The Study on Thermal Expansion of Sintered Sm $_{2}$ Co $_{17}$ Magnets

Sintered Sm₂Co₁₇ magnets are widely used in aviation, spaceflight and precision instruments, etc. Thermal expansion coefficients alpha are necessary engineering data for the precision applications of the magnets (alphamacr presents the average thermal expansion coefficient). Here, we report an investigation on thermal expansion of sintered Sm₂Co₁₇ magnets. The effects of the substitutions of Gd, Dy, Er, and Pr for Sm on thermal expansion characteristics were discussed, respectively. The thermal expansion characteristics were measured using a NETZSCH DIL 402C thermal dilatometer. alpha_// is the thermal expansion coefficient in the c axis and alpha_perp is the coefficient in the base plane. All the specimens for each material were cut from the same block. A scanning electronic microscope (SEM) equipped with an energy dispersive X-ray analysis system is employed to observe the microstructure. It shows that the thermal expansion coefficient of Sm₂Co₁₇ magnets obviously exhibit anisotropy. The alpha_perp is higher than the alpha_//. The thermal expansion coefficient (both alpha_// and alpha_perp) increases and the thermal expansion anisotropy (alpha_perp-alpha_//) decreases with increasing temperature. The substitutions of heavy-rare earth elements, such as Gd+Dy, and Er decrease alphamacr_//, the substitution of Pr for Sm moderately increases alphamacr_// . The phenomenon is especially obvious in low-temperature range.