Steady non-Newtonian flow of Vitreloy-1 in continuous extrusion

The steady thermal flow evolution of Vitreloy-1 (Zr41.25Ti13.75Cu12.5Ni10Be22.5) during cominuous extrusion is simulated by means of finite element modeling. The conjugate coupling between fluid dynamics and heat transfer via convection, viscous dissipation, and temperature-dependent properties is implicitly accounted for in the finite element solver. The flow model incorporates the viscosity dependence on temperature and strain-rate, hence it accounts for flow deceleration near the walls as a consequence of cooling, as well as for non-Newtonian effects such as shear thinning. At the melt-mold interface, shear-rate dependent slip and imperfect thermal contact were accommodated. In order to assess the extent to which crystallization occurs during the flow a Lagrangian transformation of coordinates is implemented to track the temporal response of flow elements from a moving frame of reference. For a 5 turn channel within a 100 rum thick copper mold, where the melt is injected above its melting point (similar to 1000 K) at 1 mm/s and the mold walls are actively cooled at 373 K, the simulation predicts that the melt is quenched to near glass transition (similar to600 K) at a rate fast enough such that crystallization is entirely evaded, as the nose of the TTT curve (similar to900 K) is bypassed by virtually all flow elements, and consequently 5 mm purely arnorphous plate is extruded. (C) 2003 Elsevier B.V. All rights reserved.