Evidence of anti free volume creation during deformation induced nanocrystallization of Nd-Fe-B metallic glass

Abstract

The Extended X-ray Absorption Fine-Structure (EXAFS) technique was used to study the time evolution of the structure of Nd-Fe-B metallic glass undergoing nanocrystallization during mechanical milling. Negative as well as positive fluctuations in atomic density were observed, providing direct evidence of the creation of deformation-induced pairs of free volume and anti-free volume defects. These defects migrated during milling, leading to the atomic redistribution and precipitation of nanocrystals. Our results demonstrate that atomic defects caused by deformation of metallic glasses involve more extensive athermal changes in short-range order than nearest neighbour bond breaking as suggested by the free volume model. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) Deformation induces the formation of vacancy-interstitial pair type "free volume - anti free volume" defects in metallic glasses. Enhanced diffusion due to these defects leads to atomic redistribution and precipitation of nanocrystals in the amorphous matrix. In their Letter on page 169ff., the authors report on a study employing EXAFS to follow the time evolution of the structure of Nd-Fe-B metallic glass undergoing nanocrystallization during mechanical milling. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.