1.6.8.4.2 Sintered Magnets VACUUMSCHMELZE（1.6.8.4.2烧结磁体VACUUMSCHMELZE）.pdfVIP

.2 Sintered Magnets Sintered magnets are manufactured by powder metallurgy in many shapes and dimensions in large volumes. Besides hardmagnetic hexaferrites and Alnico materials, see Alnico and Hexaferrites (), mainly Rare Earth (RE) – Transition Metal (TM) alloys are applied. By powder metallurgy the magnetocrystalline anisotropy of hard hexaferrites, of Samarium (Sm) – Cobalt (Co) compounds, SmCo as well as modified Sm (Co,Cu,Fe,Zr) , and of the 5 2 17 Neodymium (Nd)–Iron (Fe)-Boron (B) compound, Nd2Fe14B, can be exploited in order to achieve anisotropic magnets with a high remanent polarization BR and a strong corecivity HcJ, see Rare Earth Magnetic Materials (.1). The basic principles of the production route, in particular the benefits of the different powder compaction processes and their impact on the dimensions and on the magnetic properties are reviewed. 1. Alloying and Powder Processing Nd-Fe-B or Sm-Co alloys can be prepared from RE metals, mainly Nd and Sm or others, transition metals, Fe or Co, and master-alloys Fe-B, Fe-Nb, or additions, e. g. Al, Cu, Zr, etc. Since the RE metals are very reactive, alloying has to be performed in a vacuum induction furnace. The melting cycle needs careful optimization in order to minimize chemical reactions with the crucible and to prevent oxidation by residual atmospheric gases. The melted alloy is cast into ingots which have a polycrystalline microstructure, see top of Fig. 1. An alternative alloying route is the calciothermic reduction diffusion (RD) process (Herget 1985). RE-oxides, TM-powder and the required additions are mixed with Ca-granulate as a reducing agent. The compacted powders are heated in vacuum up to 1100 °C, so that the Ca- vapor reduces the RE-oxide to