Research On Magnetic Properties Of HDDR Isotropic NdFeB

HDDR (Hydrogenation-Disproportionation-Desorption-Recombination) is effective method for fabricating bonded magnetic powder of isotropic after rapid quenching method. Previous studies have focused on the HDDR prepared by anisotropic bonded magnetic powder, and focused on the new processing and preparing methods, while the rules about reaction condition of the HDDR prepared by isotropic bonded magnetic and influence of the hydrogen pressure was considered little, so the method of thermal analysis was introduced to study the effects of hydrogen pressure in thispaper.Parts of the preparing process of HDDR isotropic NdFeB magnetic powder was optimized firstly, which include selection of temperature and time in disproportionation phase, temperature and time in recombination phase. The research shows that in the process of disproportionation, the best condition in our experiment was 820℃and t=1.5 hours, and highest value is that (BH)m=4.1MGOe, Hcj=12.2kOe, Br=4.5kGs. In the process of recombination, the best condition in our experiment was 820℃and t=1.0 hours, and highest value is that (BH)m=3.398MGOe, Hcj=8.592kOe, Br=4.162kGs.Hydrogen pressure in the study on the reaction conditions by DTA were found that Nd-rich material and Nd2Fe14B matrix phase activates hydrogen absorption at 170℃with exothermic, heating under vacuum can increase the NdFeB alloy surface activity, reduces hydrogen absorption reaction temperature before reaction. Disproportionation peak appeared at 700℃, and products of disproportionation were NdH2+x, Fe2B and a-Fe phase. As the hydrogen pressure is increased, NdH2+x phase more stability, more conducive to disproportionation reaction, peak of disproportionation left, the temperature of reaction decreases, XRD showed that grain size calculated by Scherrer formula found that with the hydrogen pressure of disproportionation increased, the size becomes bigger. With the increase of hydrogen pressure in recombination, peak of recombination shifted to the right, the temperature of recombination increases, XRD showed that grain size calculated by Scherrer formula found that with the hydrogen pressure of recombination increased, the size becomes smaller.Recombination reaction by thermodynamic calculations and found 30kPa,820℃, 20kPa,800℃under the recombination reaction can not occur. The orthogonal test method was adopted to explore the influences of temperature and hydrogen pressure on the magnetic properties, the best condition in our experiment was 10kPa,820℃, and highest value is that (BH)m=3.89MGOe, Hcj=10.07kOe, Br=4.69kGs, best condition 20kPa,840 ℃best value (BH)m=4.47MGOe, Hcj=11.03kOe, Br=4.89kGs, best condition 30kPa,860℃best value (BH)m=3.49MGOe, Hcj=10.69kOe, Br=4.20kGs. With the increase of hydrogen pressure of recombination, the rate of recombination reaction decreased, the temperature of the best performance also increased.