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

Abstract

A unique gradient furnace for directional solidification experiments with bulk Al-alloy samples developed at German Aerospace Center is presented. It allows 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 (CT) 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 seconds and 70m, respectively, with a field of view of 10x50mm2. Constant solidification velocities of up to 0.15mm.s-1 at a temperature gradient of up to 8K.mm-1 can be achieved in a temperature range of 537K to 1373K. A flat solid-liquid interface inside a rod-like sample with 5mm diameter is achieved by surrounding the sample by a thermal isolating graphite foam. Performance tests with hypoeutectic Al-10wt.%Cu alloy samples show the functionality of the furnace facility.