液体急冷Nd-Fe-B合金の磁気特性に及ぼすC, Al, Si添加の効果

Abstract

We have studied the effect of C, Al and Si additions on magnetic properties of melt-spun Nd-Fe-B permanent magnet alloys. The compositions of the alloys were chosen to be Fe77.5Nd15(B1−xMx)7.5(M=C, Al, Si), 0.1≤x≤0.4. The crystallization temperature of the melt-spun amorphous alloys increased with increasing concentration of the forth elements M. The Curie temperature of the Nd2Fe14B phase increased with increasing concentration of Si, whereas it decreased with C and Al.The addition of the forth elements improved the magnetic properties. In the case of C addition, the intrinsic coercive field iHc was little changed compared with the ternary alloy, but the remanence Br showed high values in the composition range from x=0.15 to x=0.25, and the maximum energy product (BH)max was 1.6 to 1.8 times larger than that of the ternary alloy, which reached to maximal 93 kJ/m3(11.5 MGOe). In the case of Al, iHc was maximal 1.55 MA/m (19.5 kOe) in the range from x=0.15 to x=0.3, Br and (BH)max showed high values all over the range. Br and (BH)max showed high values also in the case of Si.The alloys, Fe77.5Nd15Al7.5 and Fe77.5Nd15Si7.5, showed poor hard magnetic properties, in which the Nd2Fe14M phase did not appear. Instead, Fe77.5Nd15C7.5 alloy showed a high iHc value(0.7 MA/m) in the specimen heat-treated at 1073 K, where the Nd2Fe14C phase was clearly observed.It is concluded from the variation of relative intensities of peaks of Mössbauer spectra that Al and Si atoms were preferentially substituted for one or two (k2 and probably j2) iron sites in the Nd2Fe14B phase, and C atoms occupied the B atom positions.