Atomic-scale structural evolution in amorphous Nd9Fe85B6 subjected to severe plastic deformation at room temperature

Abstract

Understanding the deformation-induced nanocrystallization in amorphous alloys at room temperature is proved to be a great challenge. In the present study, the formation of vacancy-type defects richly surrounded with Fe atoms in amorphous Nd9Fe85B6 subjected to room-temperature high-pressure torsion deformation is directly evidenced by positron lifetime measurements combined with a coincident Doppler broadening measurement of the positron-electron annihilation photons. This demonstrates a direct experimental evidence for shear inducing the enrichment of Fe atoms in the deformed amorphous alloy. These results presented here are of importance for understanding the deformation-induced nanocrystallization and for the technique development of nanocrystalline materials.

Influence of HPT Deformation on the Structure and Properties of Amorphous Alloys

“…In [54], the structural evolution of amorphous Nd 9 Fe 85 B 6 subjected to HPT at room temperature was studied by measuring positron lifetimes. The study also included the determination of Doppler broadening of positron-electron annihilation photons.…”

“…The curve of the freshly prepared MS Nd 9 Fe 85 B 6 alloy (in the region p L ≥ 20 × 10 −3 m 0 c) lies between the curves of defect-free pure Nd and Fe and differs greatly from the curve of pure Bor. The analysis shows that the chemical environment surrounding the structural free volumes (V) in the freshly prepared alloy MS Nd9Fe85B6 is enriched in Nd and Fe atoms [54]. After HPT, the MS alloy curve moves to the line of defect-free pure Fe (horizontal line).…”

“…The introduction of shear bands using SPD has a significant effect on both the microstructure and atomic structure of metal glasses [41,[50][51][52][53][54][55]. According to some works, excess free volume is accumulated in shear bands in BMGs formed at ambient temperature [62,63].…”

“…The transformation path of the amorphous structure depends on the composition of the amorphous alloy and the SPD processing regimes. Among the interesting phenomena observed in amorphous alloys of some compositions is nanocrystallization during SPD processing at room temperature [41,[51][52][53][54]. In a series of earlier publications, it was shown that nanocrystallization in the amorphous phase occurs under deformation [66][67][68][69].…”

“…In a series of studies [41,42,49,[51][52][53][54]70], nanocrystallization during HPT of initially amorphous melt-spun (MS) Nd 12 Fe 82 B 6 , Nd 9 Fe 84 B 7 ribbons was investigated. In [52], the amorphous MS Nd 12 Fe 82 B 6 alloy ribbons were subjected to SPD by HPT at room temperature under a pressure of P = 5 GPa.…”