Improvement of Coercivity of Nd-Fe-B Powder by Nd-Cu Sputtering

Abstract

This paper reports improvement of the coercivity of Nd-Fe-B powder by Nd-Cu sputtering. The total rare earth element content of the Nd-Fe-B powder increased by 0.8 mass% after Nd-Cu sputtering, and the sputtered Nd-Cu was observed at the surface of Nd-Fe-B powder by microstructural observation. The coercivity (H_c) of the Nd-Cu-sputtered Nd-Fe-B powder improved after annealing at temperatures above 600℃, and H_c of the sputtered powder reached a maximum value of 1312 kA m⁻¹ after annealing at 900℃. This H_c value was 470 kA m⁻¹ higher than that of Nd-Fe-B powder without sputtering. Isotropic green compacts were prepared from Nd-Fe-B powders with and without Nd-Cu sputtering, and the sputtering also improved H_c in the compacts. The compact prepared from powder with sputtering had H_c of 630 kA m⁻¹ higher than that of the compact prepared from powder without sputtering after annealing at 900℃. Microstructure observation showed that the improvement of H_c was due to an increase in the Nd-rich phase in the compact by Nd-Cu sputtering.