Excellent magnetic and mechanical properties of the Sm2Co17-based magnets fabricated via microwave processing

Abstract

The development of high performance Sm2Co17-based permanent magnets (SCPMs) by employing efficient fabrication methods can be beneficial for many applications. In this study, we prove that Sm(CobalFe0.25Cu0.06Zr0.02)7.5 PMs with an improved energy product (BH)max (27.1–30.0 MGOe) and bending strength (168.2–177.5 MPa) can be achieved by using microwave (MW) ageing. During short-time MW-ageing at 840 °C for 1 h, phase separation was performed in the hexagonal Sm2Co17 (2:17H) supersaturated solid solution characterized with small wavelength of composition modulations (λ = 1–2 nm) and high density of pure-edge dislocations. This contributes to large gradient energy ΔGγ and high separation rate, thus results in the formation of 20-nm uniform nanoparticles. The nanoparticles grow into a homogeneous 50-nm cellular structure composed of rhombohedral Sm2Co17 (2:17R) cells and hexagonal SmCo5 (1:5H) cell boundaries after being MW-aged for 3 h, then the non-uniform grain growth to 80 nm takes place by further increasing the time to 5 h. Moreover, prolonging the ageing time from 3 to 5 h can increase the Cu enrichment in the 1:5H cell boundary phase and enhance the coercivity Hci from 17.4 to 23.1 kOe. As compared with conventional ageing, the MW ageing considerably reduces the ageing time and the MW-aged PMs exhibit finer and more homogeneous cellular structures.