Abstract
The Nd7Y2.5Fe64.5Nb3B23 nanocomposite permanent magnets in the form of rods with 2 mm in diameter have been developed by annealing the amorphous precursors produced by copper mold casting technique. The phase evolution, structure, magnetic and mechanical properties were investigated with X-ray diffractometry, differential scanning calorimetry, electron microscopy, magnetometry and universal uniaxial compression strength techniques. The heat treatment conditions under which the magnets attained maximum magnetic and mechanical properties have been established. The results indicate that magnet properties are sensitive to grain size and volume content of the magnetic phases present in the microstructure. The composite microstructure was mainly composed of soft alpha-Fe (20-30 nm) and hard Nd2Fe14B (45-65 nm) magnetic phase grains. The maximum coercivity of 959.18 kA/m was achieved with the magnets annealed at 760 degrees C whereas the highest remanence of 0.57 T was obtained with the magnets treated at 710 degrees C. The optimally annealed magnets possessed promising magnetic properties such as H-j(c) of 891.52 kA/m, B-r of 0.57 T, M-r/M-s = 0.68, (BH)(max) of 56.8 kJ/m(3) as well as the micro-Vickers hardness (H-v) of 1138 +/- 20 and compressive stress (sigma(f)) of 239 +/- 10 MPa. (C) 2011 Elsevier B. V. All rights reserved.