Crystallization kinetics, microstructure and magnetic properties of Nd₂Fe₁₄B/α-Fe magnets with Zr addition

The effects of Zr addition on the crystallization behaviour, microstructure and magnetic properties of melt-spun Nd₂Fe₁₄B/α-Fe ribbons have been studied. It is shown that the addition of Zr can prevent the formation of Nd₃Fe₆₂B₁₄ metastable phase and refine the grain sizes of α-Fe and 2 : 14 : 1 phases, thus improving the magnetic properties. Analysis of the crystallization kinetics for Nd₁₀Fe₈₄B₆ alloy suggests that the coarse-grained and heterogeneous microstructure in the Zr-free alloy is attributed to the difficult nucleation and easy growth for both the α-Fe and Nd₂Fe₁₄B grains, as well as the high decomposition temperature of the Nd₃Fe₆₂B₁₄ metastable phase. For the Zr-doped alloy, Nd₁₀Fe₈₃Zr₁B₆, the activation energy of crystallization at the initial stage of crystallization is rather low, and it increases rapidly with increasing crystallized fraction, resulting in the promotion of nucleation and restraint of grain growth.