Cryogenic Processing Of Sintered Ndfeb Modified

Presently, sintered Nd-Fe-B magnet has been used in every field. This is important to study its superior magnetic property, meanwhile there are many scholars to research the mechanical properties of the magnet. However, the scholars don't change the brittle characteristics of the magnets. Currently, we always add some elements to improve the magnetic properties and mechanical properties of the sintered Nd-Fe-B magnets, but the way of the subzero treatment to study the sintered Nd-Fe-B magnet is much less. There are two reasons: first, the equipment and condition of cryogeny is hard; second, the effect of the black metal with subzero treatment is clear, but this is the episode of explore to study the effect of the other materials. Then the magnets and powders of the brands of N35,N45,35H,42H are putted into the cryogenic box, from the room temperature(25℃) down to -175℃by the speed of 8℃/min, and keep the temperature of -175℃with 4h, increase to the room temperature in the box at last. To understand the change of the magnetic properties and mechanical properties of magnets after the subzero treatment, and the effect of sintered Nd-Fe-B magnet with the cryogenic treatment. So this is our works:1.To test the magnetic properties of the magnets by the permanent magnet detector of the NIM-1000 model, we find remanence and maximum energy product are all increase, while the intrinsic coercive force of some magnets are increase, the others are decrease. The three kinds of the magnetic parameter of the brand N45 are all increase.2.To analyze the distribution of the particle size of the magnetic powder. We find the particle sizes of the magnetic powders are bigger than before. The XRD analysis shows that the volume fraction of the percentage of the main phase is increase, and some non-magnetic phases and the soft magnetic phases are able to change. The analysis of the microstructure shows that the number ?of the holes is much lower, the number of the rich-Nd pellets with on to the grain's surface are much more.3.To test the hardness and the bending strength of the four kinds of magnets with subzero treatment, we find that the hardness of the magnets is decrease, except the hardness of N35, and the improving of the bending strength is not patency, the stress of the 42H magnet is much better than others, up to 6.9%.4.The microstructure of the ruptured magnet is observed through SEM. It is obviously the fracture mechanism is the rupture of the typical brittle nature. There are three kinds of fracture mechanism: a,the crack expand in the rich Nd phase; b,the crack extend the interface of the magnetic phase and rich-Nd phase;c,the crack extend from the particles of rich-Nd phase.Through these experiments, we are able to improve the magnetic properties of sintered NdFeB by the deep cryogenic treatment, and the magnet is still brittleness, but it can increase the values of the bending strength.