Deformation-induced nanocrystallization: A comparison of two amorphous Al-based alloys

Using conventional and high-resolution transmission electron microscopy (HRTEM), the effects of rolling at room temperature on the microstructures of amorphous Al90Fe5Gd5 and Al86.8Ni3.7Y9.5 were compared. In rolled Al90Fe5Gd5, nanocrystallites were observed at shear bands, whereas none were observed in rolled Al86.8Ni3.7Y9.5. When HRTEM was combined with with Fourier transform filtering, nanoscale, low-density defects were imaged. In Al90Fe5Gd5, the shear bands contain few defects, which are concentrated at the boundary zone between the shear bands and undeformed region, whereas in Al86.8Ni3.7Y9.5, the shear bands contain a uniform distribution of defects with a density higher than the undeformed region. The preferential precipitation of nanocrystallites in rolled Al90Fe5Gd5 is attributed to a kinetic effect due to uniformly-distributed excess free volume in the shear bands.