Effect of CoFeCuZr Coat on Anisotropic hermal-Expansion of the Sm_2Co_17 Magnets

摘要

The radial Sm_2Co_17 ring magnets with a CoFeCuZr coat was made by diffusing out the Sm element on the surface of the ring magnets in sintering process. The thickness of the coat can be controlled from 0.1 to 0.5 millimeter. The coat has a soft magnetic properties(sigma_s=152emu/g, _iH_c=57Oe) and better toughness. The composition of the coat is 64.4Co, 28.7Fe, 4.6Fe, 4.6Cu and 2.3Zr (at percent). A transition region (at least one millimeter)deviated from the Sm_2Co_17 matrix composition is formed between the coat and the matrix. The difference of thermal-expansion of the magnet with the coat is reduced on parallel and perpendicular to the magnetizing orientation. From room temperature to 800 deg C, the average thermal-expansion coefficients alpha with the coat are 136.6(perpendicular) and 100.6(//)X10~-6/deg C (alpha_perpendicular-alpha_//=36), and the alpha values without the coat are 155.7(perpendicular) and 122.6(//)X10~-6/deg C(alpha_perpendicular-alpha_//=43.1). The radial Sm_2Co_17 ring magnet (phi 49 X phi 44 X 2.5mm) was obtained after cutting off CoFeCuZr coat. The magnetic properties is Br=10.2kGs, _iH_c=13.5kOe, (BH)_max=22.5kMGOe.