Effect of high pressure torsion at different temperatures on the local atomic structure of amorphous Fe-Ni-B alloys

Abstract

The effect of the deformation temperature (293 and 77K) by high-pressure torsion (HPT) on the atomic structure of melt-quenched amorphous Fe83−xNiхB17 alloys (х=25, 29, 33) and their crystallization thermal effect upon continuous heating have been analyzed by method of Extended X-Ray Absorption Fine Structure (EXAFS) in synchrotron radiation, transmission electron microscopy, and X-ray diffraction analysis. HPT at 293K decreases the crystallization thermal effect, whereas HPT at 77K increases it regardless of the alloy composition. The observed effect is caused by the reversibility of the structural transformations in the alloys upon variation in the deformation temperature. According to the results of the structure examination, HPT at 293K leads to the formation of more ordered state (partially crystallized) of the initial amorphous alloys. On the contrary, HPT at 77K stimulates the formation of more disordered amorphous structure (by destruction of short-range order and an increase in the average values of the coordination numbers around the iron atoms in the first coordination sphere).