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 ρ f , 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 ρ f 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/cm 3 for the TT and LOT, respectively. At lower ρ f 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 param eters 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.

Effect of additions of zinc stearate on the properties of sintered Nd-Fe-B magnets

“…As the D av of the pow ders decreased to 2.6 μm, the oxygen content in the magnets prepared without the addition of zinc stearate increased to 0.43 wt %, but their coercive force remained almost unaltered. Note that, in the tradi tional technology [4], the application of dry powders with D av < 3.2 μm was accompanied by a sharp decrease in Н с , though the initial alloy contained a greater (by 1 wt %) amount of neodymium compared to the alloy employed in this work.…”

“…The texturing of the powders was per formed in solenoids of a pulsed field, which was applied in the direction parallel to the axis of the cylin drical cavity of the container. The degree of texture induced by the magnetic field in the powders was esti mated using the technique described in detail in [4]. In the descending segments of the hysteresis loops of the powders, which were measured in the closed circuit of the hysteresigraph in a field of 10 kOe, the value of the magnetization 4πM was determined, which was denoted as B 10 and was used as the measure of the degree of texture.…”

“…of Nd-Fe-B Powders A comparison of the degree of texture induced by a magnetic field in the powders that were produced with and without an addition of 0.15 wt % zinc stearate was performed by measuring B 10 [4]. Figures 1a-1d dis play the B 10 dependence on the maximum strength H m of the applied texturing field for dry powders with ρ f = 2.5, 2.7, 2.9, and 3.1 g/cm 3 , respectively.…”

“…The method of the estimation consisted of determination of the Zn concentration in the powder of the Nd-Fe-B alloy, calculation of the content of zinc stearate in powder samples on the basis of the formula C 36 H 70 O 4 Zn, and comparison of this content with the ratio between the components in the initial mixture. Due to the obvious smallness of the concentration of Zn in the objects under investigation, a Rigaku Nanohunter precision analyzer of the ele mental composition was used for its determination.…”

“…In our previous work [4], we studied the effect of the average particle size D av , filling powder density ρ f , and conditions of powder texture on the density ρ and magnetic hysteresis properties of sintered Nd⎯Fe-B magnets produced by the PLP using both traditional technology (TT) and low oxygen tech nology (LOT). In the first case, powders ground in a vibration mill in a toluene medium were dried in air; in the second case, grinding was performed in a jet mill using nitrogen as the working gas.…”