X-radiography front tracking gradient furnace for directional solidification of bulk Al-alloys.

A unique gradient furnace for directional solidification experiments with bulk Al-alloy samples developed at German Aerospace Center is presented. It allows for in situ process control in solidifying samples by using x-radiography, and further insight into the solidification process is gained in combination with x-ray computational tomography on the solidified samples. Tracking of interfaces during directional solidification of bulk samples via in situ x-radiography (TIREX) enables the investigation of the melting process and observation of the movement of the entire mushy zone through the sample, tracing the solid-liquid interface during directional solidification and correlating the observations with the microstructure of the samples. Monitoring the temperature profile inside the sample by in situ observation of the length of the mushy zone is particularly important because the temperature gradient G and the rate of interfacial growth v determine the microstructure of solidification. The x-radiography setup offers temporal and spatial resolutions of 0.5 s and 70 µm, respectively, with a field of view of 10 × 50 mm2. Constant solidification velocities of up to 0.15 mm s-1 at a temperature gradient of up to 8 K mm-1 can be achieved in a temperature range of 537-1373 K. A flat solid-liquid interface inside a rod-like sample with 5 mm diameter is achieved by surrounding the sample by thermal isolating graphite foam. Performance tests with hypoeutectic Al-10 wt. % Cu alloy samples show the functionality of the furnace facility.