Shigeharu Hinotani

Effects of Fe3C and Mo2C precipitation on hydrogen diffusivity and hydrogen embrittlement in iron alloys

Abstract The effects of carbide precipitation on the diffusion of hydrogen atoms and hydrogen embrittlement in Fe-0.25wt.%C and Fe-3.9wt.%Mo-0.20wt.%C alloys have been investigated by means of the electrochemical permeation technique and tensile tests during cathodic charging of hydrogen. Although the effective hydrogen diffusivity in the FeMoC alloy decreases to the minimum value by tempering at temperatures at which secondary hardening is most prominent, the activation energy for it is independent of tempering temperature in both alloys, and the calculated binding energies between hydrogen atoms and traps are in the range 22–28 kJ mol −1 (almost the same as the binding energy for dislocations). The calculated trap density exhibits a tempering temperature dependence similar to that of the strength. The ductility and the fracture mode, however, are markedly affected by microstructural factors such as the high dislocation density, the almost continuous precipitation of fine Mo 2 C particles on the grain boundaries or the discontinuous precipitation of coarse Mo 2 C particles and the formation of precipitate-free zones in the vicinity of the grain boundaries, in addition to the average density of reversible or irreversible hydrogen-trapping sites.

Effect of nickel on hydride formation and hydrogen embrittlement in NiCrFe alloys

Abstract Hydride formation and hydrogen embrittlement in NiCrFe alloys were investigated with particular emphasis on the effect of nickel content. In all the alloys containing 30–60 wt.% Ni, γ hydride formed during cathodic hydrogen charging but, in the 30 wt.% Ni alloy, the formation of β hydride was also observed. During the decomposition of the hydride after the cessation of charging, surface cracks appeared along both the grain boundaries and the interfaces of {111} microtwins which were induced by the volume expansion due to the hydride formation. In the lower nickel alloys the formation of microtwins and the subsequent surface cracks along these interfaces were more pronounced. This probably arose from the decrease in stacking fault energy with decreasing nickel content. The ductility loss caused by cathodic hydrogen charging was much enhanced by increasing the nickel content, and the fracture mode changed from transgranular to intergranular. This change was quite similar to that observed in surface cracks and is thought to be related to the frequency of microtwin formation. Aging at 673 K suppressed hydrogen embrittlement, changed the fracture mode from intergranular to transgranular and reduced the amount of absorbed hydrogen. This can be explained in terms of the site competition mechanism due to the segregation of carbon atoms to the grain boundaries.

Application of fine-grained doubly oriented electrical steel to IPM synchronous motor

Application of fine-grained doubly oriented electrical steel sheets that have a strong {100}<001> texture to synchronous interior permanent magnet motors has been investigated. The alteration in stator core material from high grade nonoriented electrical steel sheets to the doubly oriented material with a simple change in stator design was found to lead to an increase in efficiency up to more than 2%. This efficiency increase is ascribed to a larger permeability and a lower iron loss in two perpendicular directions of the doubly oriented material. Finite-element analysis has revealed that the magnetic field distribution in stator cores made of the doubly oriented material is largely different from that in stator cores made of the nonoriented material.

Raman studies of orthorhombic YBa2−xSrxCu3O7−y

A Raman scattering study was performed in orthorhombic YBa2-xSrxCu3O7-y at room temperature. It is found that the Raman peak associated with Cu-O-Cu stretching mode along the c-axis (502 nm-1, x=0) increases continuously in frequency with increasing Sr content, while the bending mode of the Cu-O (341 cm-1, x=0) decreases in frequency. These results indicate that larger contraction of the Cu-O-Cu bond distance along the c-axis than that of the lattice constant along the c-axis of the orthorhombic unit cell can be attained by replacing Ba sites with Sr ions.

Raman studies on GaAs epitaxial films on Si

Abstract Raman spectroscopy has been applied to the study of the effects of thermal expansion and lattice mismatch between GaAs and Si on the stress in GaAs films. The amount of stress in GaAs films of various thicknesses has been estimated from the GaAs LO phonon frequency and the half-width. By correcting the measured GaAs LO phonon frequency by using the spatial correlation (SC) model, it is shown that compressive stress exists in GaAs films due to accommodation of the lattice mismatch when the film is very thin. It has been also found that the compressive stress decreases with increased film thickness. The misfit dislocations at theGaAs/Si interface have been investigated by HR-TEM. The density of misfit dislocations increases with increased film thickness. The compressive stress in GaAs films due to accommodation of the lattice mismatch is released mainly by an increase of the density of misfit dislocations at the heterointerface as the film thickness increases.

Fine-grained and cube-textured Si-steel sheet coil by oxide-separator-induced decarburization

Summary form only given. Although the energy efficiency of electrical apparatus, such as motors and transformers, could be significantly improved by the use of electrical steel sheets with cube texture {100} , applications of this kind of doubly-oriented steel to magnetic cores have been scarcely investigated. It has been found recently that a decarburizing annealing of a 3wt.%Si-1wt.%Mn-0.05wt.%C steel sheets with a SiO/sub 2/-containing separator gives rise to a remarkable evolution of the cube texture. In this process, neither inhibitors for grain growth, thinner thickness of steel sheets, nor cross-rolling is needed. In this paper, a hoop form of the cube-textured Si-steel sheets produced by this new method is introduced. The materials thus produced are evaluated in laboratory test, as well as by assembling a prototype motor.

Magnetic properties of fine-grained doubly oriented Si steel sheets

The magnetic properties of fine-grained doubly oriented Si steel sheets of 0.25–0.35 mm in thickness have been investigated. The doubly oriented Si steel sheets with grains of about 0.5 mm in diameter showed a large induction B8 of about 1.9 T as well as a 35% smaller core loss than the previously studied coarse-grained doubly oriented materials. This decrease in core loss associated with the grain size reduction is primarily due to a large decrease in eddy current loss. The core loss was further decreased by applying tensile stresses and by a reduction in sheet thickness. A tensile-stressed 0.25-mm-thick material showed a small core loss of 0.82 W/kg at 1.7 T and 50 Hz. The material also showed relatively small core losses under alternating fields below 500 Hz.The magnetic properties of fine-grained doubly oriented Si steel sheets of 0.25–0.35 mm in thickness have been investigated. The doubly oriented Si steel sheets with grains of about 0.5 mm in diameter showed a large induction B8 of about 1.9 T as well as a 35% smaller core loss than the previously studied coarse-grained doubly oriented materials. This decrease in core loss associated with the grain size reduction is primarily due to a large decrease in eddy current loss. The core loss was further decreased by applying tensile stresses and by a reduction in sheet thickness. A tensile-stressed 0.25-mm-thick material showed a small core loss of 0.82 W/kg at 1.7 T and 50 Hz. The material also showed relatively small core losses under alternating fields below 500 Hz.

Application of fine-grained doubly oriented electrical IPM synchronous motor

The magnetic core materials for motors have been mostly limited to non-oriented electrical steels of which crystallographic texture is almost random, although there is a possibility to greatly improve performance of motors by the use of steels with textures such as {100}<001>.The purpose of this research is to investigate how the performance of motors can be improved by the use of such a textured material by building actual motors using a doubly oriented electrical steel that has a strong {100}<001> texture. This key material in this investigation has been prepared by the process so-called oxide-separator-induced decarburization that has been found recently.