Improved Understanding of the Intergranular Phases of FeNdB Sintered Magnets by Model Experiments

摘要

For a better understanding of the microstructure of the Nd-rich grain boundary phase in FeNdB sintered magnets and its influence on the improvement of the magnetic properties during post-sintering annealing, two different kinds of model investigations have been performed. By both experiments the area of intergranular phases could be increased significantly to enable comprehensive studies of thermodynamics and kinetics of the solidification products close to real processing conditions. The first experiment is carried out on as-cast pure grain boundary model samples showing two ferromagnetic intermetallic phases (of type 17:2 and 2:1) which may also occur in the grain boundaries of sintered magnets. The second experiment is coarsening the microstructure of FeNdB sintered magnets by long-term annealing at sintering temperatures to receive larger areas of the intergranular phases in triple junctions. It is found that after sintering eutectic solidification products are present in the grain boundaries which are transformed during post-sintering annealing.