Preparation of sintered Nd-Fe-B magnets by pressless process

Abstract

Pressless process used for the preparation of sintered Nd-Fe-B magnets has been studied. The effect of the average particle size D av, filling density ρf, and powder-texturing conditions for obtaining density ρ and desired magnetic hysteretic properties of sintered magnets has been investigated for both traditional technology (TT) and low-oxygen technology (LOT). The ρf magnitude ensuring the optimum relation between the density ρ of sintered magnets and their degree of texture was shown to be 2.5–3.0 and 2.2 g/cm3 for the TT and LOT, respectively. At lower ρf magnitudes, no required density of sintered magnets is reached, whereas at higher filling densities, a low level of texture and low remanence are realized. Optimum parameters of pulsed field inducing the high degree of texture in powders have been determined. The following properties were achieved for magnets prepared by pressless LOT: B r ≥ 14.2 kG, H c ≥ 8 kOe, and (BH)max ≥ 47.9 MG Oe.