The effect of compression and tension on shear-band structure and nanocrystallization in amorphous Al90Fe5Gd5 :: a high-resolution transmission electron microscopy study

Using both conventional and high-resolution transmission electron microscopy (HRTEM), the effect of bending at room temperature on the microstructure of amorphous Al90Fe5Gd5 was investigated. In the compressive region, nanocrystallites formed at shear bands, along small cracks and at the fracture surface; in the tensile region, nanocrystallites were observed only at the fracture surface. Combining HRTEM with frequency filtering, low-density, nanoscale defects at shear bands were imaged. In the compressive region, both the shear bands and the undeformed matrix contain few defects. In the tensile region, there is a uniform distribution of defects within the shear bands. The preferential precipitation of nanocrystallites in the compressive region is attributed to a kinetic effect due to the uniformly distributed free volume in the shear bands. In contrast, the formation of the nanocrystallites at the fracture surfaces is likely due to adiabatic heating induced by fracture. (C) 2003 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.