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_7.5Be_(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 (~10^5 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.

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