The Effect Of Refractory Element Ti On The Nanocomposite Nd₂Fe₁₄B/α-fe Magnetic Powders

Nanocomposite permanent magnetic materials are a sort of remarkable materials, which combine the high anisotropic field of hard magnetic phase and the large saturation magnetization of soft magnetic phase. The exchange coupling interaction between two phases provides the magnet desired magnetic properties.It has been demonstrated by micromagnetic models that the theoretical value of the maximum energy product can reach1MJ/m3, which is much higher than that of other uncoupled permanent magnets. Besides, some other merits, like low content of rare earth and high chemical stability, provide this material a bright prospect.Firstly, we researched the effect of wheel velocity on nanocomposite Nd8Fe86B6ribbons. To be specific, we mainly discussed the influence of microstructure in as-quenched ribbons, like initial grain size and content of amorphous phase, on magnetic properties of the annealed ribbons. The result showed that18m/s was the optimal velocity, at which the annealed Nd8Fe86B6ribbons obtained the optimized magnetic properties. Due to the large initial grains and the reduced heterogeneous nucleation sites respectively, both the fully crystalline structure and inordinate content of amorphous structure have adverse effects on the precipitation progress of a-Fe, leading to the a-Fe grains coarsening which weakens the exchange coupling interaction and deteriorates the magnetic properties.Secondly, we researched the effect of Ti on microstructure and properties of nanocomposite NdFeB ribbons. At first we prepared different ribbons at18m/s from Nd8Fe86-xTixB6(x=0-2) alloys. It shows that the Ti improves the glass forming ability obviously. From the DSC result, we find that adding Ti changes the annealing progress from one-step one, in which2:14:1phase and a-Fe phase precipitate directly from amorphous phase, into two-step one in which a sort of transition phase precipitate firstly and decompose into2:14:1phase and a-Fe phase then. According to many related work, this transition phase is a TbCu7-type metastable phase of which the nominal composition is Nd2Fe17Bx(x=0-1). After a serias of heat treatment on different as-quenched ribbons, we obtained the optimized magnetic properties of different ribbons respectively. It shows that the Ti can refine the grains effectively and improve the coercivity. Since Ti is non-magnetic element, the additive amount should be limited.Thirdly, we also researched the effect of the TbCu7-type metastable phase precipitation on nanocomposite ribbons. At first, we prepared a serias of ribbons at different wheel velocities from Nd8Fe8.5Ti1.5B6alloy. From the DSC result, we find that the annealing progress become a three-step one for the ribbons prepared at high velocity. After a serias of heat treatment on different ribbons, the specific progress is determined, which contains TbCu7-type metastable phase precipitation, metastable phase reacting with amorphous phase to form2:14:1phase and the decomposition of metastable phase. Last, with the calculation of crystallization activation energy, we systematically analysed the effect of annealing progress on the magnetic properties of nanocomposite ribbons. The optimized properties(Br=8.1kGs, Hcj=6.4kOe,(BH)max=9.7MGOe) were obtained for the Nd8Fe84.5Ti1.5B6ribbons prepared at14m/s.