Naoyuki Sano

Crystallization process of a rapidly quenched Fe-B-Nd nanocomposite magnet

Abstract Superior magnetic properties of Nd–Fe–B nanocomposite magnets rely on their nanoscaled structure composed of hard-magnetic Nd 2 Fe 14 B and soft-magnetic Fe 3 B phases, which results from a glassy state upon subsequent annealing. It has been known from X-ray diffraction (XRD) analysis that for this system, an addition of Cr is critical to control the crystallization route to produce the desired mixture of Nd 2 Fe 14 B and Fe 3 B phases. We have investigated the partitioning of Cr in a Nd 5 Fe 74.5 B 18 Cr 2.5 alloy throughout its crystallization process using atom probe field ion microscopy (APFIM). Cr is found to be enriched in Fe 3 B, up to 4.7 at.%, and the Cr concentration in Nd 2 Fe 14 B is determined to be 0.70 at.%. Together with the results of XRD, we have discussed the effect of Cr, based on the idea that Cr alters the phase decomposition route by stabilizing the Fe 3 B phase.

Cube-textured Si-steel sheets by oxide-separator-induced decarburization and growth mechanism of cube grains

Oxide-separator-induced decarburization causes a pronounced cube-texture development in Si-steel sheets. Cube grains nucleate prior to the decarburization, and they then selectively grow when a diffusion-induced transformation occurs. The 0.35 mm thick cube-textured strips show 2D magnetic properties with an almost ideal four-fold symmetry as well as surprisingly low core losses in the easy magnetizing directions.

Effect of Cr-doping on crystallization sequence and magnetic properties of Fe3B/Nd2Fe14B nanocomposite permanent magnets

Abstract Crystallization sequence starting from Nd x Fe 82 − x B 18 and Nd x Fe 79 − x Cr 3 B 18 (x = 3.5 – 5.5 at%) amorphous alloys has been investigated using X-ray diffractometer. In the alloys with Nd concentration around 5 at%, the intermediate compound Nd 2 Fe 23 B 3 first crystallizes along with Fe 3 B from the amorphous state. Then, the Nd 2 Fe 23 B 3 phase decomposes to form a mixture of Nd 2 Fe 14 B, Fe 3 B and αFe for the Cr-bearing systems, whereas it breaks up into another mixture of αFe and NdFe 4 B 4 for the Cr-free systems. Atom probe field ion microscopy analysis has revealed that Cr is preferentially partitioned into the Fe 3 B phase during the crystallization process, which may stabilize the Fe 3 B-containing mixture exhibited in the Cr-doped systems. We can conclude that a large fraction of Nd 2 Fe 14 B produced from the distinct decomposition scheme of the intermediate Nd 2 Fe 23 B 3 phase exhibited in the Cr-doped systems brings about the high coercivity materials.

ORIENTATIONAL MEMORY SITE IN HYDROGENATION DISPROPORTIONATION DESORPTION RECOMBINATION PROCESS OF ANISOTROPIC ND2FE14B-BASED MAGNETS

To clarify the orientational memory site in the hydrogen disproportionation desorption recombination process of Nd2Fe14B-based anisotropic magnets, high resolution transmission electron microscopy (HRTEM) characterization of hydrogen disproportionated structure of Nd13.0Fe67.9Co11.0Ga1.0Zr0.1B7.0 has been performed. In particular, crystallographic orientations of disproportionated products relative to that of parent or original Nd2Fe14B have been carefully analyzed using partially disproportionated samples. No apparent orientational coherency exists between the disproportionated products of α-Fe, Fe2B, and NdH2 and the parent Nd2Fe14B. However, nanoscale Nd2Fe14B particles of 10 to 100 nm in diameter have been detected by HRTEM to be densely present within the disproportionated mixture. Lattice fringe observation has also revealed that the crystallographic axes of the Nd2Fe14B particles are nearly parallel to those of the original Nd2Fe14B. It is thus suggested that these Nd2Fe14B particles be the orienta...

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.

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.

Ga site occupancy in HDDR-treated Nd2Fe14B-based alloy by XAFS

Abstract The changes of local structure for Ga in Nd 13.0 Fe 68.2 Co 10.8 Ga 1.0 Zr 0.1 B 6.9 during hydrogenation, disproportionation, desorption and recombination (HDDR) process are studied by fluorescence XAFS in order to understand the evolution of magnetic anisotropy by HDDR process. Comparing the observed Ga XAFS data with the calculated ones, using ab initio calculation (FEFF), Ga is proved to occupy preferentially an Fe(c) site in the Nd 2 Fe 14 B structure before disproportionation and dissolves in α-Fe after the disproportionation. In the recombined state Ga redistributes into two phases, i.e. Nd 2 Fe 14 B and a Nd-rich phase. The behavior of Ga during the HDDR process differs from Zr which occupies Fe(j 2 ) sites before disproportionation and after the disproportionation.

Effect of Prior Heat Treatment on Hardness Profile after Nitrocarburization in Medium Carbon Steel

Gaseous ferritic nitrocarburization is one of the major surface hardening methods to improve the fatigue strength of machinery parts made of medium carbon steels. The fatigue strength of nitrocarburized steel parts depends on the hardness profile below the surface; however, the mechanism of its evolution during nitrocarburization has not been fully understood. Recently, as-forged steels, in which thermal refining process like normalizing is omitted from the viewpoints of environmental considerations, energy savings and manufacturing cost reductions, have been widely used in the machinery parts industry. Therefore, it is important to understand the mechanism of hardness increase below the surface of the nitrocarburized steels with respect to the effect of prior refining heat treatment. In the present study, the hardness increase at the subsurface region of nitrocarburized steels containing 0.4mass%C was characterized, and the influence of prior normalizing treatment was investigated. Microstructure of both the as-forged and the normalized specimens was the ferrite/perlite mixture, while the ferrite volume fraction in the as-forged steel was smaller than the latter. These as-forged and normalized steels were gaseous nitrocarburized at 853K for 2 hours under the atmosphere of RX gas and NH3 gas mixture, and then they were oil-quenched to 373K. Overall hardness below the surface after nitrocarburization was higher for the specimen without prior normalizing treatment, although both specimens had the similar nitrogen concentration profiles and precipitation behaviors of the nitrides. However, it was found that the individual ferrite grains in the as-forged steel were more hardened than those in the normalized steel. These indicate that the most likely cause of the hardness increase near the surface after nitrocarburization is the solid solution hardening by dissolved nitrogen and that the ferrite grains of the as-forged steel were likely to soak up more nitrogen and were hardened to the higher degree since the similar amount of nitrogen were incorporated mainly within ferrite grains. Thus, the prior heat treatment strongly affects the amount of hardening through the ferrite fraction.

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.

Simulation of FIM images of precipitation-hardening alloys

Abstract The simulation of FIM images for precipitation-hardening alloys based on the shell model is presented, by which quantification and visualization of precipitates are possible. Both spherical and platelet precipitates are drawn with various parameters. This simulation is useful for quantitative analysis of FIM images being observed, and of FIM photographs. The modified stereographic projection is shown to have some advantage of reducing the apparent size difference of precipitate particles and diminishing distortion of images for off-axis projection.