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262 Appendix D. Site Reports—Japan
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:
• the rolling of mixed powder compacts has produced results similar to
those with foils
• a number of mechanical and magnetic measurements have been made on
these samples
• it is believed this method of repeated rolling could be scaled up to
commercial quantities, since rolling technology is well developed in the
steel industry, as one example
• Shingu’s group consists of several professionals, one technician, and
15-20 graduate students
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.
REFERENCE
See also Yasuna et al. 1997. J. Appl. Phys. 82(5):2435-2438.