Abstract:Upon deforming a metallic glass at low temperatures, shear tends to localize and this leads to a brittle behavior. However, in the high temperature, and particularly in the supercooled liquid region, homogeneous deformation begins to take place. A bulk amorphous Zr-10Al-5Ti-17.9Cu-14.6Ni alloy was observed to exhibit the Newtonian behavior at low strain rates but becomes n on-Newtonian at high strain rates in the supercooled liquid region. Structures of the amorphous material, both before and after deformation, were examined using X-ray diffraction and high-resolution electron microscopy. Results showed the presence of nanocrystallites in the deformed samples. Thus, the non-Newtonian behavior is attributable to the concurrent crystallization of the amorphous structure during deformation. A mechanistic model is presented to interpret the observed non-Newtonian result. A phenomenological approach is also used to develop the deformation map for bulk metallic glasses in the supercooled liquid region.

Key words: metallic glass; viscous flow; superplasticity; dynamic crystallization; amorphous alloys; Newtonian flow