Synthesis of Hard Magnetic Nd-Fe-B Powders by a Thermochemical Process

Abstract

Fabrication of Nd-Fe-B magnetic powders by R-D process using ispray-dried precursors was tried. Due to stable formation of α-Fe as a primary phase as same as that in ingots, the herd magnetic Nd2Fe14 phase was not formed in the alloy powder with the composition of stoichiometric Nd2Fe14 unless excessive amount of Nd precursor or Ca was added in the process. However, this excessive addition, especially for Ca, led to abnormal grain growth of Nd2Fe14B. On the contrary, Nd2Fe14B was successfully obtained as a major phase from the alloy powder with the composition of Nd15Fe77B g without such excessive addition. The size of spherical shape Nd2Fe14B particles mostly consisted of one or more subgrains was less than 1 μm. The coercivity measured from this powder was relatively low (∼3 kOe) mostly due to residual CaO and soft magnetic phases.