Steady-state tensile viscous flow forming of bulk metallic glass

Tensile viscous flow is explored as a forming method for metallic glasses in their supercooled liquid temperature region. Bulk amorphous preforms with nominal alloy composition Zr55Cu30Al10Ni5 were produced by arc melting and tilt- and suction casting into a copper mould. A simple loading rig, in which the preform is suspended from a wire, combined with selective heating of the section to be deformed, avoids the need for complicated loading grips. Different strategies are evaluated to attach the sample to the rig and to selectively heat the central part of the specimen.Finite element models were compared with experiments to verify the design of the induction heating coil and optimize process parameters. Differential scanning calorimetry and X-ray diffraction measurements show that the material is glassy before and after deformation. The rapid decrease of flow stress with increasing temperature means that the process can be controlled thermally at constant load instead of mechanically at constant temperature. An asymmetric configuration, where the selective heating zone is moved relative to the specimen during the deformation, allows to form rods into wire by a steady-state process. The effect of deformation on induction heating under constant tension was found to be inherently self-stabilizing, reducing the need for precise process control.

► A simple setup is demonstrated for tensile viscous flow forming of bulk metallic glass to large aspect ratio.
► The flow stress of the part of the material to be deformed is lowered thermally, by local induction heating.
► Applying the mechanical load to the less-softened ends, via attached wires, is straight forward.
► An asymmetric configuration allows to form rods into wire by a steady-state process.
► For this asymmetric configuration, preparing the preform and attaching the wires requires no machining.