FABRICATION OF ND-FE-B/ALPHA-FE NANOCOMPOSITE MAGNETS BY SHOCK COMPACTION AND HEAT TREATMENT OF MECHANICALLY MILLED POWDERS

Bulk nanocomposite magnets based on the Nd-Fe-B/alpha-Fe system were fabricated using mechanical alloying and shock compaction. A high energy ball mill was used to combine Magnaquench MQA-T type Nd-Fe-B powder with varying amounts of pure Fe powder. The mechanically milled powders were shock compacted to near full density at a primary shock pressure of approximately 6.3 GPa. A range of heat treatments were applied to the recovered samples, and the crystallization behavior and magnetic properties were measured. The presence of additional iron increases magnetization saturation, but decreases coercivity. Heat treatment at 550 degrees C increases the coercivity only marginally, which can be attributed to the amorphous material crystallizing to the alpha-Fe phase instead of the Nd2Fe14B phase. A subsequent shock experiment at 8.3 GPa produced a tetragonal to BCC phase transition in the Nd-Fe-B powder.