On the coercivity of melt-spun (Fe, M)-Nd-C alloys (M=Cu, Al, Co, and Ni)

The influence of small additions (less than or equal to 2.0 at.%) of Cu, Al, Co, and Ni on the microstructural development and the coercivity of melt-spun Fe-Nd-C alloys was investigated. Addition of these elements tended to crystallize the as-spun ribbons. While Cu preferred to stabilize the crystallization of alpha-Fe, other elements, especially Al, preferred to stabilize the crystallization of Fe17Nd2Cx. The average grain size of Fe14Nd2C (0.1-0.3 mu m) obtained by a proper annealing in the ribbon treated with 0.5 at.% additive was much finer than that of additive-free ribbons, which would be the major source of the large increase in coercivity. Among the additives, Cu and Ni were very effective in increasing the coercivity. By adding 0.5 at.% Cu or Ni, intrinsic coercivities of more than 1.4 T, which were 40-50% higher than that (similar to 1.0 T) of additive-free ribbons, could be obtained after annealing at 750-800 degrees C.