Shoudong Mao

Evolution and effects of surface degradation layer of Sm2Co17 magnets at high temperatures

The long-term application of SmCo-based magnets at high temperatures has been restricted by the irreversible loss of magnetic properties. In this work, degradation behavior of Sm2Co17 magnets was studied at 500 °C in air and vacuum by being focused on the surface degradation layer. The structure and the composition of the degradation layer were studied experimentally, and the magnetization was calculated to certify the deduction of the irreversible loss. The soft magnetic phases in the degradation layer can result in the decline of the magnetization and the irreversible loss of magnetic properties. Furthermore, the controversial formation reason of the degradation layer was also studied. It was found that the diffusion of the oxygen, but not the sublimation of Sm, could be the dominant formation reason of the degradation layers.

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

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.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 th...