Crystallization kinetics of melt-spun Nd_9Fe_(85.5-x)Co_xB_(5.5) amorphous ribbons

The heating curves of Nd9Fe85.5-x Cox B5.5(x=3%,5at%)amorphous alloy ribbons were measured by DSC protected by filling argon after vacuuming.The crystallization activation energy E,frequency factor Z,reaction rate constant K and Avrami exponent n of the two kinds of amorphous alloy ribbons were calculated according to the DSC curves.It was confirmed that the crystallization process changes from one step to two-steps with Co content increasing from 3%to 5at%.And the higher Co content in the alloy,the higher crystallization activation energy Eand crystallization reaction rate constant Kof both the initial crystallization temperature Tx and the peak one Tp.This was the reason that the increase of frequency factor Zplayes a key role.At the heating speed 10K/min,the local Avrami exponent n of Nd9Fe82.5Co3B5.5decreases sharply at first and then slow down with the increase of crystallization volume fraction x,but it rises again when x was more than 90%.It demonstrates that when x was less than 12%,the crystallization nucleation mainly in the three-dimensional nucleation mode,and it changes into the two-dimensional nucleation one when x was 12%-36%,after 36%it does in the one-dimensional nucleation one.