Grain refinement in solidification of undercooled Fe₂B intermetallic compound alloy

Spontaneous grain refinement widely occurs in solidification of highly undercooled solid solution alloys, but the case in stoichiometric intermetallic compound alloys is seldom concerned. In this paper, Fe2B alloy was undercooled up to 336 K to investigate the solidification structure's evolution with undercooling. It is shown that the equilibrium peritectic reaction L + FeB -> Fe2B is completely suppressed and there is only an Fe2B phase to solidify at various undercoolings. As the undercooling increases, Fe2B crystals change from a faceted into non-faceted morphology, and grain refinement takes place from 48 K undercooling until a fully refined solidification structure is obtained above 92 K undercooling. When the sample solidified at a large undercooling is immediately annealed at high temperature, the grains are coarsened quickly. In combination with the electron backscattered diffraction and transmission electron microscopy analysis results, it is suggested that the solidification stress-induced recrystallization triggers the grain refinement in Fe2B alloy.