Study on the Crystallization Kinetics of Ti-doped Nd2Fe14B/α-Fe Nanocomposite Permanent Magnets

Nanocomposite magnets consisting of a fine mixture of magnetically hard and soft phase have attracted much attention for potential permanent magnet development. One of the important requirements for alloys to exhibit excellent magnetic properties is a nanocrystalline grain size. The soft and hard magnetic phases can simultaneously achieve ideal nanoscale composites. The effect of Ti additions on the amorphous crystallization process of the exchange-coupled nanocomposite Nd2Fe14B/α-Fe magnets prepared by melt spinning has been investigated. The results show that Ti can change the crystallization kinetics of the NdFeB melt-spun ribbons. Ti can increase the activation energy of α-Fe and contrarily decrease the activation energy of a metastable 1:7 phase, so the growth speed of α-Fe reduces and the metastable 1:7 phase can stably precipitate from amorphous. When the annealing temperature is increased, a metastable 1:7 phase is decomposed into the α-Fe and Nd2Fe14B phase. The microstructure observation shows that the grains of the alloys doped with Ti are fine and uniform, with an average grain size of about 20 nm, and no particularly large α-Fe particles appear. Both the magnetic properties and the exchange coupling between the soft and hard magnetic phases are enhanced in the obtained nanocomposite magnets. The optimal magnetic property of Ti addition is (BH)max=12 MGOe. The significant improvements of magnetic properties originate from the microstructure with fine grains and uniform distribution by introducing Ti element.