DEFORMATION-INDUCED NANOCRYSTAL FORMATION IN SHEAR BANDS OF AMORPHOUS-ALLOYS

AMORPHOUS alloys formed by rapid solidification of a metallic melt are of considerable technological interest as high-strength materials1-8. As they are not in thermodynamic equilibrium, these materials tend to crystallize on heating9,10. A high degree of crystallization leads to embrittlement, but if it can be arrested when the crystallites are of only nanometre dimensions, the resulting amorphous-nanocrystalline co mposite actually has greater strength than the original amorphous mate rial11. There is consequently much interest in understanding the mecha nisms of crystallization. Previous studies have suggested that mechani cal deformation can induce crystallization12-16. Here we report the di rect observation of crystallization within the shear bands of aluminiu m-based amorphous alloys induced by bending. The crystals are face-cen tred cubic aluminium, 7-10 nm in diameter, and seem to form as a conse quence of local atomic rearrangements in regions of high plastic strai n. We suggest that mechanical deformation might therefore be used to f orm high-strength amorphous-nanocrystalline composites.