Thermoplastic embossing device to probe rheological changes of supercooled metallic liquids during rapid heating

The setup and working principle of a device designed for thermoplastic embossing and investigating rheological changes during fast-resistive heating of bulk metallic glasses (BMGs) is presented. The device was developed and custom-built at the Leibniz Institute for Solid State and Materials Research Dresden (Leibniz IFW Dresden) and is integrated into a universal testing machine. By varying the electrical-current pulse signal, the rate at which BMGs are resistively heated is controlled. Next to temperature and electrical resistance, the displacement of the punch, which penetrates the sample during rapid heating, is monitored. Additional pre-heating controlled by thermocouples allows for stable heating conditions to minimize heat extraction from the resistively heated specimen, which could eventually lead to damage of the device. The main focus of this device is to study fundamental phenomena under kinetic constraints evoked by fast heating conditions and to structure the surface of BMGs by thermoplastic embossing. A case study, which is carried out with Zr_52.5Cu_17.9Ni_14.6Al₁₀Ti₅ BMG, demonstrates the device's performance covering heating rate ranges of three magnitudes and the access to rheological changes during the devitrification and subsequent crystallization of the BMG during rapid heating. Furthermore, the present device was successfully used to nanostructure the surface of the BMG at elevated heating rates.