High-temperature rotating cylinder rheometer for studying metallic glass forming liquids.

A high-temperature Couette rotating cylinder rheometer has been developed for shear viscosity investigations of metallic glass forming liquids under precisely controlled flow and environmental conditions. These materials generally exhibit viscosities in the range of 10-2 to 10-1 Pa s above their liquidus temperature. While knowledge of the viscosity is crucial for estimating the glass forming ability and processing capabilities of these liquids, accurate rheological measurements are challenging due to their vulnerability to oxidation and contamination from the crucible and processing environment. Thus, the present device was constructed to measure the shear viscosities of these reactive melts in an inert atmosphere using shear cells manufactured from isostatically pressed graphite. A custom suite of LabVIEW programs provides all the necessary data acquisition tools and controls for the motor, inductive generator, sample temperature, and torque sensor. The setup includes a proportional-integral-derivative controller that allows for both isothermal and continuous heating/cooling experiments from room temperature up to 1400 K. The system is calibrated using NIST reference oils at room temperature. To demonstrate the functionality of the apparatus at high temperatures, the viscosity of the metallic glass forming alloy Zr59.3Cu28.8Al10.4Nb1.5 (AMZ4) was measured above the melting point and was found to be in excellent agreement with previously reported reference values from levitation-based measurement techniques.