Extended Plasticity in the Supercooled Liquid Region of Bulk Metallic Glasses

Abstract

Bulk metallic glasses have good mechanical formability in viscous states. The 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 mechanism, and particularly whether such alloys deform by Newtonian viscous flow (m=1, where m is the strain rate sensitivity exponent) or not, remains a controversial issue. In this paper, existing data are analyzed and the apparent controversy is discussed. Results obtained from an amorphous alloy (composition: Zr–10Al–5Ti–17.9Cu–14.6Ni in at%) are presented. Dynamic structural evolution is characterized using electron microscopy and focus X-ray. It is demonstrated that, despite the fact that the deformation was carried out in the supercooled liquid range, concurrent crystallization of the amorphous structure occurred. As a result, a non-Newtonian behavior was observed.