Accessing thermoplastic processing windows in metallic glasses using rapid capacitive discharge

Abstract

The ability of the rapid-capacitive discharge approach to access optimal viscosity ranges in metallic glasses for thermoplastic processing is explored. Using high-speed thermal imaging, the heating uniformity and stability against crystallization of Zr 35 Ti 30 Cu 7.5 Be 27.5 metallic glass heated deeply into the supercooled region is investigated. The method enables homogeneous volumetric heating of bulk samples throughout the entire supercooled liquid region at high rates (∼105 K/s) sufficient to bypass crystallization throughout. The crystallization onsets at temperatures in the vicinity of the crystallization nose were identified and a Time-Temperature-Transformation diagram is constructed, revealing a critical heating rate for the metallic glass of ∼1000 K/s. Thermoplastic process windows in the optimal viscosity range of 10 0 -10 4 Pa·s are identified, being confined between the glass relaxation and the eutectic crystallization transition. Within this process window, near-net forging of a fine precision metallic glass part is demonstrated.