Grain boundary diffusion of magnetron sputter coated heavy rare earth elements in sintered Nd-Fe-B magnet

• Published in: Journal of applied physics Vol. 123; no. 24
• Main Authors: Wu, Binghui, Zhang, Qingke, Li, Weidong, Ding, Xuefeng, Yang, Lijing, Ghafar Wattoo, Abdul, Zhang, Lijiao, Mao, Shoudong, Song, Zhenlun
• Format: Journal Article
• Language: English
• Published: Melville American Institute of Physics 28.06.2018
• Subjects: Applied physics; Coercivity; Corrosion resistance; Diffusion coating; Diffusion rate; Direct current; Dysprosium; Electrochemical analysis; Ferrous alloys; Grain boundaries; Grain boundary diffusion; Iron; Magnetic materials; Magnetic properties; Magnetron sputtering; Magnets; Neodymium; Protective coatings; Rare earth elements; Sintering; Sputtered coatings; Trace elements
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.5023092

The diffusion of Tb or Dy heavy rare earth elements (HREEs) coated on sintered Nd-Fe-B magnets by a direct current (DC) magnetron sputtering and its influences on microstructure, magnetic properties and electrochemical properties of the magnets were investigated. The results reveal that the HREE diffuses into the magnet and substitutes some of the Nd to form a (Nd1-x,HREEx)2Fe14B shell. The HREE concentration along the direction perpendicular to the sputtered coating surface shows a dual-trend distribution, which was considered to be induced by a fast diffusion in the grain boundary phase and a slow diffusion in the grain phase. The diffusion of DC magnetron sputtered metallic Tb or Dy shows higher efficiency of HREE consumption and greater gain of the coercivity compared with diffusion sources prepared by some other coating methods or consisted of HREE compounds. The coercivity increases from 14.6 kOe for a 5 mm thick original specimen to 24.0 kOe and 19.5 kOe for the Tb and Dy diffused specimens when the coating thickness on a double surface of the specimen is about 12.0 μm. The HREE-diffused magnets also show better corrosion resistance. At the request of the authors, this article is being retracted effective 8 July 2019.