Consolidation of Sm₂Fe₁₇N₃ magnets with Sm-based eutectic alloy binder

Consolidation of Sm₂Fe₁₇N₃ powder with a new Sm-based alloy as a metal binder was examined. Investigation of various Sm-based alloys led to the discovery of a Sm-Fe-Cu-Al alloy having a low melting point of 495 °C, which is more than 100 °C lower than the thermal decomposition temperature of Sm₂Fe₁₇N₃. The metallographic structure of the Sm-Fe-Cu-Al alloy ingot was a SmCu/Sm eutectic structure containing solid-solution Fe, Cu and Al. Pulverized Sm-Fe-Cu-Al powder as a binder was mixed with Sm₂Fe₁₇N₃ powder, and the mixture was hot-pressed by a current sintering apparatus. The Sm-Fe-Cu-Al alloy binder did not affect the magnetization of Sm₂Fe₁₇N₃ adversely after consolidation. The binder-added Sm₂Fe₁₇N₃ hot-pressed compacts successfully maintained the coercivity of the raw powder over a wide range of hot-pressing temperatures, whereas additive-free Sm₂Fe₁₇N₃ hot-pressed compacts showed a significant decrease in coercivity. Therefore, the Sm-Fe-Cu-Al alloy binder overcame the weakest point of Sm₂Fe₁₇N₃ magnets. XRD analysis suggested that the Sm-Fe-Cu-Al binder restrained precipitation of the α-Fe phase, which is thought to be the probable cause the decrease of coercivity.