The Investigation Of High Performance Ndfeb Powders Produced By Hddr Technique

With the rapid development of modern industry, Electrification revolution and the information revolution followed one by one, the development and application of high-performance bonded NdFeB has broad prospects. One of the most important means to prepare bonded NdFeB is HDDR(hydrogenation-disproportionation-desorption-recombination)technique, which has now become a hot spot because of its simple technology process and equipment, homogeneous magnetic properties of powders, lower cost, fewer investment and higher efficiency.In this experiment we did the research on the influence of different stages of HDDR technique on the magnetic properties of the four alloy composition below: Nd12.5Fe80.4-XCoXGa0.5Zr0.1B6.5(X=0,4,8,12,15),Nd12.5Fe68.9-XCo12GaXZr0.1B6.5(X=0,0.1,0.3,0.5),Nd10.5Dy2Fe69-XCo12NbXB6.5 (X=0,1,2,3),Nd12.5-XGdXFe68.8 Co12Ga0.2B6.5(X=0,0.05,0.1,0.15), and studied the effect of the additional elements (Co,Ga,Nb,Gd) on the magnetic properties. In this experiment HDDR technique is divided into two parts:HD and DR, and HD is further divided into two stages:low temperature stage and high temperature stage. The phase changes of NdFeB alloy through HDDR technique are shown below:in original casting ingot there is big NdFeB phase(about 64.346μm), after HD process the 2:14:1 phase is disproportionationed into the next three phase:NdH2,α-(Fe,Co)å'Œ(Fe,Co)2B, and after HDDR technique, the three disproportionation products are recombined into fine NdFeB phase(about 0.486μm).Through the research on HD part, we find there is little influence on the magnetic properties by changing temperature of HD's low temperature stage; And hydrogen pressure has more influence, and first increases then reduce in trend, when the pressure reaches 0.09MPa, the properties are best.HD's high temperature stage has significant effect, and among the parameters, the hydrogen pressure plays the most important role, when the pressure reaches between 0.025～0.035MPa, the magnetic properties are better; and the best disproportionation's time and temperature is 820℃×2.5～3h.Through the research on DR part, we find the reaction rate of HD stage has big influence on the magnetic properties, the best DR process is usually 820～830℃×x 0.25～0.5h×high vacuum, and the best DR process of alloy with Nb and Dy is 820℃×0.5h×low vacuumThe additional element Co is helpful for the whole properties and anisotropy's improvement, and when content of Co reaches 15 percentages, the properties are best. When the next process is taken:25℃×0.09MPa×1hâ†'820℃×0.025MPa×2.5hâ†'820℃×high vacuum×0.5h, the magnetic properties of Nd12.5Fe80.4-XCoX Ga0.5Zr0.1B6.5 alloy can reach: (BH)m=254.64kJ/m3, Br=1.252T,jHc= 772.8kA/m, DOA=0.578.The additional element Ga is helpful for the improvement of jHc,(BH)m and anisotropy, and when the content reached 0.3 percentages the properties are best. When the following process is taken:25℃×0.09MPa×1hâ†'820℃×0.035MPa×3hâ†'830℃×low vacuum×0.25hâ†'830℃×high vaccum×0.25, the permanent magnetic properties of Nd12.5Fe68.9-XCo12GaXZr0.1B6.5 can reach:(BH)m=218.24kJ/m3, jHc=851.2kA/m, Br=1.217T, DOA=0.352。The additional element Nb can obviously advance the alloy's coercive force, but Br,(BH)m and anisotropy is significantly reduced, and when the content reaches 1 percentage the coercive is best. When the following HDDR technique is taken:25℃×0.09MPa×1hâ†'820℃×0.035MPa×3hâ†'820℃×low vaccum×0.5h, the magnetic properties of Nd10.5Dy2Fe69-XCo12NbXB6.5 can reach:(BH)m=73.6kJ/m3, jHc=1229.6 kA/m, Br=0.871T, DOA=0.053.The additional element Gd can absolutely reduce the whole magnetic properties of Nd12.5-XGdXFe68.8Co12Ga0.2B6.5 and is bad for the anisotropy.