LAUSR

Abstract The melt of Ni31Si12 intermetallic compound was undercooled by a melt fluxing technique. The recalescence processes were in-situ observed by a high-speed camera and the solidification microstructures were analyzed by electron back-scattering diffraction. A sharp increase of the growth velocity was found at a critical undercooling ΔT*≈128 K and a second β2-Ni3Si intermetallic compound was observed around the primary Ni31Si12 intermetallic compound when the undercooling ΔT>119 K, indicating that the Ni31Si12 intermetallic compound is actually not stoichiometric. With the increase of undercooling, the microstructure changes from coarse striped grains, coarse dendrite to refined equiaxed grains, while the growth orientation transits from 11 2 ¯ 0 > , mixed 11 2 ¯ 0 > & 1 1 ¯ 00 > to 1 1 ¯ 00 > . Fragmentation of 11 2 ¯ 0 > -oriented dendrites with the reduction of interface energy and solute diffusion as its driving forces, is suggested to be the origin of grain refinement. Since fragmentation happens adequately upon the transition of growth orientation, no experimental evidences can be found for the formation of seaweed dendrite, which if occurs should not be an intermediate for grain refinement. The current work is not only helpful for understanding non-equilibrium solidification but also useful for controlling microstructures of intermetallic compounds.