IMPROVEMENT IN THE MECHANICAL-PROPERTIES OF PTFE BONDED ND-FE-B MAGNETS BY HEAT-TREATMENT

Rotary forging has been used to produce high density bonded magnets us ing Nd-Fe-B based melt spun ribbons (MQP-D). The binder used was polyt etrafluoroethylene (PTFE). A post-forging heal treatment at temperatur es above the crystalline melting point of PTFE (similar to 340 degrees C) has been seen to improve substantially the mechanical integrity of the compacts. Heat treatments that were undertaken in air resulted in oxidation of the magnets, but the extent of oxidation was reduced wit h increasing PTFE content, characterised by a greater retention of ma, gnetic properties. This behaviour suggests that to some extent PTFE is effective as a barrier to oxidation. By heat treating in a vacuum, an improvement of over 100% in the mechanical strength of the compacts c ould be obtained with little loss in the magnetic properties. The frac ture surfaces of both as-forged and heat treated compacts have been ex amined using scanning electron microscopy and it appears that bonding between the melt spun ribbon (MQI) and PTFE occurs during heat treatme nt.