Hot-compaction of YCo4.8Fe0.2 nanocrystals for metal-bonded magnets

Metal-bonded magnets based on the nanocrystalline YCo4.8Fe0.2 powder were produced by hot-compaction using a spark plasma-sintering device. Zn and Zn/Al metallic binders with a melting temperature close to 420 °C were employed to fabricate dense cylindrical magnets. Two different pressures were used for compaction. The higher pressure of 400 MPa provided a metal-bonded magnet with Vickers hardness (HV10) of 460 ± 20 Vickers units. The temperature coefficients for remanence (α) and coercivity (β) were derived from magnetization measurements in the temperature range 20 °C-150 °C. α and β for the Zn/Al-bonded magnet pressed with 400 MPa were −0.055%/°C and −0.201%/°C. Scanning electron microscopy revealed 'core-shell'-type microstructure. The pure YCo4.8Fe0.2 phase was detected in the core region whereas the shell was enriched with non-magnetic Zn or Zn/Al phases. High-resolution transmission electron microscope revealed the presence of ∼10 µm clusters with ∼20 nm YCo4.8Fe0.2 grains. In the Zn/Al-bonded magnet pressed at 400 MPa, the coercivity μ0Hci, remanent magnetization σ and energy product (BH)max were 0.87 T, 39.3 Am2/kg and 23.4 kJ/m3, respectively.