Experimental study on rapid solidification process using a novel ultrasound technique

Solidification rate is a crucial parameter affecting the microstructure formation in rapid contact solidification processes. A novel ultrasound technique has been developed for measuring the phase-change interface movement during a rapid contact solidification process. This new method utilized the echoes from two reflection interfaces for tracking the solidification front. It is therefore possible to eliminate the temperature effect on the sound speed in metals. The rapid solidification experiments were conducted by impacting an aluminum substrate onto a shallow liquid alloy 158. Echo signals were detected successfully and the phase change front position was determined with high resolution. A theoretical resolution of 4.5 μm can be achieved under current conditions. Experiments were conducted to study the effects of initial metal temperature, liquid pool thickness and impact height on a rapid contact solidification process. The experimental results show that with an increasing impact height, the solidification rate increases which means the thermal contact resistance is decreased. Therefore, the newly developed method can provide useful data for correlating the thermal contact resistance in rapid contact solidification processes.