The microstructure and magnetic properties of NdFeB magnets directly solidified at a low cooling rate

Nd12.5Fe82B5.5 ribbons have been prepared by a melt spinning technique at a wheel speed ranging from 5 to 22 m/s. It was found that the wheel speed vR dramatically influences the microstructure and magnetic properties of the ribbons. At an optimized vR, a structure with single-phase Nd2Fe14B and an enhanced coupling between grains give rise to excellent magnetic properties. For example, the coercivity, remanence ratio, and maximum energy product of the best sample quenched at a wheel speed of 13 m/s are 1227.4 kA/m, 0.76, and 182.6 kJ/m3, respectively. In comparison with the samples from under- and over-quenched conditions and all the samples with annealing, the as-quenched sample fabricated at the optimized wheel speed has the best magnetic properties.