Study on strengthening and toughening of sintered rare-earth permanent magnets

In recent years, we have a systematic investigation on the mechanical properties, fracture behavior and micromechanism, strengthening and toughening, and impact stability of sintered rare-earth permanent magnets (being abbreviated to “REPM”) at the aim of improving the workability and increasing the dynamic applications of REPM. A scanning electron microscope was used to study the fracture behavior and micromechanism of the experimental magnets. The impact stability of REPM was investigated using a falling-weight impact tester and an impact-acceleration standard device based on laser interference technique. The brittleness index of B=Hv∕KC was used to appraise the workability of REPM. It shows that the fracture mechanism of sintered NdFeB magnets mainly appears intergranular fracture. Sintered Sm-Co magnets tend to cleavage fracture. The fracture behavior REPM obviously exhibit anisotropy. The mechanical strength of the experimental magnets prepared by dual-alloy sintering method surpassed 390MPa without a sacrifice of magnetic properties. The impact stability increased from 2.5×104g for the ordinary magnet specimens to 11×104g for the strengthened and roughened specimens (g represents the gravity acceleration). It was found that Ti-doping decreased the Vickers-hardness Hv. Presumably, the workability of NdFeB magnets maybe improved with Ti-doping.