Ryoji Nakayama

Anisotropic Nd/sub 2/Fe/sub 14/B based magnet powders with high remanences produced by modified HDDR process

The hydrogenation-decomposition-desorption-recombination (HDDR) process is a unique method to produce anisotropic Nd/sub 2/Fe/sub 14/B-based magnet powder for bonded magnet application. In this study, we studied the effect of appending the intermediate Ar (IA) treatment, i.e., hydrogenated materials are annealed under an Ar atmosphere before the evacuation treatment in the HDDR process, on the magnetic properties of magnet powder. It was found that the IA treatment is very effective to enhance magnetic anisotropy of the powder. The optimum magnetic properties of the anisotropic bonded magnet made from the IA treatment processed Nd/sub 12.6/Fe/sub bal./Co/sub 17.4/B/sub 6.5/Zr/sub 0.1/Ga/sub 0.3/ powder are as follows: B/sub r/=1.06 T, H/sub cJ/=992 kA/m, and (BH)/sub max/=193 kJ/m/sup 3/. It was observed that the IA treatment induces rapid growth of a /spl alpha/-(Fe,Co) grains in the decomposed mixture of the alloy. This microstructural change of the alloy is considered to be strongly related to the preferred crystallographic orientation of the final magnet powder.

Preparation of fully dense Nd–Fe–B magnets using semi-processed HDDR powders

Abstract Anisotropic fully dense Nd–Fe–B magnets can be produced by compacting the hydrogenation-decomposition-desorption–recombination (HDDR)-processed powder under an orienting magnetic field, and then hot pressing the green compacts. In this study, magnetic properties of the hot pressed magnets made from Nd 12.7 Dy 0.3 Fe 64.3 Co 16.0 B 6.2 Zr 0.1 Ga 0.4 powders in the different stages of the HDDR process were investigated with regard to the degree of powder particle orientation. It was found that the powder in which small amounts of the decomposed NdH 2 and α -(Fe, Co) phases remain (semi-processed powder), can be more highly oriented in applied magnetic fields less than 1190xa0kA/m as compared to the fully HDDR-processed powder. The magnet with B r =1.13xa0T, H cJ =1280xa0kA/m, and ( BH ) max =230xa0kJ/m 3 can be obtained by dehydrogenating the green compact of the semi-processed powder completely before hot pressing.

Magnetic properties of anisotropic Nd–Fe–B HDDR powders prepared from strip cast alloys

Abstract Anisotropic hydrogenation–decomposition–desorption–recombination (HDDR)-treated powders were prepared from strip cast (SC) Nd10.1Pr2.9Fe74.6Co5.8B6.2Zr0.1Ga0.3 alloy flakes. The alloy flakes were annealed at various temperatures before the HDDR treatment. Br and (BH)max of the powder are increased as the annealing temperature increases from 1000 to 1160xa0°C, which can be ascribed to growth of the original Nd2Fe14B grains. The powder obtained from the optimally annealed alloy flakes, exhibits Br of 1.46xa0T, HcJ of 1210xa0kA/m, and (BH)max of 388xa0kJ/m3, which are superior to those of the powder prepared using the conventional book-mold cast (BMC) ingots. This would be related to the complete elimination of α-Fe phase in the strip cast flakes.

Influences of original alloy microstructure on magnetic properties of isotropic HDDR-treated Nd–Fe–B powder

Abstract Influences of original alloy microstructure on magnetic properties of the isotropic hydrogenation-decomposition-desorption-recombination-treated Nd 12.6 Fe 79.0 Co 2.4 B 6.0 powder were studied using two types of starting materials, i.e., the strip cast (SC) alloy and the conventional book-mold cast (BMC) alloy. It was found that the powder prepared from the SC alloy exhibits better I – H loop squareness and higher remanence than the powder from the BMC alloy. The powder obtained from the SC alloy consists of the recombined Nd 2 Fe 14 B grains with more uniform size, which is thought to be closely related to its good loop squareness. The effect of using the SC alloy could be attributed to the complete elimination of α-Fe phase.

Microstructure control in HDDR process for higher anisotropic Nd-Fe-B magnet powders

Homogenized Nd-Fe-Co-B-Zr(-Ga) alloys are treated by hydrogenation (HD-process) and dehydrogenation (DR-process) with various treatment conditions, followed by quenching in argon gas flow. After the HDDR process, the specimens are crashed into powders. The magnetic properties of the powder and bonded magnets are measured with a vibrating sample magnetometer and a B-H tracer. The microstructural changes are also analyzed by electron microscopy (FE-SEM and TEM) and discussed with special reference to the behavior of boron.