Research On HDDR Process For High Performance NdFeB Magnetic Powder

With the increasing application of NdFeB magnetic materials in mobile communication,equipment manufacturing,aerospace and other fields,it has become one of the basic materials in the manufacturing industry.Countries around the world have invested huge manpower and material resources in the research and development of magnetic materials,especially NdFeB magnetic materials.At present,the focus of research in various countries is how to improve the performance of magnets without adding heavy rare earths such as Dy and Tb.After years of research,the most effective method is to reduce the grain size of NdFeB powder without being oxidized.The main method is HDDR process.However,due to the lack of special equipment and the unstable performance of the prepared magnetic powder,the HDDR process for preparing NdFeB magnetic powder stays at the laboratory level.The HDDR processing equipment used in this article is a rotary hydrogen furnace.The raw materials are the industrial production of ingots for bonded magnets and quick-set sheets for sintered magnets.The specific research results are as follows:?1?Preparation of NdFeB magnetic powder from NdFeB ingot casting by HDDR process.The hydrogen pressure,temperature,dehydrogenation recombination temperature and hydrogen pressure were changed in turn.The effect of process parameters on the orientation,grain size and Nd-rich phase distribution of the magnetic powder was studied to find the best process parameters.The best HDDR process of Nd-Fe-B ingot casting is as follows:hydrogenation disproportionation hydrogen pressure is 50 k Pa,hydrogenation disproportionation temperature is 820?,dehydrogenation recombination temperature is 860?,dehydrogenation recombination hydrogen pressure is 3 k Pa,the best magnetic properties of magnetic powder are B_r=7.775 k Gs?H_cj=14.679kOe??BH?_max=10.594 MGOe??2?On the basis of the above experimental study,the dehydrogenation recombination temperature and hydrogen pressure were changed in turn in the HDDR treatment process of NdFeB strip casting.Compared with the original ingot casting,the orientation of the grains of strip casting is stronger.After the HDDR process,the grains of the magnetic particles grow along the columnar structure of the original strip casting,the grain size is smaller and the distribution is more uniform.However,the magnetic properties of the different particle sizes differ greatly after the HDDR process.On the one hand,the components of the larger particles are more uniform,after the HDDR process,new main phase of Nd₂Fe₁₄B can be completely formed.On the other hand,the particles with larger particle size are easier to inherit the crystal orientation of the original strip casting.The best HDDR process of Nd-Fe-B strip casting is as follows:the temperature of dehydrogenation recombination is 860?,the pressure of dehydrogenation recombination hydrogen is 3 k Pa,and the best magnetic properties of magnetic powder are B_r=6.915 k Gs?H_cj=15.174 k Oe??BH?_max=9.324 MGOe.