Papers by Author: Tomoyuki Kakeshita

Abstract: We have investigated the effect of particle size on martensitic transformation by using single crystalline specimens of an Fe-30at%Ni alloy by scanning electron microscope (SEM) observation, X-ray diffraction(XRD), magnetic susceptibility and magnetization measurements. As a result, we have found that an athermal martensitic transformation changes to an isothermal martensitic transformation with decreasing particle size. Considering the result of the TTT diagram, we have estimated the driving force for the martensitic transformation and the cluster size for nucleation of the isothermal martensitic transformation based on the model previously proposed.

Abstract: We have investigated effect of magnetic field at cryogenic temperature on the stability of austenitic phase in a sensitized SUS304 stainless steel. The sensitization of the steel was made by heat-treatment in vacuum at 973 K for 100h after the solution treatment at 1323 K for 0.5 h. Isothermal holding of the sensitized specimens was made under a static magnetic field of 5 T in the temperature range between 60 and 260 K for various holding times. As a result, the TTT diagram under the magnetic field corresponding to the formation of 0.5 vol. % of -martensite shows a double-C curve with two noses. We found that by the application of magnetic field, the nose temperature and the incubation time of upper part of the C-curve, that is due to the    transformation, become lower and shorter, respectively. On the other hand, the nose temperature of lower part of the C-curve, that is due to the      transformation, does not change under the magnetic field although the incubation time shortens by the application of magnetic field.