Inducing magnetic anisotropy and optimized microstructure in rapidly solidified Nd–Fe–B based magnets by thermal gradient, magnetic field and hot deformation. (5th October 2016)

• Record Type: Journal Article
• Authors: Zhao, L Z; Li, W; Wu, X H; Hussain, M; Liu, Z W; Zhang, G Q; Greneche, J M
• Is Part Of: Materials research express. Volume 3:Number 10(2016)
• Publication Date: 2016-10-05
• Subjects: Nd–Fe–B -- hard magnet -- direct casting -- magnetic anisotropy -- thermal gradient -- magnetic field -- hot deformation; Materials science -- Research -- Periodicals; Materials science -- Periodicals; 620.11
• DOI: 10.1088/2053-1591/3/10/105001
• Languages: English
• ISSNs: 2053-1591

Abstract

Abstract: Direct preparation of Nd–Fe–B alloys by rapid solidification of copper mold casting is a very simple and low cost process for mini-magnets, but these magnets are generally magnetically isotropic. In this work, high coercivity Nd24 Co20 Fe41 B11 Al4 rods were produced by injection casting. To induce magnetic anisotropy, temperature gradient, assisted magnetic field, and hot deformation (HD) procedures were employed. As-cast samples showed non-uniform microstructure due to the melt convection. The thermal gradient during solidification led to the formation of radially distributed acicular hard magnetic grains, which gives the magnetic anisotropy. The growth of the oriented grains was confirmed by phase field simulation. A magnetic field up to 1 T applied along the casting direction could not induce significant magnetic anisotropy, but it improved the magnetic properties by reducing the non-uniformity and forming a uniform microstructure. The annealed alloys exhibited high intrinsic coercivity but disappeared anisotropy. HD was demonstrated to be a good approach for inducing magnetic anisotropy and enhanced coercivity by deforming and refining the grains. This work provides an alternative approach for preparing fully dense Nd-rich anisotropic bulk Nd–Fe–B magnets.