Effect of Cu and Ti additions on the microstructures and magnetic properties of Nd₈Fe₈₆B₆ nanocomposite magnets

The microstructure and magnetic properties of Nd₈Fe₈₆B₆ nanocomposite magnets with combined Cu and Ti additions prepared by melt spinning have been investigated. The results show that Cu can enhance the nucleation kinetics of α-Fe phase, while Ti can hinder the crystallization kinetics of α-Fe phase. For pure ternary NdFeB and a single Cu addition NdFeBCu ribbons, the α-Fe phase precipitates directly from amorphous and its grains grow quickly during crystallization. But for the NdFeBCuTi ribbons with combined Cu and Ti additions, a metastable hexagonal phase with TbCu₇-type structure is formed prior to α-Fe and quickly decomposed to Nd₂Fe₁₄B and α-Fe phases during crystallization. At the same time, the growth of α-Fe grains is suppressed, which is propitious to form the more uniform microstructure with fine soft α-Fe grains and enhance the magnetic properties. The optimal magnetic properties _JH_c = 4.6 kOe, σ_r = 102 emu/g, (BH)_max = 13 MGOe can be obtained after annealed at the temperature of 650°C for 10 min.