Study on Temperature Stability and Mechanical Properties of Sintered Nd25.5Dy6.5Co13(Fe, M)balB0.98 Magnet

Abstract

The sintered Nd_25.5Dy_6.5Co₁₃Fe_balM_1.05B_0.98 magnet (Co13 magnet) and Nd₃₀Dy_1.5Co_0.5Fe_balM_1.05B_0.98 (35SH magnet) were prepared by strip casting (SC), hydrogen decrepitation (HD), jet milling (JM), orienting compression, sintering and annealling. The maximum magnetic energy product (BH)_max and coercivity H_cj of Co13 magnet at room temperature were 30.88 MGOe and 19.01 kOe, which were lower than 35SH magnet. By adding Co and Dy, the remanence temperature coefficient α, curie temperature T_C and max operating temperature T_W were significantly increased form -0.136 %/℃ to -0.065 %/℃ (25~180 ℃), 310 ℃ to 454 ℃ and 160 ℃ to 200 ℃ respectively. Mechanical property test and fracture analysis showed that, due to the high content of Co in the magnet, the proportion of cleavage fracture in the main phase grains was increased, and the bending strength Rbb was reduced compared with 35SH magnets, which was nearly twice that of 2:17 type Sm-Co magnets. The reason for the decrease of Rbb might be that Co element preferentially replaced Fe in the 2:14:1 main phase, which led to lattice distortion and reduced the grain strength of the main phase. The microstructure analysis showed that, there was a high Co region in the grain boundary phase of Co13 magnet, and its composition was close to (Nd,Dy)(Fe,Co)₃, which might be one of the reasons for the decrease of coercivity H_cj.