularly as they occur at grain boundaries, are of increasing importance as more is asked of modern materials. In order to facilitate the performance of controlled experiments on grain-boundary effects, "model grain boundaries" which are isolated from properly oriented bicrystals, may be used. After fatiguing under controlled conditions, scanning electron microscopy channeling studies of crystalline orientation and perfection and transmission electron microscope investigation of the boundaries themselves can give an indication of the motion of grain boundaries and the relationship of this motion to micro-defects related to the fatigue. The Northwestern University principal investigator is an expert in the growth and orientation of such bicrystals while the Mexican collaborator has complementary expertise in specialized electron microscopy. This research should help answer certain fundamental questions regarding intergranular damage produced by high-temperature fatigue, and thereby contribute to the development of materials suitable for high-stress use in high-temperature environments.