Dependence of the amount of a nanocrystalline phase in the amorphous Fe80B20 alloy on the degree of severe plastic deformation

Abstract

Conditions for the formation of nanocrystals in the amorphous Fe80B20 alloy under the effect of severe plastic deformation (SPD) have been investigated by electron microscopy and X-ray diffraction. The dependence of the size of nanocrystals and the fraction of a nanocrystalline phase that is formed during the crystallization of an amorphous alloy on the degree of SPD has been studied. It has been shown that the SPD induces nanocrystallization of amorphous samples. An average size of nanocrystals is about 6 nm. The formation of nanocrystals is observed only in the zones of localization of plastic deformation, i.e., shear zones. These zones have an elongated shape; their width is several microns; in these zones, regions of a low density of the material and, in some cases, even voids, are observed. The size of such discontinuities is from 5 to 50 nm. It has been found that an increase in a degree of deformation increases the fraction of the nanocrystalline phase. The estimations of the fraction of the phases performed by the method of resolution of the maxima present in the X-ray diffraction patterns into components showed that in the samples subjected to deformation by 15 rev of the anvils the fraction of nanocrystals is nine times greater than that in the samples subjected to deformation by 8 rev. At the same time, the average size of nanocrystals remains unchanged. Such behavior testifies to a step-by-step development of the deformation and its delocalization in the sample.