Nd-Fe-B anisotropic bonded magnets

To understand the role of the Ga addition which enhances coercivity in Nd14Fe79.25B6Ga0.75 die upset magnets, metallurgical investigations using Auger electron spectroscopy (AES) and energy-dispersive x-ray spectroscopy-transmission electron microscopy (EDX-TEM) were done. Ga has a tendency to be condensed in the Nd rich phase (higher than 2 wt%) and Ga content in the matrix is around 0.2 wt%. The Ga solution in these phases seems to strengthen the pinning force defined at the interface of the matrix and the Nd rich phase. To improve thermal stability further, the Co substitution for Fe in Nd14Fe79.25-μCoμB6Ga0.75 (μ = 0 to 20) magnets was investigated. The Co substitution up to μ = 20 does not decrease coercivity, while for sintered magnets the Co substitution decreases coercivity very markedly. The irreversible losses for μ = 0 and 7.5 after exposure at 1800C are over 10% and under 5%, respectively. Using pulverized Nd14Fe71.75Co7.5B6Ga0.75 die-upset magnets, anisotropic bonded magnets (compression molded) with 15 MGOe of (BH)max and 19 kOe of iHc were obtained. The irreversible loss is under 5% after exposure up to 1400C. The results of these studies are detailed in this paper