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 hotcompaction using a spark plasma-sintering device. Zn and Zn/Al metallic binders with a melting temperature close to 420 degrees 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 (alpha) and coercivity (beta) were derived from magnetization measurements in the temperature range 20 degrees C-150 degrees C. alpha and beta for the Zn/Al-bonded magnet pressed with 400 MPa were -0.055%/degrees C and -0.201%/degrees 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 similar to 10 mu m clusters with similar to 20 nm YCo4.8Fe0.2 grains. In the Zn/Al-bonded magnet pressed at 400 MPa, the coercivity mu H-0(ci), remanent magnetization sigma and energy product (BH)(max) were 0.87 T, 39.3 Am-2/kg and 23.4 kJ/m(3), respectively. (C) 2018 Elsevier B.V. All rights reserved.