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 Al₉₀Fe₅Gd₅and Al_86.8Ni_3.7Y_9.5were compared. In rolled Al₉₀Fe₅Gd₅, nanocrystallites were observed at shear bands, whereas none were observed in rolled Al_86.8Ni_3.7Y_9.5. 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 Al_86.8Ni_3.7Y_9.5, the shear bands contain a uniform distribution of defects with a density higher than the undeformed region. The preferential precipitation of nanocrystallites in rolled Al₉₀Fe₅Gd₅is attributed to a kinetic effect due to uniformly-distributed excess free volume in the shear bands.