Research On Solid Penetration Dysprosium Techniques For Sintered Nd-Fe-B Magnets

Nd-Fe-B sintered magnets are widely utilized in the field of aerospace, information, communication and medical treatment, owing to their outstanding remanence, coercivity, and maximum energy product(BH)max. However, the curie temperature point is too low for applications in high temperature field such as traction motors of(hybrid) electric vehicles and wind turbines. How to develop cost-effective, low content of heavy rare earth and high temperature performance magnets become the pursuit of common goals. The dysprosium capping layer was deposited at different temperatures and time on the Nd-Fe-B surface to investigate the magnetic properties and microstructures, the mechanism of the coercivity enhancement and the change of microstructures were also studied.The magnetic properties and microstructures with different heat treatment temperature and time have been studied. The results showed that heave rare earth elements are observed in grain boundary, not in intragranular. With the increase of diffusion temperature, the coercivity of magnets have been firstly increase and then decrease. The coercivity(Hcj) of the 800℃/5h annealed was enhanced from 934kA/m to 1247kA/m by GBDP, it has been raised nearly 34%,while the remanence(Jr) decreased slightly from1.21 to 1.20 T. The diffusion depth of dysprosium in Nd-Fe-B sintered magnets increases as the annealing time prolonged, and the maximum by annealing the sample at 800℃ for 5 h, can reach at least 470 μm. The coercively(Hcj) of the 850℃/5h annealed was 724 kA/m, it is due to the coercivity of magnet gets worse as the oxygen content in grain boundary phase increasing. The grain boundary diffusion process(GBDP) using a heavy rare earth elements(HRE) such as dysprosium is known as an effective method to enhance the coercivity of Nd–Fe–B sintered magnets without reducing remanence.We discuss the low heavy rare earth and high performance Nd-Fe-B magnet by the grain boundary diffusion process(GBDP) using DyF3 coated based on detailed microstructure characterization, the results showed that the difference in coercivity may be explained by the fact that the film with the higher neodymium content exhibits a continuous Nd-rich grain boundary phase, giving better isolation of the Nd2Fe14 B grains with respect to magnetic exchange interactions. The coercivity(Hcj) of the 800 ℃/5h annealed was enhanced from 934 k A/m to 1463kA/m by GBDP, it has been raised nearly 57%,Partly of dysprosium will enter into intragranular which cause remanence decrease as increasing the heat treatment time and temperature. It is due to partial substitution of dysprosium for neodymium in sintered Nd-Fe-B magnet to enchance the anisotropy field of hard phase by producing Dy2Fe14 B.