XRD investigation of binary alloy solidification.

The solidification of two binary alloys, In-10Sn and Sn-13Pb, has been investigated by X-ray diffractometry (XRD) at high temperatures. The high-temperature X-ray camera, which was mounted on a diffractometer, had a sample holder suitable for molten metals and operated in a controlled Ar atmosphere. Melts were cooled down slowly and XRD spectra were recorded step by step in order to monitor the structural evolution of the liquid prior to and during solidification. Temperature was kept constant while the XRD data were collected. The radial distribution functions (RDFs) were then determined from the spectra for each temperature. Experiments showed that atomic clusters form in the melt immediately before the appearance of the first solid. The experimental problems encountered in real-time monitoring of phase transformations involving liquid metals were looked at. To avoid convective motion in the liquid and to arrive at the best possible experimental conditions, we discussed the possibility of carrying out these studies at the reduced gravity found on the International Space Station.