Effect of combined metal-carbon additions on the microstructure and structure of Sm₂Fe₁₇

Abstract

The effect of combined alloying additions on the structure and scale of rapidly solidified Sm-Fe alloys was investigated. Transition metal additions tend to promote the formation of the disordered TbCu 7 -type structure in Sm 2 Fe 17 alloys, as determined by monitoring the long-range order parameter. Essentially no order was observed for M ‫ס‬ Ti, Zr, V, or Nb. Thus, the structure was close to the prototypical TbCu 7 -type structure. With M ‫ס‬ Si, a large amount of order was observed (S ‫ס‬ 0.62), resulting in a structure closer to the well-ordered Th 2 Zn 17 -type. The microstructural scale was also affected by alloying. In this case, refinement depended on the substituent and also on carbon for microstructural refinement. The scale of the as-solidified grain structures ranged from 100 nm for SiC-modified alloys to 13 nm for NbC-modified alloys. The degree of refinement was directly related to the atomic size of the M addition. The refinement was the result of solute partitioning to grain boundaries, resulting in a solute drag effect that lowered the growth rates.

Phase formation and magnetic properties of SmCo5+x alloys with the TbCu7-type structure

“…The combined effect of the rapid solidification and alloying with Nb suppressed the formation of the Sm 2 Co 17 equilibrium structure, which requires the ordering of transition metal dumbbells. Previously, we observed that early transition metal additions inhibited the development of dumbbell ordering in Sm 2 Fe 17 alloys, leading to the formation of TbCu 7 -type structures, and, combined with C, resulted in grain refinement [14,15]. A higher resolution scan taken at long counting times between 2y ¼ 36 and 40 confirmed the lack of long-range dumbbell ordering, as shown by the absence of the (0 2 4) superstructure peak predicted at 2yB38:5 (Fig.…”

Phase formation in rapidly solidified R2T17 intermetallics

“…Non-equilibrium processing such as rapid solidification was found to promote the formation of the TbCu 7 -type structure with disordered arrangement of dumbbell atoms in the lattice [2][3][4][5][6][7] and considerably refine the grain size [8,9]. Alloying additions of Ti and Zr were found to suppress the formation of the equilibrium 2-17 phases, leading to stabilization of the disordered TbCu 7 -type structure [3,10]; additions of Ti, V, Zr or Nb combined with C contributed to stabilization of the disordered phase and refined the grain size during melt spinning [11,12]. The formation of partially ordered Sm 2 Fe 17 with Th 2 Zn 17 -type structure was found to be independent of the wheel speed, but the alloyed compounds displayed stronger tendency to form the TbCu 7 -type structure [11].…”