In contrast to most crystalline metallic materials, bulk metallic glasses (BMG) do not require post-cast processing or heat treatment as ‘full’ properties are achieved in the as-cast state. This, together with the absence of a phase transition and the sluggish crystallization kinetics opens up an opportunity for a wide range of processing methods. Fundamentally, they can be separated into two categories: direct cast BMG’s where critical cooling rates for a wide range of BMGs are lower than 100 K/s. This however can still be challenging for the direct casting process since during casting cooling and filling of the mold has to occur simultaneously even when processing parameters are carefully balanced. The direct casting method is particularly challenged when attempting to produce many ‘hollow’ shapes where internal tooling is not feasible. A second category is where the BMG is thermoplastically formed in the supercooled liquid region where it exists as a highly viscous metastable liquid. In this case the required fast cooling and forming are decoupled. In this presentation we will show that some recently developed BMGs can be strained up to 10,000% strain under forming pressures of as low as 1 atm. (105 Pa) before crystallization sets in. In order to effectively utilize this large formability we often cast the BMG in the form of a shaped preform or a parison. Examples of net-shaping of complex geometries with features on multiple length scales ranging from 200 nm up to 10 cm will be illustrated. The similarities between this process, superplastic forming and processing thermoplastics and the ease with which BMG’s can be manufactured in this way will be exemplified.
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