Study Of The Grain Growth Of Nd-Fe-B Atomized Powders With Different Nd Contents And The Addition Of Nb And Ga As Doping Metals

This work presents a detailed study of grain growth annealing of gas-atomized Nd-Fe-B powders with different Nd contents, ranging from 27.5 to 31.5 wt.%. The influence of Nb or Nb-Ga additions have also been investigated. First, the microstructure of the as-atomized powders was studied and the initial grain size was measured. Grain growth annealing has been carried out at 1150 ºC for 5 hours. The addition of Nb resulted in a decrease of the final grain size due to the refining effect of Nb-Fe rich compounds and the reduced amount of free Nd to form a liquid phase. Moreover, it has been determined by Thermo-Calc simulations that Nb content in the liquid increases when the Nd content decreases, further enhancing the refining effect. In contrast, Ga addition increased the liquid formation and enhanced the grain growth kinetics, particularly in the samples with the lower Nd content.