Sluggish dendrite growth in undercooled Fe-Co-Ni-Si multi-principal element intermetallics

The (CoFe)₅₀Si₅₀ and (CoFeNi)₅₀Si₅₀ multi-principal element intermetallics (MPEIs) with a B2 ordering structure were synthesized by arc melting, undercooled using the glass fluxing technique and observed in-situ by a high-speed high-resolution camera. A sharp increase of the dendrite growth velocity was found for (CoFe)₅₀Si₅₀ and (CoFeNi)₅₀Si₅₀ at the undercooling of ΔT = 250 K and ΔT = 225 K, respectively, related to the disorder trapping that occurs at high undercooling. As a result, low-ordered regions were found by HR-TEM in highly undercooled (CoFe)₅₀Si₅₀ and (CoFeNi)₅₀Si₅₀ alloys. Compared with the previous reported binary CoSi, the maximum dendrite growth velocity is decreased by nearly one order for the (CoFeNi)₅₀Si₅₀ MPEIs. Such sluggish growth phenomenon does exist in present MPEIs for both cases of the absolute and the homologous temperature scale. It is suggested that the number of components might dominate sluggish dendrite growth of the B2 crystal and the effect of specific elements cannot be omitted. This study reported the dendrite growth behavior of MPEIs, which is helpful for understanding the non-equilibrium solidification phenomena, thereby providing a reference for controlling the non-equilibrium solidification process.