Ultrasonic vibrations as an impulse for glass transition in microforming of bulk metallic glass

The paper presents the idea of the utilisation of ultrasonic vibrations in microforming at elevated temperature of a bulk metallic glasses as an impulse of additional energy for initiating a glass transition at lower than nominal temperature. The method of micro-upsetting at elevated temperature with non-uniform temperature distribution (MUNUT) was used. It is shown that applying ultrasonic vibrations on the tool could replace the part of the thermal energy needed for achieving the supercooled liquid state necessary for the microforming of bulk metallic glass. The results of research are limited to the analysis of two micro-specimens only and their final state of deformation. The commercial FEM code was used in the Thermal/Structural analysis class to determine the temperature distribution within the micro-specimen and to justify the linear approximation of this distribution. It was shown that the application of ultrasonic vibrations at 20 kHz frequency and the amplitude PP = 36.5 μm under the experiment conditions lowered the transformation temperature by approx. 32 °C. Results suggesting that applying ultrasonic vibrations could be also used as the tool which would provide additional energy for the transformation at the limited area of the micro-product.