Nd9Fe85.5-xCoxB5.5 (x=0,1,3,5)合金快淬薄带及其热变形磁体的微观组织与矫顽力

Microstructures and Coercivity of the Melt-Spun Ribbons and Die-Upset Magnets of Nd9Fe85.5-xCoxB5.5 (x=0, 1, 3, 5) Alloys

摘要:

以Nd9Fe85.5-xCoxB5.5(x=0,1,3,5)合金快淬薄带(钼辊表面速度V=35 m/s)为原料采用热压/热变形工艺制备了各向同性磁体。微观组织研究表明，含Co合金快淬薄带由大量非晶和少量α-(Fe, Co)和Nd2(Fe, Co)14B相组成，含Co量达到5at%的合金薄带中出现了亚稳相Nd3-(Fe,Co)62B14，它在随后的热压/热变形过程中分解为α-(Fe,Co)和Nd2(Fe,Co)14B；添加Co元素显著减小了热变形磁体的晶粒尺寸，软磁性相与硬磁性相的平均晶粒尺寸分别从无Co合金磁体的61，168 nm减小为含1at%Co合金磁体的24，50 nm。磁性能研究表明，与晶粒尺寸变化相对应，无Co合金以晶间静磁耦合作用为主，含Co合金以晶间交换耦合作用为主，并且随着Co含量的升高，交换耦合作用有所减弱，导致热变形磁体的矫顽力从无Co磁体的151 kA/m单调增大为含5at%Co磁体的218 kA/m。

Abstract:

Isotropic magnets were prepared by hot-pressing/die-upset process with Nd9Fe85.5-xCoxB5.5(x=0, 1, 3, 5) melt-spun ribbons as starting material at the wheel surface speed V=35 m/s. The microstructure analysis indicates that Co-doped alloy melt-spun ribbons consists of a large amount of amorphous phase and a little amount of α-(Fe, Co) and Nd2(Fe,Co)14B, and Nd3(Fe,Co)62B14 metastable phase exists in the melt-spun ribbons with x=5. The metastable phase will decomposes into α-(Fe,Co) and Nd2(Fe,Co)14B mixture during the following hot-pressing/die-upset process. The average grain sizes of both soft and hard magnetic phases decrease respectively from 61 and 168 nm to 24 and 50 nm, with the Co content increasing from 0 at% to 1at%. The magnetic property research show that corresponding to the change of grain sizes, magnetostatic coupling interaction is dominant for Co-free alloy, while exchange coupling interaction is dominant for Co-doped alloys. The effect of exchange-coupling becomes weaker with more Co-doping, resulting in the monotonous increasing of the intrinsic coercivity from 151 kA/m for Co-free magnet to 218 kA/m for 5 at% Co magnet.