High-pressure-torsion deformation of melt-spun Nd9Fe85B6 alloy
Abstract
The effect of severe plastic deformation by high-pressure torsion (HPT) at room temperature and subsequent annealing on the magnetic properties and structural transformations of the melt-spun alloy (MSA) Nd9Fe85B6 is studied. The melt-spun ribbons in three structural states, such as nanocrystalline, mixed amorphous-nanocrystalline, and quasi-amorphous, have been subjected to deformation. In the nanocrystalline alloy, HPT leads to the decomposition of part of the Nd2Fe14B phase into the amorphous phase and α-Fe nanocrystals. The deformation of the alloy in the quasi-amorphous state leads also to the precipitation of a great amount of α-Fe nanocrystals; in this case, the amorphous matrix is depleted of iron. During the HPT of the MSA in the mixed amorphous + nanocrystaline state, both structural transformations occur. The annealing of deformed samples at above 500°C restores the two-phase (Nd2Fe14B + α-Fe) nanocrystalline state. This is accompanied by increasing magnetic hysteretic properties. The HPT has been found to suppress the formation of nonequilibrium magnetically soft phases, such as NdFe7 and Nd2Fe23B3, that precipitate upon annealing of the melt-spun amorphous alloy. This promotes the formation of an optimum nanocrystalline structure of the α-Fe/Nd2Fe14B composite material and an increase in its magnetic hysteretic properties because of enhancement of the intergranular exchange interaction. Compact micromagnets 6 15 mm in diameter and 0.2 mm thick, which were prepared from the Nd9Fe85B6 alloy using HPT and subsequent annealing, exhibit the following characteristics: B r = 11.4 kG, H c = 5.4 kOe, and ( BH)max = 17.1 MG Oe.
- Publication:
-
Physics of Metals and Metallography
- Pub Date:
- September 2007
- DOI:
- 10.1134/S0031918X07090050
- Bibcode:
- 2007PMM...104..238P
- Keywords:
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- 75.50.Ww;
- 81.40.Rs