Site: Kyoto University
Graduate School of Energy Science
Kyoto 606-01, Japan
Fax: (81) 75-753 5464
Date Visited:25 July 1997
WTEC: C. Koch (report author), D.M. Cox, J. Mendel, H. Morishita, R.W. Siegel
This visit concentrated on the laboratory of one professor, Professor Paul Hideo Shingu at Kyoto University. He has a group of associates and graduate students (about 15) and is funded by the Ministry of Education, Science, Sports, and Culture (Monbusho).
Professor Paul Hideo Shingu was the WTEC panel's host. He is the Dean of the Graduate School of Energy Science at Kyoto University. He is a pioneer in the use of severe mechanical deformation to produce nanocrystalline (nc) microstructures. He was the first researcher to demonstrate the synthesis of nc materials by mechanical alloying (high energy ball milling) in the Ag-Fe immiscible system in a paper published in 1988. His group was the first to point out that nc materials can be made by MA. Much of his group's work in this area is summarized in a paper by P.H. Shiugu in Materials Transactions JIM 36:96 (1995). In order to be better able to define the mechanism(s) involved in creation of nc materials by severe plastic deformation, Prof. Shungu turned to the method of repeated press-rolling of component foils or powder mixtures. This "deterministic" mechanical alloying has allowed for both experimental studies of the developing microstructure ¾ by, for example, high resolution transmission electron microscopy (HRTEM) ¾ and the modeling of the microstructure by computer simulations. He and his coworker, Dr. K.N. Ishihara, have used chaos theory to model the microstructure obtained in shearing of dissimilar components, based on several simple approaches such as the baker's transformation, linear shear, and parabolic shear. The iteration of certain mapping generates chaos. It is noted that the application of precisely deterministic mapping can generate a chaotic mixing of initially macroscopically separated structures by a surprisingly small number of repeated applications of a mapping. This is analogous to the structures observed experimentally due to the mechanical deformation.
Among the systems Shingu's group has studied are immiscible systems such as Ag-Cu and Cu-Fe, which form metastable solid solutions; Ag-Fe, which forms an nc composite microstructure; and Co-Cu, which exhibits the giant magnetoresistance (GMR) effect.
The preparation of multilayers by repeated rolling requires careful control of the process. Component foils (or powder compacts) are first annealed in vacuum, pressed together in vacuum, annealed, then repeatedly rolled and annealed. The selected annealing temperature is critical to maintaining the planarity of the layers and to avoid their spheroidization, while relieving the deformation strains to allow further rolling.
HRTEM of the layered structures reveals nc grains within the layers, with rotation of the grain into an apparent epitaxial relationship with the other component.
The panel's other observations on this visit include the following:
A tour of the laboratory facilities revealed several critical processing devices such as a pseudo hot isostatic press (HIP), a good four-high rolling mill, and a vacuum hot press. Characterization facilities, such as a transmission electron microscope, are shared with others in the Department.
Professor Shingu's research differs in the smaller scale of his effort from that carried on by the large groups at national laboratories and IMR at Tohoku University. However, the innovative and creative studies done in his group have made significant contributions to the field of nanostructured materials.
See also Yasuna et al. 1997. J. Appl. Phys. 82(5):2435-2438.