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

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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.