Sintered Nd–Fe–B magnets with high strength

Abstract The effect of boron variation in the minor addition of grain-boundary alloys on the mechanical properties and microstructure of sintered Nd–Fe–B magnets has been studied. It shows that the bending strength of most magnets with minor grain-boundary alloy additions is much higher than that of the magnet prepared by the single alloy. The maximum of the former reached 397 MPa, which was higher than the bending strength of cast/hot-rolled magnets. The latter was only 309 MPa. Minor additions of the grain-boundary alloys made the distribution of grain-boundary phase more uniform so that the phenomena of the direct contacts between main-phase grains nearly disappeared. The irregular grain growth was restrained. This is also one of the reasons that the magnets with minor grain-boundary alloy additions have possessed higher bending strength. In addition, the phase analyses indicated that the reduction of crystal structure anisotropy probably helps to increase bending strength. The study results also show that minor additions of the grain-boundary alloys do not almost affect the magnetic properties of sintered Nd–Fe–B magnets. It suggests that slightly adding grain-boundary alloys and properly adjusting its composition can substantially increase the bending strength of sintered Nd–Fe–B magnets without a sacrifice of magnetic properties.