"Grain Boundary Sliding, Fracture and Dislocation Motion in Ceramics"
By Yuichi Ikuhara, The University of Tokyo /Japan Fine Ceramics Center, Japan
Abstract
Ceramics have been widely used for structural applications because of their superior mechanical properties at high temperatures. It has been known that the behavior of GB sliding is strongly dependent on the GB characters such as misorientation angle between two adjacent crystals and GB plane, however, such effect has not been clarified yet. In addition, this effect in much influenced by dopant segregation at GBs. In this study, in order to clarify the atomistic mechanisms of GB sliding and its dopant effect, bicrystal studies have been performed to find the relationship between the atomic structures, chemistry and GB sliding behavior of Al2O3 ceramics. Several kinds of bicrystals including GBs with specific geometrical configuration were fabricated, and some of them were doped by rare-earth elements to enhance the GB segregation.
It has been reported that several oxides can be plastically deformed even at R.T. by dislocation slip like metals. So far, many experimental investigations have been tried for understanding the dislocation-grain boundary interaction, but these experiments were mostly carried out statically, and the fundamental processes are still not well understood yet. In this study, the nanoindentation experiments were conducted for SrTiO3 crystals their bicrystals inside TEM. Several kinds of TEM specimens for in situ nanoindentation experiments were prepared, that are single crystals and bicrystals including various types of GBs. The SrTiO3 single crystals were indented with the sharp diamond tip and successfully observed the dislocation dynamics. In the case of the GBs, the interaction between the introduced lattice dislocations and the GBs were directly observed. The dislocation-GB interaction and its dependence on the GB characters will be discussed in detail.
Speaker Biography
Professor Yuichi Ikuhara is Professor and Director of Nanotechnology Center, Institute of Engineering Innovation at University of Tokyo since 2003. He received Dr.Eng. from Department of Materials Sciences, Kyushu University. He then joined Japan Fine Ceramics Center (JFCC) in 1988, and was the Microstructure Characterization Division Manager at JFCC from 1993. In 1996, he joined University of Tokyo as an associate professor of Materials Sciences. He was a visiting assistant professor at Case Western Reserve University from 1991 to 1993. His current research interest is in interface and grain boundary and interface phenomena, advanced transmission electron microscopy (STEM, HREM, EDS, EELS), high-temperature ceramics, dislocation technology, phase transformation, theoretical calculations and so on. Dr.Ikuhara is author and coauthor of about 720 scientific original papers in this field, and has more than 350 invited talks at international and domestic conferences. He received “Medal with Purple Ribbon”from the Emperor of Japan (2016), “Humboldt Research Award”from Alexander von Humboldt Foundation (2010), “Honda Frontier Prize” from Honda Foundation (2010), “Sosman Lecture Award” (2015) and “Ross Coffin Purdy Award” (2008) from the American Ceramics Society and so on. He is a fellow of the American Ceramics Society (2011), member of World Ceramic Academy (2014), and an associate member of the Science Council of Japan. He holds a group leader position at JFCC and WPI (World Premier International Research Center Initiative) professor at Tohoku University concurrently.
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Abstract
Ceramics have been widely used for structural applications because of their superior mechanical properties at high temperatures. It has been known that the behavior of GB sliding is strongly dependent on the GB characters such as misorientation angle between two adjacent crystals and GB plane, however, such effect has not been clarified yet. In addition, this effect in much influenced by dopant segregation at GBs. In this study, in order to clarify the atomistic mechanisms of GB sliding and its dopant effect, bicrystal studies have been performed to find the relationship between the atomic structures, chemistry and GB sliding behavior of Al2O3 ceramics. Several kinds of bicrystals including GBs with specific geometrical configuration were fabricated, and some of them were doped by rare-earth elements to enhance the GB segregation.
It has been reported that several oxides can be plastically deformed even at R.T. by dislocation slip like metals. So far, many experimental investigations have been tried for understanding the dislocation-grain boundary interaction, but these experiments were mostly carried out statically, and the fundamental processes are still not well understood yet. In this study, the nanoindentation experiments were conducted for SrTiO3 crystals their bicrystals inside TEM. Several kinds of TEM specimens for in situ nanoindentation experiments were prepared, that are single crystals and bicrystals including various types of GBs. The SrTiO3 single crystals were indented with the sharp diamond tip and successfully observed the dislocation dynamics. In the case of the GBs, the interaction between the introduced lattice dislocations and the GBs were directly observed. The dislocation-GB interaction and its dependence on the GB characters will be discussed in detail.
Speaker Biography
Professor Yuichi Ikuhara is Professor and Director of Nanotechnology Center, Institute of Engineering Innovation at University of Tokyo since 2003. He received Dr.Eng. from Department of Materials Sciences, Kyushu University. He then joined Japan Fine Ceramics Center (JFCC) in 1988, and was the Microstructure Characterization Division Manager at JFCC from 1993. In 1996, he joined University of Tokyo as an associate professor of Materials Sciences. He was a visiting assistant professor at Case Western Reserve University from 1991 to 1993. His current research interest is in interface and grain boundary and interface phenomena, advanced transmission electron microscopy (STEM, HREM, EDS, EELS), high-temperature ceramics, dislocation technology, phase transformation, theoretical calculations and so on. Dr.Ikuhara is author and coauthor of about 720 scientific original papers in this field, and has more than 350 invited talks at international and domestic conferences. He received “Medal with Purple Ribbon”from the Emperor of Japan (2016), “Humboldt Research Award”from Alexander von Humboldt Foundation (2010), “Honda Frontier Prize” from Honda Foundation (2010), “Sosman Lecture Award” (2015) and “Ross Coffin Purdy Award” (2008) from the American Ceramics Society and so on. He is a fellow of the American Ceramics Society (2011), member of World Ceramic Academy (2014), and an associate member of the Science Council of Japan. He holds a group leader position at JFCC and WPI (World Premier International Research Center Initiative) professor at Tohoku University concurrently.
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