Effect of wheel speed on the crystallization behavior of as-quenched Nd-Fe-B alloys

Abstract

A series of alloys composed of Nd9Fe85Nb0.5B5.5 were prepared through rapid quenching by different wheel speeds. Nanocomposite was usually obtained by subjecting the as-quenched alloys to a crystallization annealing. The crystallization behavior was investigated by differential scanning calorimetry (DSC) as the primary method. The results showed that the DSC curve of sample prepared at 15 m/s had only one exothermic peak at about 690 °C. When the wheel speed increased to 18-27 m/s, one more peak at 590 °C appeared. Moreover, the intensity of this new peak enhances while the original one at 690 °C declined as the speed increases within this range. When the speed further grew up to 30, 35, or 40 m/s , only the peak at 590 °C remained while the other disappeared. This could be ascribed to the different initial phase structures of the alloys, which were found to vary with the wheel speeds. As can be seen, with increasing the wheel speed, the contents of amorphous and metastable phase increased while Nd2Fe14B phase decreased. This change resulted in a huge effect on the crystallization behavior. We could deduce the relative content of each phase from the integral areas of peaks in DSC curves in different samples and figure out the phase transition in the crystallization. The results showed that the crystallization of samples prepared by relatively high speeds, which are almost amorphous initially, manifest as only one step, while those prepared by relatively low speeds showed two. Subsequently, we analyzed the crystallization process and interpreted it from the theory of energy barrier.

Nanocrystalline and nanocomposite permanent magnets by melt spinning technique

“…Men et al prepared a set of ribbons with different initial phase structure, i.e., amorphous, TbCu 7 -type Nd 2 Fe 17 B x , α-Fe, and their mixture, by varying wheel speed from 15 to 40 m/s. [43] They used the theory of energy barrier to interpret the crystallization process, as schematized in Fig. 8.…”

“…(color online) The crystallization mechanism of as-quenched ribbons with different initial phase structure. ∆H 1 , ∆H 2 , and ∆ H 3 are the enthalpy change of the reactions: (1) amorphous → Nd 2 Fe 17 B x , (2) Nd 2 Fe 17 B x → Nd 2 Fe 14 B, and (3) amorphous → Nd 2 Fe 14 B, respectively [43].…”

Surface Morphology Investigations of Nanocrystalline R2Fe14B (R = Y, Nd, Gd, Er) by Atomic Force Microscopy

“…Different kinetics during quenching, i.e., different temperature gradients, leads to differences in cooling rate and crystallization speed. It is known [27] that crystallization of Nd2Fe14B-type material during rapid quenching proceeds in two stages: at first, TbCu7-type metastable phase arises along with a small amount of α-Fe phase. Then decomposition of the TbCu7-type phase occurs with Nd2Fe14B-type and α-Fe phases formation.…”