DEVELOPMENT AND APPLICATION OF SYNCHROTRON RADIATION DYNAMIC TOPOGRAPHY FOR OBSERVATION OF SECONDARY RECRYSTALLIZATION PROCESS

White X-ray topography by synchrotron radiation provides a powerful means for dynamic imaging and mapping of structural inhomogeneities in bulk materials. "Synchrotron radiation dynamic micro topography method" has been developed by a combination of a high performance furnace and a direct type X-ray TV camera to white synchrotron radiation for the best use of the highly bright and parallel beam of synchrotron radiation source at the Photon Factory in the National Laboratory for High Energy Physics. The method has been applied to dynamic observation of rapidly progressing phenomena at high-temperatures such as the migration of secondary recrystallization fronts in grain-oriented silicon steel. The migration of secondary recrystallization fronts is found not uniform in both time and location. Migrating fronts show a zigzag shape and move from protruding points preferentially. The migrating behavior shows the following three types: burst motion at a rate of 0.05 to 0.2 mm/s, gradual migration with 0.01 to 0.02 mm/s, and standstill state. The size of regions consumed by a front motion is constant and is as large as 0.2 to 1.0 mm in diameter. Dislocations are observed in the growing grains and subboundaries are formed by connection of migration fronts to surround retained areas.