Rapid solidification of a FeSi intermetallic compound in undercooled melts: dendrite growth and microstructure transitions

Rapid solidification of a FeSi stoichiometric intermetallic compound was studied using the glass fluxing method. The recalescence process was in situ observed for the first time by the infrared high-speed high-resolution cameras. The dendrite envelope was found to be non-isothermal during the recalescence process. The growth velocity increased first, then decreased and finally held nearly constant. The average dendrite growth velocity for the recalescence process increased monotonically with undercooling and was described well by the dendrite growth model for a stoichiometric intermetallic compound. At low undercooling, the microstructure transition from coarse dendrites to refined grains was consistent with the dendrite fragmentation model and the chemical superheating model. At high undercooling, dendrite deformation triggers stress accumulation upon rapid solidification, thus providing the driving force for recrystallization. However, there were no evidences for annealing twins accompanied by recrystallization as well as random textures due to recrystallization nucleation. From the local misorientation map, the grain refinement mechanism was suggested to be stress-induced dendrite fragmentation. This study is helpful for not only understanding the intrinsic mechanisms of microstructure transitions in theory but also controlling microstructures and performance of intermetallic compounds in practical applications.