Abstract:Microstructure and magnetic properties of Sm(Co_balFe_0.108Cu_0.131Zr_0.042)_7.0 annealed at 830 ℃ for 10-30 h have been systematically investigated by means of transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and magnetic measurement. It is found that the heat-treated alloy consists of the rhombohedral Sm₂Co₁₇ phase as the cell and the hexagonal Sm(CoCu)₅ as the cell boundary phases. In addition, the structure contains Zr-rich plate-like phase on the basal planes, running across both the cells and cell boundaries, as well as Zr-rich Sm(CoCuFeZr)_x precipitates. It is obvious that the annealing time significantly affects the microstructure. With increasing the annealing time from 10 h up to 30 h, the Sm₂Co₁₇R cell size increases from 80-110 nm to 150 nm and becomes uniform, the density of platelet phase and the content of Sm(CoCuFeZr)_x precipitates also increase. The Cu-rich SmCo₅ sell boundary phase and Zr-rich Sm(CoCuFeZr)_x precipitates are responsible for the high coercivity at both room and high temperature. Magnetic analysis shows that the remanence B_r enhances from 0.625T to 0.845T with the annealing time increasing from 10 to 30 h. The intrinsic coercivity H_ci reaches the maximum value of about 2417.9 kA/m at room temperature and 693.5 kA/m at 500 ℃ after annealing for 20 h.

Key words: Sm₂Co₁₇-based high temperature permanent magnet; annealing treatment; precipitate; cellular structure