Development of highest grades of NdFeB sintered magnets

New applications and designs using sintered NdFeB permanent magnets are driven by the improvement of the magnet's intrinsic magnetic properties, thermal stability and corrosion resistance. Both magnet composition and microstructure are the key to maximizing these properties, and they are strongly affected by the powder production process, the resulting particle size distribution and the heat treatment cycles. Two main aspects of the powder production have been investigated: the generation of a very narrow particle size distribution, and the utilization of a two-alloy route with controlled distribution of the elements. Both improvements resulted in the achievement of a record combination of intrinsic magnetic properties with excellent corrosion resistance. The alignment degree obtained with isostatic compaction has been more than 98%. Control of the microstructure of the grain boundary phase through heat treatment results in the development of high coercivity for both single and two alloy routes. Magnets with high remanence and energy product have been produced with sufficient coercivity to be practically used in magnetic circuits up to 100 degreesC with a B/-mu(0)H > 1. The following magnetic properties have been achieved using, respectively, a narrow particle size distribution with the single alloy route, and controlled distribution of elements with the two-alloy route: B-r: 1.461 T (14.61 kG), H-cJ: 1043 kA/m (13.04 kOe), (BH)(max): 411 kJ/m(3) (51.43 MGOe) B-r: 1.412 T (14.12 kG), H-cJ: 1297 kA/m (16.21kOe), (BH)(max): 383 kJ/m(3) (47.93 MGOe) The intrinsic corrosion resistance of both types is excellent; less than 0.1 mg/cm(2) weight loss after a cyclic Pressure Cooker Test (PCT) at 120degreesC, 2 bar, and 50 hours.