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与墨西哥国家理工学院的Jose G.Cabanas参与一项联合研究计划，目的是提高我们对金属和合金疲劳的理解。西北大学研究小组在研究晶界微损伤、用于这些研究的双晶材料生长以及高温疲劳技术方面的经验将与墨西哥研究所在扫描和透射电子显微镜方面的经验结合起来。在西北大学，单晶铜或双晶铜将被生长，按预定的方向切割，并进行疲劳。使用扫描电子显微镜的选区沟道研究，以及使用透射电子显微镜的其他分析，将在国家理工学院进行，以研究疲劳材料中晶界迁移和附近发生空化的区域中的滑动、空化和位错结构之间的相互依赖关系。通过这些测量，可以揭示空穴和位错结构之间的关系，晶界的迁移，以及空穴生长的动力学。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的微观空洞和其他缺陷的关系，特别是当它们出现在晶界时，变得越来越重要。为了便于进行晶界效应的受控实验，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，扫描电子显微镜对晶体取向和完整性的沟道研究以及对晶界本身的透射电子显微镜研究可以给出晶界的运动以及这种运动与与疲劳有关的微观缺陷的关系。西北大学的首席研究员是这种双晶生长和取向方面的专家，而墨西哥的合作者在专业电子显微镜方面拥有互补的专业知识。这项研究将有助于回答高温疲劳引起的晶间损伤的某些基本问题，从而有助于开发适用于高温环境下的高应力材料。

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.