Solidification behaviour of undercooled peritectic Fe81.68Co18.32 alloy

Rapid solidification of undercooled peritectic Fe81.68Co18.32 alloy was investigated using fluxing method. With the increase of initial melt undercooling (ΔT), different microstructures were observed. For low ΔT, a typical peritectic microstructure, if ΔT exceeded a critical value, 177 K, metastable phase was observed in the as-solidified microstructure. On this basis, different solidification modes for peritectic Fe81.68Co18.32 alloy were demonstrated. When ΔT < ΔTcrit, the melt solidified with peritectic mode, peritectic reaction and peritectic transformation occurred, followed by extension growth of γ at the peritectic layer. When ΔT > ΔTcrit, the melt solidified with competitive nucleation mode, competitive nucleation occurred between stable and metastable phase, and metastable phase nucleated primarily from the undercooled melt as a result.