Influence of Ce Content on the Mechanical Properties of Sintered (Ce, Nd)–Fe–B Magnets

The (R,Ce)-Fe-B magnets have been successfully industrialized in recent years. The mechanical property of sintered permanent magnets is one important aspect of their comprehensive performances, which directly influences the service reliability and the production cost. In this paper, the bending strength, fracture toughness, Vickers hardness, and brittleness index of commercial (R _1-x Ce _x ) _30.5-31.5 Fe _bal. B ₁ M ₁ magnets with different cerium contents have been investigated. The micro-fractures of the magnets were observed by a scanning electron microscopy equipped with energy dispersive X-ray analysis system. It shows that the bending strength and the fracture toughness of (R,Ce)-Fe-B magnets have a downward tendency with increasing Ce content x, while the Vickers hardness of the magnets varies irregularly with Ce contents in this paper. The optimum mechanical properties have been obtained in the (R _1-x Ce _x ) _30.5-31.5 Fe _bal. B ₁ M ₁ magnet with x = 0.15; the bending strength, fracture toughness and brittleness index of the magnet with x = 0.15 are obviously superior to those of the ordinary sintered Nd-Fe-B magnets. Some flocculent oxide phases have been discovered in the (R,Ce)-Fe-B magnet with x = 0.15. The flocculent phases may absorb the crack propagating energy, and reduce the stress concentration at a crack tip, which is beneficial to strengthening and toughening of (R,Ce)-Fe-B magnets. However, the mechanical properties are obviously worse for the magnet with x = 0.45(Ce/ΣRE = 45%). That is probably because the microstructures of the magnet with x = 0.45 become deteriorated, in which abnormally large grains have been observed.