Microstructure evolution of Nd_13.5Fe_79.75B_6.75 peritectic alloy under laser rapid solidification

Laser rapid solidification experiments were performed on Nd_13.5Fe_79.75B_6.75 hyperperitectic alloy to investigate microstructure evolution. The results show that at scanning velocity higher than 2 mm/s, peritectic T1 phase directly precipitates from the liquid instead of by peritectic reaction. Using KGT model and the maximum growth temperature criterion, critical velocity for the transition from primary γ-Fe phase to T₁ phase is calculated to be 0.34 mm/s, which approaches the experimental value of 2 mm/s. High velocity banding structure, showing oscillatory plane front and cellular microstructures, is firstly detected in Nd_13.5Fe_79.75B_6.75 peritectic alloys. The growth velocity for banding structure is deduced to be in the range of 100-500 mm/s. The experimental appearance of the banding structure agrees well with the theoretical prediction.