Research On Solid Solution Microstructure Evolution And Dy Doping Process Of Sintered NdFeB Under High Pressure

Sintered NdFeB permanent magnet is the most widely used and intensively researched of permanent magnets.However,there are few researches on Nd FeB sintered magnets under high pressure.Magnetic properties are expected to be improved with the researches of microstructural evolution of NdFeB sintered magnets and distribution of Dy elements in tissues under high pressure.This paper mainly studies the microscopic evolution of atmospheric pressure and 1,2,3GPa NdFeB sintered magnet organization and different process of preparation of sintered NdFeB magnets doped with Dy under high pressure.The results show that,tissues of the sintered NdFeB magnets treated by high pressure solution after normal pressure sintered became denser as the pressure increasing.The distribution of the boundary Nd-rich phase is less,and the dispersed Nd-rich phase in the matrix increases,and more strip paramagnetic phases ?-Fe are distributed along the grain boundary of matrix.Under 3GPa pressure,there are some round precipitation Nd-rich phase with higher Nd content in the large grain Nd rich dispersed phase,which never occurred in any other lower pressure.In four processes for preparing sintered NdFeB magnets doped with Dy,The magnets prepared by the three processes which are equal isostatic pressed and high pressure sintered show ferromagnetism.The content of the matrix ferromagnetic phase Nd2Fe14 B is guaranteed,and most of Dy elements exist at the grain boundaries.The subsequent500? and 900? tempering treatments make Dy to be more evenly distributed at the grain boundaries.But because of tempering,the matrix is partly transformed into paramagnetic ?-Fe.Comparing with the magnets prepared by sintered in atmospheric pressure and solution treatment in high pressure,there is more Dy distribution in grain in NdFe B doped with Dy prepared under atmospheric pressure.Dy is concentrated at the grain boundary after high pressure solid solution.The experimental results show that Dy distribution is more concentrated at grain boundaries after high pressure treatment,which not only ensures the remanence of the matrix,but also improves the grain boundary morphology and improves the coercivity.If the preparation process is further optimized,the sintered NdFe B permanent magnet with excellent coercivity and remanence is expected to be obtained.