Abstract
The microstructures of anisotropic Nd-Fe-Co-B-(Ga, or Zr) magnet powders produced by the hydrogenation-decomposition-desorption-recombination (HDDR) process and the resulting crystallographic c-axis orientation of Nd2(Fe,Co)14B crystals in the powder particles have been studied. It was found that the powder particles consist of fine Nd2(Fe,Co)14B crystals of the size of about 0.3 μm, and any boundary-layer phase between the Nd2(Fe,Co)14B crystalline grains is almost absent. The morphology of fine Nd2(Fe,Co)14B crystalline grains in anisotropic magnet powders is the same as that of isotropic magnet powders produced by the HDDR process. In anisotropic powders, it was found that there is a strong correlation among the a axes, b axes, and c axes of the fine Nd2(Fe,Co)14B crystal grains. The dispersion in solid angles made by the c-axis direction is less than ±18° in the case of Nd-Fe-Co-B-Ga magnet powder particle. The c-axis direction of fine grains in magnet powders produced by the HDDR process is associated with that of large Nd2(Fe,Co)14B grains in the original cast or the homogenized alloy. The microstructure of anisotropic magnet powders before the hydrogen desorption step in the HDDR process is very complicated. It consists of five distinct regions, and among these, two regions are made of NdH2 and Fe.
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