New initiating mechanism of coupled growth in directionally solidified Fe–Ni peritectic system in diffusive regime

Abstract A new initiating phenomenon of peritectic coupled growth was observed in directionally solidified Fe–Ni alloys under diffusion-limited growth condition. Although it is generally accepted that peritectic coupled growth is initiated by island banding, the present experimental results show that two phases coupled growth could also be initiated by planar primary phase in samples of different compositions. Two models were proposed to explain the new initiating mechanism of peritectic coupled growth. It was found that due to the solute pile-up at the planar primary phase interface, the liquid at the planar primary phase interface will be suitable for nucleation of the peritectic phase or constitutionally undercooled with respect to the growing primary phase. The simultaneous growth of the nucleated peritectic phase with the primary phase or the cellular primary phases with the intercellular peritectic phase can induce the formation of coupled growth.