Granulation of Bulk Metallic Glass Forming Alloys as a Feedstock for Thermoplastic Forming and their Compaction into Bulk Samples

The various technologically important properties of metallic glasses are intimately connected to their amorphous structure that lacks the archetypical structural defects of polycrystalline metals and alloys, i.e. dislocations and grain boundaries. However, the amorphous structure also limits the application potential of this class of materials because of a macroscopically brittle behavior and size limitations. Consequently, with some exceptions, at least one dimension for technological products is limited to a few millimeters or even less. With the presented technological approach this drawback will be addressed. Our first results on several alloys show that with a dedicated instrumentation amorphous granulates can be successfully produced. By hot pressing in the supercooled liquid region, these granulates can be compacted into bulk shapes in the cm range. Further, due to the low viscosity of the supercooled liquid state, this technology disposes of a high formability. It is demonstrated that not only compact samples but also complex shapes in near net shape geometry can be produced. Results on the mechanical properties and microstructure will be discussed and related to important processing issues. Even though this technological approach does not directly address the second drawback of bulk metallic glasses, i.e. catastrophic failure due to highly localized shear bands, it is believed that this route offers possible pathways to improve this issue as well and, most important, to offer a technological route for implementing bulk metallic glasses into products of rather arbitrary shape and larger size.