DEPENDENCE OF MAGNETISM OF Nd-Fe-B SINTERMAGNETS ON ORIENTATION MAGNETIC FIELD

The effect of the orientation magnetic field on the permanent magnetism of Nd-Fe-B sintermagnets is investigated. The results show that the variation law of magnetism with orientation field obviously changes at the critical orientation field and the intensity of the orientation field should he determined by the dimension ratio of the magnet for effectively utilizing its magnetic energy product.

Rare earth permanent magnets prepared by hot deformation process

Hot deformation is one of the primary methods for fabricating anisotropic rare earth permanent magnets. Firstly,rapidly quenched powder flakes with a nanocrystal structure are condensed into fully dense isotropic precursors using the hot-pressing process. The prepared isotropic precursors are then hot-deformed to produce high-anisotropy uniaxial bulk rare earth permanent magnets and a highly textured structure is produced via this process. The resulting magnets possess many advantages such as near-net-shape, outstanding corrosion resistance, and ultrafine-grain structure. The influence of the preparation parameters utilized in the hot-pressing and deformation processes on the magnetic properties and microstructure of the permanent magnets are systemically summarized in this report. As a near-net-shape technique, the hot deformation process has notable advantages with regard to the production of irregular shapes, especially for radially oriented ringshaped magnets with high length-diameter ratios or thin walls. The difficulties associated with the fabrication of crack-free,homogeneous, and non-decentered ring-shaped magnets are substantially resolved through an emphasis on mold design,adjustment of deformation parameters, and application of theoretical simulation. Considering the characteristics of hotdeformed magnets which include grain shape and size, anisotropic distribution of intergranular phases, etc., investigation and improvement of the mechanical and electric properties, in addition to thermal stability, with the objective of improving the application of hot-deformed magnets or ring-shaped magnets, is of practical significance.

Relation of the Coercivity with the Grain Alignment Degree in Nd－Fe－B Sintermagnets

The experimental results show that the coercivity of Nd-Fe-B sintermagnet decreases with increasing of the grain alignment degree of the magnets (i.e. decreasing of the orientation distribution coefficient σ).The coercivities of the magnets with different orientation degree are calculated based on the pinning,nucleation and starting field theory,respectively.The comparison of the calculated values with the experimental results shows that the theoretical results are deviating from the experiments seriously for both pinning mechanism and nucleation mechanism. In contrast with that,the calculated values based on the starting field theory are in good agreement with the experimental results.

Effect of Cutting Techniques on the Structure and Magnetic Properties of a High-grade Non-oriented Electrical Steel

The high grade non-oriented electrical steel sheets containing 3.0%Si were manufacturing processed using different cutting techniques, then they were stress relief annealed（SRA）, the profiles and textures of the cutting edges were compared before and after annealing, and the magnetic properties of these specimens were tested and compared. The experimental results show that the iron loss of the specimen by water jet cutting is the lowest, but the magnetic induction under the low magnetic field is the highest, the iron loss of the specimen by laser cutting is the highest, but the magnetic induction under the low magnetic field is the lowest. It is necessary to adopt suitable production conditions and minimize the deterioration involved, and the magnetic property can be recovered by SRA effectively.

Method to Identify the Material of a Single Grain Based on Its Magnetization and Anisotropy Measured in a Chamber Type μG Drop Shaft

Free translation caused by attractive field-gradient force was observed for Ni and ferrite(CuFe_2O_4) grains that were released in a diffuse area.In order to exclude the effect of terrestrial gravity,translation was observed in micro-gravity(μG) condition produced by a compact drop-shaft installed in a ordinary laboratory room.Magnetization Ms per unit mass of the grain is obtained by analyzing the above-mentioned translations in terms of a energy conservation rule;here conservation of the sum of field-induced potential mMsH and kinetic energy 1/2/mv^2 is considered for a particle with mass m.The present method of obtaining Ms is free of measuring the mass of sample;this is because the field-gradient force is a volume force that is proportional to m.The method is also free of an interfering signal emitted from the sample holder.Accordingly,Ms is detectable irrespective of sample size,provided that the field-induced translation is observable.The above-mentioned procedure to estimate Ms from filed-induced translation is a step to obtain a reliable magnetic data from a single nano-sized grain.The efficiency of material identification was recently confirmed on various solid grains,which was based on diamagnetic magnetization data obtained from its translations caused by field-gradient repulsive force.A diamagnetic material generally possesses an intrinsic value of magnetic susceptibility and its anisotropy.The present results on nickel grains indicate that the principle of material identification based on its magnetization data is applicable for the three major category of magnetic materials,namely ferro-(or ferri-) magnetic, paramagnetic and diamagnetic material.

Investigating Magnetic Field Orientation as an Operational Parameter in Thermoelectric MHD Solidification

A fully coupled 3-dimensional numerical model is used to analyse the effect of magnetic field orientation on dendritic growth.For materials that exhibit a significant thermoelectric power,the results show significant differences in the dendritic morphology for different orientations of the field.These variations can be attributed to fluid flow generated through Thermoelectric Magnetohydrodynamics.A simplified,steady-state,low-field solution during the early stages of growth is used to describe how the fluid flow alters with the orientation of the field and how these flow features can lead to the final morphologies for well developed dendrites.