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

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. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim