Solidification and melting of high temperature materials: in situ observations by synchrotron radiation

Until recently understanding the solidification behavior of high temperature materials, including many intermetallic systems, required evaluation of a great number of individual solidification experimental results. An additional challenge was the reactivity of metallic melts at elevated temperatures. Alternative methods for in situ observation of solidification processes using the high-energy synchrotron X-ray diffraction, which came up in the last decade, are reviewed in the present work. Here, solidifying phases and transformation sequences are directly related to their X-ray diffraction pattern, which avoids any confusion caused by subsequent phase transformations especially in complex systems. By containerless processing with aerodynamic, electrostatic and electromagnetic levitation methods, adapted to the application at the synchrotron beamline, contamination of the melt with impurities is avoided, which can corrupt the results of solidification studies by conventional methods. To date, the majority of the studies is focused on metastable phase formation and the structure of undercooled melts. Current efforts on liquid–solid phase transformations under conditions close to the equilibrium, which provide a great potential for acquisition of phase diagram data of refractory and reactive alloys, are also addressed.