Study on temperature stability and mechanical properties of sintered Nd_25.5Dy_6.5Co₁₃(Fe, M)_balB_0.98 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 magnet (35SH magnet) are prepared by strip casting, hydrogen decrepitation, jet milling, orienting compression, sintering and annealling. The maximum energy product (<i>BH</i>)_max and coercivity <i>H</i>_cj of Co13 magnet at room temperature are 30.88 MGOe and 19.01 kOe, which are lower than those of 35SH magnet. By adding Co and Dy, the remanence temperature coefficient α , curie temperature <i>T</i>_C, and max operating temperature <i>T</i>_W significantly increase form –0.136%/℃ to –0.065%/℃ (25–180 ℃), 310 ℃ to 454 ℃, and 160 ℃ to 200 ℃ respectively. Mechanical property test and fracture analysis show that owing to the high content of Co in the magnet, the proportion of cleavage fracture in the main phase grains increases, and the bending strength Rbb decreases compared with the Rbb of 35SH magnet, which is nearly twice that of 2∶17 type Sm-Co magnet. The reason for Rbb decreasing might be that Co element preferentially replaces Fe in the 2∶14∶1 main phase, which leads the lattice to be distorted and the grain strength of the main phase to decrease. The microstructure analysis shows that there exists a high Co region in the grain boundary phase of Co13 magnet, and its composition is close to (Nd,Dy)(Fe,Co)₃, which might be one of the reasons for coercivity <i>H</i>_cj decreasing.