Directional solidification of Nd-Fe-B alloys with high temperature gradient

Directional solidification experiments were performed on peritectic Nd_13.5 Fe_79.75 B_6.75 alloy with temperature gradient of 180 K/cm and 250-360 K/cm obtained from total melting and zone melting, respectively, at pulling velocity ranging from 5 to 500 μm/s to investigate the effects on microstructure and phase constituent in the alloy. The results indicate that the microstructure of the alloy is composed of primary α-Fe dendrites, peritectic Nd₂Fe₁₄B phase and minor Nd-rich phase. The volumetric fraction of ferromagnetic Nd₂,Fe₁₄B phase is firstly increased and then decreased with rising the pulling velocity, and is improved with increasing temperature gradient. Grown at 50 μm/s, the volumetric fraction of ferromagnetic Nd₂Fc₁₄ B phase reaches up to 90% in the zone melting specimens (given a temperature gradient at 300 K/cm), which is about 30% higher than that in the total melting specimens (given a temperature gradient at 180 K/cm).