Seebeck effect as an in-situ detection technique
in solidification of metallic alloys
During the solidification of a metallic alloy, the interface between the solid and the liquid can be looked upon as a thermocouple junction, provided that the two phases show a difference of thermoelectric power. Several experimental devices (Mephisto, Ramses, Efaistos) have been realised to measure the voltage generated by the interface. Experiments have been performed both on earth and under microgravity conditions (i.e. with and without convection), with different solidification regimes such as planar, cellular, dendritic or eutectic front.
When the interface is planar, the measured signal is directly proportional to the temperature interface. However, when the interface is no longer isothermal (e.g. dendritic) or when the alloy is multiphase (e.g. eutectic), a local current density appears due to the coupling between thermoelectric effects and temperature gradient. This voltage drop must also be taken into account, and more information about the interface morphology can be obtained.
We propose to give here a review about the information (undercooling, segregation, microstructure transition...) that can be expected from this kind of measurements in most solidification conditions. Practical aspects and technical problems will also be discussed.