Akihide Hosokawa

Multi-scale electron microscopy of overnitrided Sm-Fe-Mn-N powder

Multi-scale electron microscopy technique that combines transmission electron microscopy (TEM) and focused ion beam - scanning electron microscopy (FIB-SEM) was utilized to investigate the influences of the change in microstructure of Sm2(Fe0.95Mn0.05)17Nx by overnitridation on the magnetic properties. The recent high-contrast backscatter electron imaging technique in SEM machines enabled us to reveal the formation events of cell-like microstructure from a quite large field of view. In addition, detailed TEM observations revealed the crystallographic orientations of the cells as well as the local chemical fluctuation. The combination of these techniques allows us to understand the microstructural hierarchy in this material, verifying that the original orientations of the individual particles are inherited to the nanocrystalline cells formed by overnitridation.Multi-scale electron microscopy technique that combines transmission electron microscopy (TEM) and focused ion beam - scanning electron microscopy (FIB-SEM) was utilized to investigate the influences of the change in microstructure of Sm2(Fe0.95Mn0.05)17Nx by overnitridation on the magnetic properties. The recent high-contrast backscatter electron imaging technique in SEM machines enabled us to reveal the formation events of cell-like microstructure from a quite large field of view. In addition, detailed TEM observations revealed the crystallographic orientations of the cells as well as the local chemical fluctuation. The combination of these techniques allows us to understand the microstructural hierarchy in this material, verifying that the original orientations of the individual particles are inherited to the nanocrystalline cells formed by overnitridation.

Powder consolidation of Nd-Fe-B/α-Fe nanocomposite materials by cold deformation process

High-pressure torsion (HPT) was applied to Nd-Fe-B/α-Fe nanocomposite materials for the following two purposes. The first is to obtain anisotropic nanocomposite magnets by development of deformation texture, and the second is to consolidate bulk magnets directly from powder compacts without sintering process. Although no texturing occurred in this set of experiments, the consolidation was successful and increased the relative density up to 90% of a nanocomposite magnet having the coercivity Hc = 4.4 kOe and the remanence/saturation magnetization σr/σsat =100/165 emu/g. The shear strain gradient generated in a disc after HPT allowed us to discuss a relationship between shear strain and porosity, as well as the significance of shear in densification process.High-pressure torsion (HPT) was applied to Nd-Fe-B/α-Fe nanocomposite materials for the following two purposes. The first is to obtain anisotropic nanocomposite magnets by development of deformation texture, and the second is to consolidate bulk magnets directly from powder compacts without sintering process. Although no texturing occurred in this set of experiments, the consolidation was successful and increased the relative density up to 90% of a nanocomposite magnet having the coercivity Hc = 4.4 kOe and the remanence/saturation magnetization σr/σsat =100/165 emu/g. The shear strain gradient generated in a disc after HPT allowed us to discuss a relationship between shear strain and porosity, as well as the significance of shear in densification process.

Influence of the restored work-hardening rate on ductility studied by X-ray computed tomography

Abstract Void growth and coalescence in a model material containing an artificial three-dimensional void array (the estimated local void volume fraction was 1.1%) were investigated by X-ray computed tomography (=XCT). The initially tapered cylindrical voids became elongated along the principal straining direction by some amount of tensile plastic deformation, and then the work-hardening capacity in the intervoid matrix was restored by an intermediate annealing. The annealed model material was pulled in tension all the way up to fracture to see if the existing void coalescence models can predict the void coalescence strain.