GENESIS OF THE CELL MICROSTRUCTURE IN THE SM(CO, FE, CU, ZR) PERMANENT-MAGNETS WITH 2 17 TYPE/

The alloys with composition around Sm11.5Co58.4Fe22.5Cu5.3Zr2.4 (at%) present hard magnet properties when their microstructure consists of a network of cells based on Sm-2(Co, Fe)(17), limited by boundaries bas ed on Sm(Co, Cu)(5) and cut by platelets based on (Sm, Zr)Co-3. The ge nesis of this microstructure is studied by transmission electron micro scopy of heat-treated specimens. The fractions and compositions of the phases formed are evaluated from atomic balance equations. The micros tructure forms by nucleation growth of ordered R2:17 cells in the 1:7 matrix, then by nucleation of 1:3 platelets on the twin boundaries in R2:17. The processes are likely limited by diffusion.