Tadashi Hasegawa

Substructure formation and nonuniformity in strain during high temperature creep of copper single crystals

The change in substructure during high temperature creep of copper single crystals was examined to make clear the relation between the substructure and the creep rate. The structural observations by means of etch-pit technique were made in the same area of the specimen surface after successive straining by creep. Different types of substructures were formed in different localities at an early stage of transient creep. Small subgrains elongating in the direction of the deformation band were found in some regions (region A). Large subgrains containing cells within them were observed in other regions (region B). With the progress of creep, the substructures in both regions underwent gradual changes to become alike in their appearance with each other. The creep strains in regions A and B were examined at various creep stages. The ratio of creep strain to the average creep strain throughout the specimen,ε/εav, was a few times larger in region B than in region A at an early stage of transient creep. With the structural changes mentioned above, the difference between the ratios in the two regions came to disappear, both becoming almost unity at the later stage of creep. These results suggest the close relation between the substructure and the creep rate.

Effect of Cutting Fluids on Machinability of Aged Al-5.6mass%Cu-4.0mass%Si slloys

The effect of the cutting fluids on the machinability of Al-Cu-Si alloys which is candidate of the free cutting aluminum alloys without lead have been studied. The turning test was carried out using the cutting tool with the chip breaker. It was found that surface roughness after machining of the alloys became roughened, while the generation of the adhesion on the cutting tool was increased either in the dry or the wet cutting conditions. In the dry cutting, the chip breaking was better in the over aged alloys where the adhesion was easily generated. On the other hand, the chip breaking in the wet cutting was better in the under aged alloys where the adhesion was hard to generate. These results can be explained in terms of generation of the adhesion on the cutting tools ; in the dry cutting, the chip was greatly bent by the existence of the adhesion on the cutting edge of the cutting tool though, in the wet cutting, the chip breaker acted effectively by the adhesion was not easily generated.

NMR Study on the Electronic Structure of the Vortex State in HTSC

By using spatially-resolved NMR method, we observed nuclear spin-lattice relaxation rate (1/T1) of the vortex state to probe antiferromagnetic correlations at the vortex core. We found that the temperature dependence of 1/T1 shows a peak, which results from a local antiferromagnetic ordering of Cu spins in the vortex core.