Tomotaka Miyazawa

Superspherical-shape approximation to describe the morphology of small crystalline particles having near-polyhedral shapes with round edges

Small crystalline particles are often formed comprising near-polyhedral shapes with round edges. When near-polyhedral shapes are analyzed and discussed, it is convenient if these shapes can be expressed by equations with simple parameters. Superspheres are solids expressing various shapes between those of polyhedra and spheres. The superspherical-shape approximation is used in this study to consider the morphology of cubic crystal structure particles. Various near-polyhedral shapes composed of {100}, {111} and {110} planes are described using a simple equation with three shape-related parameters. It is shown that the superspherical-shape approximation is a useful geometrical tool for evaluating the morphology of small crystalline particles.

In-situ X-ray diffraction during tensile deformation of ultrafine-grained copper using synchrotron radiation

Abstract At the synchrotron facility, Super Photon Ring – 8 GeV, in-situ X-ray diffraction during tensile deformation was conducted on ultrafine-grained Cu with a grain size of about 300 nm fabricated by equal-channel angular pressing. The diffraction profile was observed with the time resolution of about 1 s using multiple MYTHEN detectors, and the diffraction angle and the full-width at half-maximum of some Bragg peaks were determined using the pseudo-Voigt function. From the analysis of Bragg peaks, it was found out that there are microscopically three regions; elastic, plastic and transition regions. The 0.2% proof stress obtained from the stress–strain curve locates within the microscopic transition region. Microstrain was evaluated using the Williamson–Hall method and the dislocation density was also obtained from the microstrain. The dislocation density starts increasing before 0.2% proof stress, which is associated with dislocation bow-out and emission from grain boundaries. The Taylor relationship seems to be still satisfied after 0.2% proof stress.

Measurement of Distributions of Local Internal Stress Near Grain Boundary in SUS316 by EXDM Using White X-ray Micro Beam

The distributions of the local internal stress near the grain boundaries in 20 % cold-rolled SUS316 stainless steel were measured under the external tensile stress of 0 and 300 MPa using the Energy-dispersive X-ray Diffraction Microscopy (EXDM) technique at BL28B2 of SPring-8. The local internal stresses near the grain boundaries were successfully evaluated. The results indicated that the evidence that the internal stress concentration was occurred at the grain boundaries under the external tensile stress.