Extended plasticity in the supercooled liquid region of bulk metallic glasses

Bulk metallic glasses have good mechanical formability in viscous states. T he good formability offers a great advantage of fabricating near-net-shape structural components. Whereas large tensile ductility has been observed in metallic glasses in the supercooled liquid region, the exact deformation m echanism, and particularly whether such alloys deform by Newtonian viscous flow (m = 1, where m is the strain rate sensitivity exponent) or not, remai ns a controversial issue. In this paper, existing data are analyzed and the apparent controversy is discussed. Results obtained from an amorphous allo y (composition: Zr-10Al-5Ti-17.9Cu-14.6Ni in at%) are presented. Dynamic st ructural evolution is characterized using electron microscopy and focus X-r ay. It is demonstrated that, despite the fact that the deformation was carr ied out in the supercooled liquid range, concurrent crystallization of the amorphous structure occurred. As a result, a non-Newtonian behavior was obs erved.